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Why Is Florida So Humid?

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AVERAGE ANNUAL PRECIPITATION FOR FLORIDA

LEFT CLICK ON IMAGE TO ENLARGE

“Why is it so humid in Florida?”

There is no single, simple answer.  Here are eight reasons, most of which are interrelated.  After this listing, amplified explanations are available:

1.  Most of Florida is a peninsula which, by definition is bordered by water on three sides.  The adjacent sea water is the most important source of moisture for the atmosphere.  That part of Florida which is not a peninsula, the panhandle, is also bordered by sea water on the southern boundary.

2.  Sea breeze convergence carries moisture over the land.  Air that has converged near the surface will rise and under the right conditions will form clouds that provide precipitation.  The precipitation is simply distilled sea water.  In some parts of Florida sea breeze convergence provides almost two-thirds of the annual precipitation.

3.  Florida is located along the eastern margin of the continent where warm waters arrive from the North Atlantic Gyre.  Warm waters mean higher evaporation rates and the warmed air is also able to support more water in the vapor state than if it were cooler.

4.  The relatively low latitude location of Florida provides for warmer temperatures which in turn give the air more thermal energy necessary to support large amounts of water in the vapor state.  The warmer temperatures also provide for significant convectional uplift of air which is a key factor in the development of many of Florida’s rain clouds.

5.   Florida’ vegetation transpires large amounts of water vapor (into the air).

6.   Numerous fresh water surfaces within the state provide moisture to the air from evaporation.

7.   Weather systems moving from east to west with the “Trades” provides moisture to the state – especially during the Atlantic hurricane season.

8.   Winds associated with fronts, especially pre-cold frontal winds bring vast amounts of moisture to Florida from components of the south.

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MORE DETAIL

1) Most of Florida is a peninsula and by definition it is surrounded by water on three sides.  The rest of the state (the Panhandle) is also coastal.  The surrounding water is the source of a great amount of moisture for processing through the hydrologic cycle.  But, being peninsular is not reason enough for Florida to be humid.  As case in point is the Baja Peninsula of Mexico.  Look at this comparison of the two peninsulas:

In some instances left clicking twice will be necessary to enlarge.

2) The geography and physiography is such that sea breezes of the Atlantic side of the peninsula converge with sea breezes of the Gulf side of the peninsula.  The zone or line of convergence is seldom at the “center” because the sea breezes are seldom of the same strength.  As a general rule Atlantic side sea breezes of the peninsula are stronger than Gulf side sea breezes of the peninsula.  In any case, these sea breezes carry moisture in the vapor form the origin of which is evaporation off the sea surface.  When sea water evaporates the dissolved solids stay behind; therefore the cloud droplets formed when the sea breezes converge and then rise are made of fresh water.  In simplistic terms I have described one of Natures own distilleries of fresh water.  Air that has converged at or near the surface will rise and rising air cools adiabatically.  If that cooling air contains ample moisture the dew point temperature will be reached relatively quickly and further cooling cause by continued ascension of the air causes condensation which releases heat.  That added heat usually causes the air to become buoyant enough to continue rising to form clouds that provide precipitation.  This is akin to a hot air balloon rising through air that is cooler than the air inside the balloon.  Cumulonimbus commonly form when this happens.

LEFT CLICK PLEASE, TO ENLARGE IMAGE

In South Florida there are years that two-thirds of the annual precipitation is provided during the warmer 6 months and most of that precipitation is due to sea breeze convergence.  This is a real paradox to me because the huge amount of precipitation from sea breeze convergence (sometimes 40” or more) is the result of weather circulation systems that do not show up in the isobaric configurations of a national weather map!

Of course, statistics vary from year to year depending partly upon the amount of tropical activity due to tropical disturbances (waves), tropical depressions, tropical storms, and hurricanes.  The whole sea breeze convergence process happens most often when the synoptic pressure gradient is weak (synoptic systems are those lows and highs that are seen on the national surface analyses).  Except when tropical synoptic systems are dictating the pressure gradient (e.g. hurricanes) the warmer 6 months of the year are when sea breeze convergence is most likely to occur.  In the cooler 6 months synoptic systems that migrate generally from west to east across the United States dominated the flow patterns at the surface.

3) Florida is located along the eastern margin of the continent.  As in all continents except Antarctica, the eastern margins are generally more humid than the western margins.  The principle reason for this is that the water at the eastern margins is generally warmer than the water at the western margins.  The warm boundary currents belonging to the gyres of the respective oceans are on the western margins of the oceans (which is the same as saying the eastern margins of the continents).  Part of the North Atlantic gyre circulation (sometimes called the Gulf stream gyre) enters the Caribbean and eventually much of it travels through the Yucatan Strait (the gap between western Cuba and the Yucatan peninsula) to flow into the Gulf of Mexico as the Loop Current.  This, then, circulates warmer water and enhances the moisture potential for the air on the Gulf side of Florida.  The Florida Current segment of the gyre provides considerable thermal energy along the east coast of Florida.

LEFT CLICK TO ENLARGE IMAGE

The warmer the water the higher the evaporation rates and therefore the more moisture gets into the air in the vapor phase.  NOTE:  Remember, water vapor is invisible so I’m not talking about clouds – but – clouds develop as a result of either the condensation of water vapor (liquid droplets) or the deposition of water vapor (ice crystals).

