Archive for the ‘Florida's Rainy Season’ Category
Enlarge images in this posting with left clicks.
ILLUSTRATION B – map of Citrus County showing locations of the Gulf Coastal Lowlands which are subject to storm surges, the sandy Brooksville Ridge occupying more than one-third of the area, and the Tsala Apopka Plain containing the majority of the county’s fresh water lakes –
– TWO INDEPENDENT LEFT CLICKS ENLARGE THE IMAGE ABOVE TO THE FULLEST –
I Am Very Happy Living In Citrus County.
Of course, being retired, being a nature-lover and being relatively healthy helps. All locations have pros and cons but with respect to the latter I have yet to regret the move with my extended family 9 years ago. We had experienced hurricanes and tropical storms through the years. Our house was a total loss in 1992’s category 5 hurricane Andrew; it was at ground zero in Homestead which is located 27.6 miles (as the crow flies) southwest of Miami. The house belonging to my wife’s folks, less than a mile away, had extensive damage. What a terrible mess was caused by the only hurricane to make landfall upon the U.S.A. that season. But when we moved to Citrus County 13 years later we were conscious of the fact that by leaving South Florida we had NOT left “hurricane country.” I felt that Citrus County would be safer in that respect but certainly not a hurricane-proof location. It didn’t take long for me to meet people who felt that there was something special about Citrus and other nearby counties that made a serious hurricane event almost inconceivable.
Complacency is a real problem in hurricane country. I don’t claim to be an expert on complacency but there have been times in my life where I might have contracted the disorder I call “terminal uniqueness.” Therefore, I am acquainted with denial, ignorance, procrastination, irresponsibility, and “living in a dream world” because I’ve been there; for all I know, I’m there still. I believe that every time I point a finger at someone, three are pointing back at me and this is written in that spirit. Thus, I’m not trying to indict anyone here; I’m just trying to state what appears to me to be true.
As I see it – Citrus County, as a whole, though probably not the “geographical poster child” for complacency when it comes to hurricanes and tropical storms, seems to be after the title – in spite of its experience with “The Florida Four in 2004” (see illustration C below). I’m not speaking of those who vigorously engage in emergency planning and increasing awareness in the community. And of course I’m not speaking to residents reading this who have engaged in effective advanced planning and preparation. No, I’m speaking of the average Jack and/or Jill occupying a dwelling in Citrus County; I acknowledge that there are plenty of exceptions. To be sure – this is not a problem exclusive to Citrus County. I believe it’s prevalent in all or nearly all parts of the country susceptible to tropical cyclonic weather. Please click on this graphic below for enlargement.
The four 2004 storm tracks above are dated for your convenience. For example: Tropical storm Bonnie’s track runs from August 3rd to August 14.
NOTE: For an infrared satellite loop of the majority of the 2004 season, click on the first link below. Date and time indicators appear along the bottom margin. Then for an animated loop which is easier to interpret click on the second link.
I moved to Florida in 1956 during my high school junior year and I don’t remember a time since when I have not been conscious of the potential for tropical weather to wreak havoc upon lives and property and I have always tried to be prepared. If you were to have simply driven by my house you could have observed elements of hurricane preparedness. That is still true today. It is a high priority item in my family. I have been an active advocate of hurricane awareness and preparation for many years. If anything, I hope that illustrations in this weblog posting will increase awareness at least among the few who see it. So let me call your attention to the illustration below. Most residents who see such illustrations are, at the very least, surprised. Naturally some point out that this covers a long period of time. But really, is 161 years a long time in the whole scheme of things? My point in showing this is: TROPICAL CYCLONES ARE A REALITY IN CITRUS COUNTY. Also, please be aware of the fact that the plot lines show the paths of the centers of storms and that the storms have a width that is not apparent here. The center of a storm does not have to come within just a few miles for it to be of great concern; the center can be many miles away.
Even before leaving Homestead for good in 2005 – while visiting Citrus County I detected the existence of a notion of immunity to any sort of serious tropical cyclonic weather (e.g. hurricanes, tropical storms). Though I have no scientific evidence to back this – I classify the “no-need-to-be-concerned” feeling as widespread among the Citrus County population. In fact, sometimes “low-to-no” hurricane probability has been drastically overstated here (I’ve heard it and I’ve heard about it). It seems that “The Florida Four in 2004 ” did very little to squelch the delusion. Still – I would have expected that particular season to have provided a huge “wake up call.”
NOTE: The “official” Florida Four in 2004 includes hurricane Charley which struck Punta Gorda on August 13 and later moved through South Carolina. It does not include tropical storm Bonnie.
Just a few weeks ago I overheard a hostess at a popular restaurant in adjacent Marion County telling a booth full of patrons, “We just don’t get hurricanes here.” Recently a friend of mine suggested that there was something about our county’s geography, specifically the Brooksville Ridge, that prevented hurricane visits. That reminded me of Muncie, Indiana where I used to live; it is alleged to be immune from tornadoes because of a particular bend in the river flowing through it. Also, a protective blessing from an Indian chief has been cited.
“The Florida Four in 2004” did not produce the extent of damage or flooding that raised eyebrows all over the nation and, for now, a sense of security from lethal storms seems to cling on. This is not a prediction nor is it my wish, but I do fear that a hurricane coming through this area has the potential to surprise a lot of people and make them wonder what they were thinking. And such an event could be deadly and most certainly destructive.