IDEALIZED CIRCULATION ON A HOMOGENEOUS GLOBE

4) Most of Florida is in the low latitudes defined as that part of the world between the Equator and 30˚ latitude.  Downtown Jacksonville which is at the north end of the state’s Atlantic side is at 30.32 degrees north latitute.  I have shown the location of the 30^th parallel on the map of”idealized air circulation on a homogeneous globe” (above) and on the map of the boundary currents before that.

You might know that the planetary circulation is not as simple as shown above because the earth’s surface is far from being homogeneous (the same all over).  The most obvious surface difference is that between land masses and oceans.  Furthermore, there is a hemispherical difference in that category – 39% of the northern hemisphere is land but only 19% of the southern hemisphere is land.  Because of earth surface heterogeneity (differences) the planetary circulation is not nearly as ordered as shown above nor do the hemispheres mirror each other as perfectly as shown.  And – very obvious seasonal differences exist between the continents and the adjacent oceans.  (NOTE:  All of that is “fuel” for another tutorial topic which is likely to be addressed on this site at some time in the future).   There is one aspect of this that I want to mention up front at this time since some of you know about the “Bermuda High.”  It is a warm season phenomenon and in effect, the south half represents the northeast trades (over the Atlantic of our hemisphere) and the north half represents the prevailing westerlies (over the Atlantic of our hemisphere).

Since the lower latitudes have higher sun angles and therefore more intense solar radiation than the higher latitudes, lower latitude surfaces (of both the land and water) get warmer.  This added warmth not only causes higher evaporation rates over water and moist land but also more convection over the heated land than would exist were it colder.

Convectional uplift of air is a key factor in the development of rain clouds, providing there is an adequate supply of moist air.  And – think about this:  When air is heated by the surface and then rises due to it’s positive buoyancy it does not leave a vacuum behind.  Air must flow in to take it’s place and in Florida that is moist air which, in turn, is heated and rises.  Most clouds providing precipitation result from air rising one way or another.

5)  The warmth of Florida along with its vegetation allows for high transpiration rates.  Transpiration is the process whereby plant leaf surfaces cast water vapor into the air.  A mature oak tree in the Summer will put about 500 gallons of water daily into the air in this way; an acre of mature but still green-leafed corn about 2000 gallons a day; an acre of densely distributed invasive species of the melaleuca tree in the everglades is believed by some to transpire four times as much as a comparable area in native saw grass!

6)  Florida is a state with numerous surface fresh water features within it that provide high evaporation opportunities.

Lake Henderson on the east side of Inverness, Florida

Two left clicks will enlarge this photo nicely.  It is my favorite image of a beautiful lake where I love to sail my little sloop – taken by my photographer son, Colin Toney.

A traveler in the state finds remarkable beauty in glades, lakes, marshes, and rivers.  You might find it interesting (and even sad) that before humans began controlling it, the famous everglades was a 40 mile wide river whose water crept generally southward issuing fresh water into Florida Bay.  I’ve been told that the rate of movement was so slow that strong winds from the south would temporarily but significantly reduce the discharge into the bay and even sometimes cause the water to flow backwards.  Currently, Florida Bay is far more saline than it used to be because so much less fresh water empties into it these days (due to human usage, and interference through water storage and flood control).

7)  Florida is downwind of the North Atlantic segment of the global-scale N.E. Trades.  The Trades, rather than a specific wind, represent a planetary-scale force that causes weather systems to move from the east toward the west across the low-latitude portions of the oceans.  Examples of these weather systems are the array of tropical lows ranging from tropical disturbances on the lower end of the intensity scale to hurricanes on the higher intensity end of the scale.  All of these types of lows bring moisture to Florida.

If you want to get a general idea as to why weather moves across most of the United States from west to east and why hurricanes (and the lesser tropical lows) move generally from east to west across the Atlantic just look at the guiding forces on the “homogeneous globe” diagram – the prevailing westerlies and the northeast trades.  As for the oft-asked question, “Why don’t the synoptic systems move in the same direction as the arrows showing the westerlies and the trades? – it’s the rightward Coriolis effect in the northern hemisphere that is mostly responsible.  Mid-latitude cyclones, air mass anticyclones, and tropical lows act as separate entities which rotate the way they do because of the Coriolis effect but move in translation over the land and the ocean in a direction influenced by the Coriolis Effect.  Here are a couple of links on the Coriolis effect:

http://cloudman23.wordpress.com/2008/10/02/the-coriolis-effect-in-the-real-world-a-tutorial-part-1/

There is a link within the one above to take you to Part 2 of the Coriolis effect subject if you wish.

8)  Air ahead of cold fronts moves almost parallel to those fronts.  It responds to the pressure gradient of the middle-latitude systems containing the fronts.  In Florida those pre-frontal winds are generally from some component of the south (typically southeast).  SPECIAL NOTE: Winds are named in accordance with the direction from which they are moving.  In other words, a southeast wind is a wind blowing from the southeast toward the northwest. What that means is that when cold fronts are moving through Florida the pre-frontal winds are carrying relatively warm and humid air from lower latitudes.

It is this warm and humid air that provides the moisture for condensation making the lines of clouds ahead of the fronts and along the fronts.  The moisture is not being brought down by the cold air but rather, the cold air is forcing the warmer air ahead of it to rise and cool adiabatically just as moisture bearing air does when it is lifted up the windward side of a mountain range.  In fact, I envision cold fronts as moving mountains along whose leading surfaces air is forced to rise, often to a level of free convection where it then “rises freely by convection” forming some very powerful lines of thunderstorms.  Additionally, the dynamics and temperatures aloft help to create squall lines out ahead of and nearly parallel to many of those cold fronts.

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FLORIDA WATER IS NOT AS

ABUNDANT AS IT SEEMS

It is apparent that there are several reasons for Florida’s sometimes notorious humidity.  It may seem that the explanation you have just read is more detailed than most but the truth is, I have not covered all aspects, particularly those dealing with the winds aloft.  Obviously, a variety of circumstances cause the large amount of moisture in the air over Florida as well as the amount of precipitation, the latter being enough for most of the state to fit within the parameters of the Humid Subtropical climate – though a small part of South Florida is classified as a Tropical Savanna climatic zone.  But – some people are shocked when they learn how little of the water raining upon Florida is available to them.

I will use “ball park” numbers I am comfortable with for the sake of simple illustration.  To keep it simple, I’ll round off numbers used to illustrate a typical annual water budget for South Florida.

Annual precipitation is about 60 inches.

20” evaporate

20” transpire

18” discharge into the sea by surface runoff and groundwater transport

2” remain for all other usage!

People move to Florida and clearly see “water, water everywhere.”  But the truth is that very little of that water, probably less than 3% is captured and exploited by humans.  It is always a good idea to conserve water in Florida, even during the rainy season.

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MORE ON HUMIDITY

The word “humid” is used in a variety of ways by the general population and humidity is expressed in more than one way by meteorologists.  “Relative humidity” is a percentage expression of the amount of water vapor in the air compared to the amount that could exist within it at that particular energy level (based upon its temperature).    The left column below shows air temperature in both Celsius and Fahrenheit and the right column shows how much vapor, in grams, a kilogram of that air can support in the vapor (gaseous) state at those temperatures.   Consider the following illustrations using the chart provided.

Left column is the Temperature in degrees Celsius and (Fahreheit)

Right column is grams of water vapor per kilogram of air representing specific humidity at saturation.  Saturation indicates 100% relative humidity.

-40 (-40)                                             0.1

-30 (-22)                                             0.3

-20 (-4)                                               0.75

-10 (14)                                              2

0 (32)                                                 3.5

5 (41)                                                  5

10 (50)                                               7

15 (59)                                               10

20 (68)                                              14

25 (77)                                              20

30 (86)                                              26.5

35 (95)                                               35

40 (104)                                             47

Here are four usages of the chart above

to give you a “feel” for humidity.

1.  If the specific humidity of 68 degree Fahrenheit air is 3.5 grams per kilogram, the relative humidity is 25%.  (3.5 is 25% of 14).

2.  If  there are 10 grams of water vapor in a kilogram of 77˚F. air near the surface that air has a relative humidity of 50%.  Why?  The chart tells us the air has the thermal energy to keep 20 grams of water in the vapor phase so if there are only 10 grams in the vapor state that represents one-half (50%).  On the other hand, if the temperature where then to drop down to 59˚F. the relative humidity would be 100%!  This is because 10 grams of water vapor in 59 degree air represents the saturation level for air at that temperature.  In this case, the meteorologist would say that the 77 degree air (at 50% relative humidity) had cooled down to its “dew point” (59 degrees) – the point or temperature where condensation would occur if there were any further cooling.  If that cooling occurred on the ground or on your windows overnight dew would form; if it occurred near the surface fog droplets would form; if it occurred further up, cloud droplets would form.  NOTE:  Actually, fog is no more than cloud close to the surface.

3.   If air over the Arctic at -10 degrees Fahrenheit had a relative humidity of 100% a kilogram would have 2 grams of water (per kilogram) in the vapor phase.  Yet if the relative humidity of 104˚F. air over Yuma, Arizona was a very low 15%, that air would contain more water in the vapor phase than the 100% relative humidity Arctic air.  Why?  Because 15% of 47 grams is 7.05.  More than 7 grams of water vapor in a kilogram of air is a lot more than 2 grams within a kilogram.  Therefore, even though the relative humidity of the Yuma air is a low 15% compared to 100% for the Arctic air, the hot Yuma air has more than 3 ½ times the amount of water vapor in it than the colder Arctic air.  So – the Yuma air at 15% relative humidity has more water vapor in it than the 100% relative humidity air of the Arctic location!  A meteorologist might say (if he/she is being careful), “The specific humidity of the Yuma air is much higher, more than 3 ½ times higher, than the air at the Arctic site.”  Yes – this is a paradox.  What I hope you learn from this is that the warmer the air, the more energy it has for keeping water in the vapor state and as the temperature increases the ability to hold water in the vapor state does not increase linearly, but exponentially.

You can see that on the chart.  For example, 20˚Celsius air has the ability to keep 14 grams of water per kilogram of air in the vapor state.  But double the temperature to 40˚Celsius and the water vapor “capacity” does not double; in fact, it more than triples!  The calculator in my computer tells me that it increases 3.3571428571428571428571428571429 times.  Please memorize that number.  There will be a test question on the midterm!  LOL

4.   If a kilogram of 77˚F. air was keeping 18 grams of water vapor within it, the relative humidity would be 90%.  Why?  Because 18/20ths (reduces to 9/10ths) translates to 90%.  You may find this hard to believe but many of my college students (particularly in the last 20 of my 41 year teaching career) in pre-testing could not successfully change a fraction into a percent.  Divide the numerator by the denominator and then multiply by 100 to get percent.  Percent means “parts per 100.”  So, 18 divided by 20 (or 9÷10) = 0.90.  0.90 X 100 = 90.  Most people instantly recognize that 0.90 is 90 one-hundredths and therefore do not need to multiply by 100.

An earlier posting on the subject of humidity can be found here:

http://cloudman23.wordpress.com/2008/08/25/why-does-it-feel-so-humid/

More related topics will appear in the near future, among them, a fundamental presentation on adiabatic processes that form clouds with a high potential as precipitation providers.  Adiabatic processes are so important to us that without them, almost all of the land of the world would be desert.  If you are interested, click on the following link to a November, 2008 post for a starter:

http://cloudman23.wordpress.com/2008/11/21/1364/

FLORIDA’S RAINY SEASON – 2009

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A related post, “Why Is Florida So Humid” has been added.

It can be found here:

http://cloudman23.wordpress.com/2009/07/04/why-is-florida-so-humid/

About a third of the way into May I noticed that television weather reports and a few of my acquaintances were starting to suggest that “perhaps” Florida’s rainy season had begun.   To be sure, before the middle of May many parts of Florida had been experiencing very significant rainfall events, some of those places on a daily basis.  One of those places was northeast Citrus County where I live.  However, I doubted that those rainfall events signaled the beginning of the “real” rainy season because my experience living much further south in Florida had conditioned me to considered the “true” rainy season to be that time when precipitation was due almost entirely to mesoscale systems, namely sea breezes and sea breeze convergence within the peninsula.  And – unless the views were severely obscured by buildings or dense stand of trees, at those times one can detect evidence of thunderstorms within hearing and/or seeing distance on almost a daily basis.

Florida’s rainfall this May was almost entirely due to weather systems of a much larger magnitude than the mesoscale – systems that show up on the national weather maps (middle-latitude cyclones with their associated frontal weather, et. al.).  Those systems, along with anticyclones (rotating highs) are often referred to as synoptic systems.

I’ve always found it interesting that the majority of our annual precipitation in peninsular Florida occurs (on the average) as a result of weather systems far smaller in magnitude than either the mid-latitude synoptic systems or the tropical synoptic systems such as hurricanes and tropical storms.

Here are three graphic illustrations of the synoptic nature of our May events followed three more images of today’s weather (June 2, 2009) over the Florida peninsula.  Comments labeled A through F  follow each illustration:

70 minute loop begins 5:28 pm EST, May 17, 2009

MOST ALL IMAGES IN THIS WEB-LOG ENLARGE

WITH A LEFT CLICK OR TWO

AND

IN MOST CASES IN ORDER TO ACTIVATE LOOPS

YOU MUST FIRST ENLARGE.

A.  In this 70 minute loop (starting at 5:28 PM EST on May 17^th notice the cold front that shows up well along a line from eastern Tennessee down to southern Mississippi.  If one were to see only the Florida peninsula portion of this image I can see how he/she might immediately assume that this was a sea breeze convergence day.  But as you can see, this is pre-cold frontal weather being drawn northward.  Not to say the warmer land surface and some convergence did not play a role, it is nonetheless clear that the weather is dominated by the synoptic scale.

B.  This 70 minute loop of the same system shows very nicely the pre-frontal nature of Florida’s rainfall by virtue of the fact that it has moved on in accordance with the general motion of the cyclone across the United States from west to east.  This loop starts at 11:28 PM EST on May 17^th.

C.  Here is an impressive array of alternating lows and highs of the synoptic scale on May 26.  At this time the movement of the lows was almost perfectly synchonized in the diurnal mode so that each day, with the help of the intense heating of the peninsula, we got significant rainfall in my neighborhood (latitude 29˚North by longitude 80.4 West – to the nearest 10^th of a degree).  Notice the lows centered off the Georgia coast, south-central Alabama, and Texas – all three with associated troughs.  Each of those provided my neighborhood a great deal of rain and certainly cramped my style as I was attempting to spend a lot of time outdoors landscaping and doing my annual manicuring of my woods.  But – because of three years of drought here, I was thanking the Great Guy In The Sky for each and every drop and respecting His audible commands to stay safely indoors in the form of lightning hits that were uncomfortably close.

I was surprised to learn recently that the National Weather Service Forecast Office has declared May 11 to be the beginning of the 2009 “rainy season” of Florida.  This is a full 9 days ahead of May 20, the mean starting date.  Who am I to disagree with the experts?  It matters not in the real world I suppose – only in the academic world in which people like me often get lost.  The bottom line is that we need the rain and no matter whether May’s events were “true, traditional” rainy season events or not, they were a blessing.

Now lets take a look at weather over the peninsula a little earlier today.

UNLIKE THE FIRST TWO IMAGES –

THIS IS A STILL – NOT A LOOP.

D.  Today, June 2, 2009, the radar shortly before 3 pm EST is showing precipitation as a result of sea breeze “fronts” along both sides of the peninsula.  I suspect convergence is occurring in the south part as shown by the beginning of development over some of the glades south of Lake Okeechobee.  This is more like a Florida “rainy season” day as I have learned to know it but even today – a synoptic system is providing a noticeable influence (see next two images). For those of you who live in my neighborhood, the Crystal River winds at the time of this observation were 7 mph from the west and that is ample to bring in moist air which is rising over the heated land to form the showers that are appearing on this radar image.

E. Later today the thunderstorms became more intense and in the still radar image above you can see a decided concentration toward the western side of the peninsula.

F.  And here is a synoptic map showing the low (with its associated fronts) that is influencing Florida’s weather today.  There is a “rule of thumb” in meteorology that the air ahead of a front moves more or less parallel to that front.  If you will simply extend in your mind’s eye the warm front further toward Florida you will realize that there is a force over most of Florida tending to make smaller weather systems (like mesoscale thunderstorm complexes) move toward the WNW.  Apparently the winds aloft are not strong enough to counteract that.

================================================================

Here are some interesting statistics for two locations in Florida providing some geographical contrasts along the peninsula.

Ocala averages almost 50” of rainfall per year of which nearly two-thirds falls in May through October.

Homestead (south of Miami) averages nearly 60” per year of which over three-fourths falls in May through October.

Here are the actual numbers (statistical means):

Ocala (in Central Florida) 49.68” annual     31.10” May through October = 62.6%

Homestead (south of Miami) 58.20” annual    45.70” May through October = 78.5%

For further information about Florida’s rainy season  here is a safe link in the pdf format from NOAA.

http://www.srh.noaa.gov/images/mfl/news/Rainy_Season_Beginning_2009.pdf

Yours Truly,

Tonie A. Toney

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The Hurricane Season of 2009 Has Begun!

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This image shows no tropical activity 15 minutes into our 2009 season (not surprisingly) but you can clearly see the clouds development with a stationary front cutting diagonally across the image.

The Atlantic/Gulf of Mexico/Caribbean hurricane season “officially” begins on June 1.  The fact that Tropical Depression 1 formed about 4 days before the official season’s beginning is not an indication of an active hurricane season this year.  There seems to be no relationship between early activity and the “busyness” of that season.  In fact, there is a real possibility that an El Niño event will be strong during what we consider the peak activity period of our season (the approximate middle of the 6 month long period).  Eastern Pacific sea surface temperatures have been rising steadily for the last several months pointing to the El Niño possibility.  That means is that our 2009 season might be less active than usual if the ENSO comes to fruition.  ENSO = El Niño Southern Oscillation.  BUT, even if a strong El Niño develops it is no time to let down one’s guard if living in “hurricane country.”  1992 was an El Niño year and that was when Andrew occurred.  My house in Homestead was a total loss.

I was extremely well prepared back then (August 24, 1992) but hurricane Andrew slammed in as a category 5.  However, we did have a plan and it worked to the degree that no one in my family was physically hurt.  Only one window had a small crack but – the roof failed and the damage was almost beyond belief for us.  Since Andrew was a relatively dry storm our windows holding firm did make it so that we were able to salvage some valuable items afterwards because the wind did not gut the house.

We stayed in the community and helped rebuild.  We had great insurance and our house was reconstructed in one year to a higher standard.  During that time we four lived in a 25’ travel trailer that I purchased for that purpose but kept for several years afterwards to use for recreational and educational travel.

If you live in “hurricane country” then you have choices.  Some of us have more choices than others but you should at least have a plan that is clearly articulated to and understood by each member of your household.  Shall you be well prepared or do you choose to become a potential victim who is dependent upon others almost immediately after a storm?

I urge you to follow to the best of your ability those preparation suggestions made by your local and federal agencies.  Some of us are more fortunate than others in what we are able to do to protect our dwellings – that is, those of us who are lucky enough to have a place we call home.

In my new post-retirement community and in neighboring communities (Citrus and neighboring counties)  I see what I consider to be real paradoxes or, at the very least, some irony.  I’m reminded (but to a somewhat lesser degree) of one of my Homestead neighbors who drove a Mercedes while his wife drove a BMW; they owned a very large boat moored at a dock in nearby Biscayne Bay, an ultra-light aircraft and a twin Cessna – yet they had no window protection of any sort for their home.  I speculate that it was not a matter of the cost of such protection but more a matter of priorities and life style with perhaps a little measure of denial thrown in.

Some people in my part of Florida feel that by being inland they have some sort of immunity to the ravages of hurricanes.  Yes – it is an advantage being inland, especially if on high ground but it does not offer any guarantees.  Most deaths in hurricanes (on the average) are due to high water and being away from the storm surge zones and areas prone to flooding from the storm’s downpours makes for a safer situation – generally speaking.  But, high winds can play havoc particularly when items become projectiles in the wind.  It is a fact that if the wind velocity doubles, the force it exerts upon a surface it is striking at right angles quadruples!  People in my part of Florida experienced a lot of activity if they were here in 2004 but the wind velocities were luckily relatively low.  Only modestly higher wind velocities would have produced exponentially greater force and far greater damage.  Furthermore, tornadoes and microbursts occur within hurricane bands and neither have a preference for locations near the coast.

Come early August we will have been in our new home for four years.  Our first major purchase when moving in was window and door storm protection.  We had tended to that “need” before we were even set up with a cable connection for our televisions and computers.  For the first two years that we were here I participated in a number of hurricane expos as the “hurricane resource person” on site.  There were expo participants who were in the business of selling, fabricating, and installing storm protection to homes and businesses.  Most visitors were there to learn about hurricane safety and hurricane protection.  But one particular type of visitor seemed to come to these expos in order to exercise their debate skills on the pros and cons of storm protection for windows and doors.  I was amazed at times by the level of denial and warped rationalization that I witnessed.  Some argued that they refused to concern themselves with such matters and would just let their insurance take care of it for them.  There was little if any consideration for how they would deal with losses of personal items, safety issues if they were not to evacuate, safety issues if they were to evacuate, where they would go if they did evacuate in time, and how they would handle matters when they returned if things were torn all to hell!  I am convinced that some of the men I talked to felt that it was a manly thing to face a storm raw without preparation – even though in some case it meant leaving their house mates far more vulnerable than necessary.  To my mind, they had it backwards  – a real man takes care of his own and is available to help others as well.

I can testify, by experience, that the trauma of a storm itself often does not compare to the trauma of the immediate aftermath and rebuilding.  Looting, for example and other forms of predatory behavior can occur.  In heavily damaged areas the majority of those who come to help are good people with good intentions but there is one whole class of “helpers” who are there to take victims for a ride they will never forget.  In South Dade County, where Andrew first struck the U.S.A. the divorce rate just about doubled for the next few years.  Stress and anxiety were on a very high level.

So – please think in terms of the big picture when a hurricane visits – not simply the weather event itself.  Think in terms of what you’ll do if you lose electricity for several days and how you will fare food-wise if you need to go for a week or more without provisions and how you’ll communicate.  Cell phones go out of commission when the transmission and relay towers are damaged.  Then there are the special needs people who absolutely must make arrangements for care in the event of a serious storm.

Please be prepared to the best of your ability.  If you later consider all of that planning and work to be for naught because no hurricane occurs in your region – there will be more seasons to follow for which you will again be ready and if, near the end of the season, you have a box full of “emergency food” there are surely some places near where you live to donate it to the needy.  After all, the end of the official hurricane season (November 30) and Thanksgiving (November 26) are pretty darned close to each other.

Here is this season’s list of names; tropical cyclonic systems will receive names in order from this list once they reach tropical storm intensity; tropical storm sustained winds fall in the range of 39 mph to 73 mph; of course they retain their names if they become hurricanes (74 mph or more):

Ana
Bill
Claudette
Danny
Erika
Fred
Grace
Henri
Ida
Joaquin
Kate
Larry
Mindy
Nicholas
Odette
Peter
Rose
Sam
Teresa
Victor
Wanda

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TORNADO WARNINGS TONIGHT – SOUTH GEORGIA, NORTH & CENTRAL FLORIDA

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Tornado and severe weather warnings were released about 30 minutes ago for South Georgia, North and some of Central Florida.  As the night progresses it is likely that more of Central Florida will be involved.  My county, Citrus, has already been alerted.  Please be sure that you take whatever precautions you are equipped to take in such circumstances.  If you have a weather alert radio please be sure it is positioned so that it will awaken you to critical bulletins.

This alert has been triggered by severe squalls out ahead of a cold front.  Currently the warnings are in effect to as late as 5 am but there is a chance that more alerts will be issued tomorrow as the front moves further in to Florida.

Other parts of our Country are experiencing severe weather with a different system – e.g. Alabama, Tennessee.

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Spring Is About to “Spring!”

In the Northern Hemisphere this year’s Spring begins on March 20, 2009 at 11:44 Universal Time or 7:44 AM Eastern Standard Time.  Therefore, the first FULL DAY of Spring is March 21, 2009.  On those two days the length of daylight and darkness will be almost exactly the same at 12 ‘n 12.  Of course, if there is a mountain up close to you, either east or west (or both) your daylight hours are more likely to be shorter than your darkness hours even though the time will be close to the Vernal Equinox.

Those of you who drive toward the east early in the morning to get to work and then toward the west to return home in the evening might have been noticing lately that you have been having the sun’s light directly in your eyes on both occasions.  Expect that for a while longer and be careful.

I live 18 miles inland from the Gulf of Mexico at 29 degrees North latitude.  We’ve been here since early August, 2005.  I tell people that I escaped South Florida to return to the United States of America but remained in the low latitudes (barely).  The plants here are blooming like crazy!  My notion is that because they were stressed a great deal from repeated freezing episodes, Mother Nature has been telling them to procreate profusely for survival’s sake.

I took a few snapshots recently and thought I’d share them with you.  Most folks who photograph their flowering plants tend to stand back to get the whole structure but I prefer to get in close enough to see features of some of the individual blossoms.  Like people, they are each beautiful in their own way.  Most of the images in this posting are of azaleas but I did throw in a couple of loropetalum or “fringe flower.”  At the end I was unable to resist showing one of a complete bush behind two oaks.  Today the plants are even denser with blossoms than when I took the photos just a few days ago.

In time, once they’re out, I hope to show you dogwood, crepe myrtle, agapanthus, lilacs, and roses – all on our heavily wooded property.  And, if I’m lucky, the wisteria, which has been struggling in the shade, will bloom this year.

To enlarge the images fully, left click once, pause, and then left click again.

Enjoy!

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ANOTHER FREEZE EPISODE IN MUCH OF FLORIDA

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In the infrared satellite image above the cold front that raced through Florida on Saturday is clearly visible via the cloud pattern over the Atlantic.  It travels through Maine and continues southward toward Hispaniola.  It appears that there is a linear trough over Atlantic waters closer to Florida.

There are freeze warnings for many counties of northern and central Florida tonight.  Please consult your media weather reports or on-line resources  for details.  Expect the coldest temperatures of the week to occur from approximately 6:30 to 7:30 am on the morning of Tuesday, March 3.

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Pilot Error May Have Caused Crash Near Buffalo

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What so many have been reluctant to say – probably being extra cautious because nothing is certain at this time – was finally printed in yesterday’s Wall Street Journal.  In my first posting about this terrible aircraft accident I suggested that if icing was indeed the problem – the accident should never have occurred.  Now – it is beginning to look as though the “reaction” to icing might have been incorrect causing the aircraft to immediately stall.

Please be mindful of the fact that the investigation of this accident is still in a very early stage.  Here is a link to the WSJ article:

http://online.wsj.com/article/SB123492905826906821.html

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RECORD LOWS COMING FOR PARTS OF FLORIDA

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RECORD LOWS ARE EXPECTED FOR PARTS OF FLORIDA ON FRIDAY NIGHT AND SATURDAY MORNING.  I AM EXPECTING BELOW FREEZING WEATHER WHERE I LIVE IN NORTHEAST CITRUS COUNTY.  PLEASE GO TO THE FOLLOWING SITE FOR MORE DETAILS:

http://www.srh.noaa.gov/images/tbw/pdf/TopNews/RecordColdFeb21.pdf

THIS POST AND THE LINK ABOVE ARE TIME SENSITIVE.

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Icing Once Again Is Primary Suspect in Bombardier Dash 8 Q400 Crash

The cause of last Thursday’s terrible airplane crash near Buffalo, New York may never be know for sure.  In any case, such investigations take many months.  There was a brief period of time when there were some significant doubts as to the role of icing in the accident – partly due to the embryonic stage of the investigation hindered by the complexities of carefully sorting debris of the aircraft and the house from the remains of the victims.  What a difficult job that must be.

Yesterday and today there have been more indications that icing was responsible.  If anything accurate can be said about the nature of the environment which produces icing conditions it is that it is fickle.  Just as the surface has its own micro-climatology, so do clouds.  It appears to me that the plane that crashed must have entered an icing environment which might have been severe.  There is also a possibility of some form of mechanical and/or instrument failure.  The final determination could very well point to a combination of unfortunate happenings.

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ICING AS PART OF THE HYDROLOGIC CYCLE – SOME BASICS

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THE HYDROLOGIC CYCLE, A CLASSICAL TOPIC

IN NATURAL SCIENCE COURSES

I’ve taught the hydrologic cycle many times in geology, meteorology, physical oceanography and environmental science classes.  It’s always been a pleasure but I’ve never had enough time.  All of these were college courses and in almost every case the text book covered the subject adequately.  However, the manner in which water moves and changes in our natural environment is so very interesting that a few pages in a text with a traditional drawing and an hour lecture from me simply does not do the subject justice.  Water is such a remarkable compound – I can’t find the words to explain how very interesting it is and how mysterious it can be at times considering the amount of scientific attention it has received through the years.  There is still so much to learn.

So, it is with excitement that I look forward to a 6-hour course that I am scheduled to teach in May to the Senior Institute enrollees at Central Florida Community College.  In 37 years of full-time college teaching (and 4 years part-time) I never had the opportunity to devote so much time to the subject.  The method I intend to use is my own “idea” but surely it has been done before – that is, to follow water step-by-step as it goes from one phase or one environment to the next.  My presentation won’t be a journey without side trips and backtracking.  There are multiple manners in which water can transform and/or move with interesting little anomalies along the way.  With 6 hours to utilize I will be able to discuss aspects that were only fleetingly mentioned in my previous hour-long presentations e.g.: Capillary action, deposition, glacial calving, influent groundwater movement, juvenile water, super-cooled droplets, and much more.

SUPERCOOLED CLOUD DROPLETS AND ICING

I feel fairly certain that some people who read this have had the experience of having rain freeze upon impact with their vehicle’s windshield.  Some would assume that the freezing occurs because the windshield is so very cold.  That is usually not the case.  Instead, the liquid droplets were probably at a temperature well below “freezing” and the impact with the windshield itself triggered the instant freezing.  Hopefully, the “defrosting” vents can keep the windshield warm enough so that the ice can be quickly cleared.  Now, imagine what it must be like if the surfaces being iced are the windshield and wings of your aircraft in flight – as well as other aircraft surfaces (e.g. propellers, fuselage, horizontal stabilizers)!

Today, February 15, 2009, the mere thought of super-cooled droplets hauntingly reminds me that in addition to the marvelous beauty of water’s multifaceted journeys and transitions through our natural environment, there are some insidious elements that can become deadly in this modern world.  Of course, I’m thinking specifically of the recent terrible aircraft accident responsible for 50 fatalities near Buffalo, New York.

PURE SPECULATION

For a short while since the accident it appeared that icing might have been the culprit or perhaps a contributing factor in causing the aircraft to make its sudden rapid descent (apparently almost immediately after the application of flaps).  At the time other aircraft in the vicinity were reporting icing.  HOWEVER, AT THE TIME OF THIS WRITING, NEWS RELEASES HAVE INDICATED THAT THE NATIONAL TRANSPORTATION SAFETY BOARD CLAIMS THAT ICING APPEARS NOT TO HAVE BEEN A FACTOR. The changing of the airfoil’s shape upon flap engagement might have triggered the rapid descent – an apparent stall leading to a flat spin.  That would indicate either insufficient air speed at the time of flap deployment or some type of catastrophic failure.   SINCE MANY AVIATION ACCIDENTS HAVE BEEN CAUSED BY ICING – AND IT WILL REMAIN A PROBLEM FOR AIRCRAFT FOR A LONG TIME TO COME, I SHALL CONTINUE.

When icing was being blamed, I suspected that some critical errors might have been made in the cockpit.  At best, my notions were intuitive – or, on the other end of the spectrum, unfair during such an early stage in the investigation.  Nevertheless, a surprising amount of information has been made available during this embryonic phase – partly due to the fact that the flight recorders are advanced models and they were in very good shape.  There is no need for me to dwell on factors that can cause a plane to become unstable when icing occurs – suffice it to say that airfoils lose “lift efficiency” quickly when ice buildup changes their shape and of course the weight of the ice accumulation can also be a huge factor.  I do not know what kind of air speed indicators are installed on that type of aircraft but I do know that icing can cause false readings on some types.  Icing can also cause problems at air intakes and oil cooler intakes of some aircraft.

BUT WHY DOES THE PHENOMENON OCCUR

IN THE FIRST PLACE?

The cause of the icing is a surprise to most people.  Though icing can occur on a plane’s very cold surface when it descends into “warm” clouds whose temperatures are above freezing, the vast amount of problematic icing occurs when the liquid droplets themselves are below what we traditionally consider freezing temperature.  These droplets consist of what is called supercooled liquid water (SLW).  Water in cloud droplets can get as cold as about negative 40 degrees Celsius (which is the same as negative 40 Fahrenheit) without freezing.

When liquid water freezes (box 3 to 4 in the illustration above) the water molecules align in a crystalline fashion.  But in order to do so they need one of two things:  1) either a freezing nuclei whose surface acts as a template to initially “show” the molecules how (or trigger the molecules to) line up, or 2) some molecules themselves must be jolted (or jiggled) such that for at least an instant they are arranged so they can act as a template or model for the rest to follow.  The likelihood of such alignment occurring in undisturbed droplets is slim.  This would not be true of most fresh water at the surface, such as in lakes because there are microscopically-sized particles available in the water to act as templates.  On the other hand, water that has condensed and remains in the air is very “clean” by comparison.

An aircraft flying though supercooled cloud droplets causes considerable rapid stirring to set the stages for freezing upon impact with that aircraft – just as supercooled raindrops freeze upon impact with trees and suspended wires in those notorious, damaging ice storms.

VIDEO DEMONSTRATIONS

The first three links below show convincing demonstrations of liquid water freezing as a result of hexagonal ice crystal seeding.  The ice crystals provide the template which “shows” the liquid water what to do in order to become solid.  In the third example when the water freezes and builds up a small mound on the wooden post, I suspect that the split second ideal alignment of some water molecules (while pouring) provoked the freezing.

http://www.youtube.com/watch?v=Xe8vJrIvDQM

http://www.youtube.com/watch?v=gGpNhBPYNfs

http://www.youtube.com/watch?v=4g1BDpU7ZQo

In this 4^th example you will see that a jolt causing a sloshing of the water in the small amount of air space at the top of the bottle allows for enough water movement so that for an instant a hexagonal orientation occurs among some molecules causing a very rapid “follow the leader” freezing all the way down to the bottom of the bottle.

http://www.youtube.com/watch?v=DpiUZI_3o8s

Just as condensation and deposition give off heat, freezing is also exothermic.  This is probably why some of the water remains in the liquid state.  If the SLW is not very much colder than “freezing” temperature, the heat given off during freezing will cause the remaining liquid to acquire enough heat to teeter over to the liquid side.

Use the search term “supercooled water” on YouTube.com and you will find many other video demonstrations.

WHEN WATER FREEZES IT EXPANDS, BECOMING LESS DENSE.  THIS EXPLAINS WHY SOLID WATER FLOATS UPON LIQUID WATER.

If you compare box 3 and 4 in the illustration in this post, you will see why water expands and becomes less dense upon freezing.  To establish the hexagonal grid necessary for ice, the molecules can’t be as close together as they were when they were in the cold liquid stage.

Information on supercooled liquid water would have eventually been posted here if the Continental Express Flight 3407 disaster had not occurred.  It is regrettable that the accident played a role in my posting this information at this time.  I offer my sympathy to all who have broken hearts over the loss of a loved one and all others adversely effected.

Finally, the information in this post about SLW and icing merely scratches the surface compared to that which is known.  But, that which is not understood is formidable.

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