Storm Surge Potential
When I was looking for property in Citrus County one of my big concerns was the encroachment of wind-driven sea water with a storm – the so-called storm surge. Upon investigation I found what I expected – that if it was important to me personally to avoid surge potential I should avoid about one-third of the county’s land area – the western third.
NOTE: Illustration B, “map of Citrus County” might be useful to you here.
Most of that western third is undeveloped but there are two noteworthy communities within it, Homosassa and most of Crystal River. Therefore, early on I decided not to settle on the Gulf Coastal Lowlands but instead chose the Brooksville Ridge. In my opinion, the broad, hilly, sandy ridge is, by far, the safest place for a home or business in the county because of it’s higher elevations and greater ability to handle large amounts of precipitation often associated with a storm. The highest point in the county is within the Citrus Hills Golf Course above a 230′ contour – my Google Earth measurement has it at 235 feet.
ILLUSTRATION E – Storm surge portion of Citrus County, the western third (color-coded). T = tropical storm and the numbers represent hurricane categories. Left click to enlarge or go to the next illustration for more detail.
FOR STORM SURGE ZOOM CAPABILITIES, click on this link:
To be fair, Citrus county seems not to have been visited by category 5 or 4 hurricanes though at nearby Cedar Key a 1896 hurricane was a category 4 according to some estimates – crediting it with 135 mph winds.
NOTE: As far as we know, only three Category 5 storms have struck the U.S.A. – the 1935 Florida Keys or Labor Day hurricane, Hurricane Camille which hit Mississippi in 1969, and 1992’s Hurricane Andrew. The records aren’t good enough to say whether any earlier storms were Category 5 by today’s standards and they don’t go back very far with respect to the length of time that such storms have visited the North American mainland.
But lesser tropical cyclones, like tropical storms and tropical depressions, can produce both microbursts and tornadoes and simple straight-line gusts can far exceed the sustained wind velocity of such storms. Of course this is true for hurricanes too. Illustration G below shows initiation points of tornadoes spawned by tropical cyclones (e.g. tropical depressions, tropical storms, hurricanes) from 1995 through 2010. The entire report is available in the PDF format here:
– ILLUSTRATION G –
Please enlarge this with a left click. This illustration is on page 7 of Roger Edwards’ report which is available to you as the previous PDF document link titled Tornadoes Tropical Cyclones.
Recently, I looked into the proximity of past storms near my church and created a graphic for those who might be interested. Since the church is located in Lecanto and near the geographical center of Citrus County, I’m including the graphic in this weblog entry. Notice that I picked a small radius of 25 miles yet the illustration clearly shows a lot of activity. Had I picked a larger radius, say 50 miles, the graphic would show many more storms ( for an example of what I mean, see illustration D with a 100 mile radius centered on Inverness).
– ILLUSTRATION H –
Note: If you would like to utilize the program I used to derive illustration D and illustration H, here is a link:
The Relationship Between Wind Velocity and Its Potential Force
There is one last point I’d like to make and I have found in my years of teaching that there are many people who do not know this: One would think that the potential force of an 80 mph wind would be twice that of a 40 mph wind. But that is not true. The relationship is not linear – it is exponential. An 80 mph wind has FOUR TIMES the potential force of a 40 mph wind. When someone looking at the historical chart above sees mostly tropical storms (green) and category 1 hurricanes (yellow) they typically tend to minimize the dangers. They don’t realize that an 80 mph category 1 hurricane wind is far worse than a 60 mph tropical storm wind. I’ve done the math and, as it turns out, an 80 mph hurricane wind has 1.78 times the potential force of a 60 mph tropical storm wind (or close to twice the potential force). So, in even more simple terms, small increases in wind velocity result in large increases in potential force! For more discussion on the relationship between velocity and force, click on this link to a previous weblog entry:
My next mission is to discuss this with some people in the area to learn their attitudes and feelings on the subject. I’m sure I will learn a lot and gain more knowledge and insight. For example, I’ll bet there are some who just don’t feel it’s worth the effort – that they will just evacuate and let insurance take care of things, or maybe take some losses and leave for good if a serious storm messes things up. Others must find permanent window and door protection to be “cost prohibitive” and have plans to somehow temporarily protect those openings – maybe at the last minute. None of those approaches work for me; there are just too many variables. For example, try buying plywood when it becomes fairly clear that a hurricane is coming your way. Or – consider what it might be like if you do plan to evacuate but wait too long and are unable to do so. Being inside a home that is breaking apart during a serious hurricane is no picnic.
NOTE: See link below to “Window Protection Is Essential”.
I suspect that there are many who feel they have thought things through and that their apparent inaction is merely a function of our individual differences in thinking. Perhaps they do indeed have a “plan” albeit different than mine. What’s the saying – “Different strokes for different folks”? Regardless, I strongly recommend advanced preparation.
I observed complacency among many people in pre-Andrew Homestead and suspect it exists there again because, after all, that was 22 years ago. So why should I expect a greater awareness and more obvious preparation along the Nature Coast where Citrus County is located? The fact is, I don’t. But I can dream, can’t I?
Citrus County Emergency Management – http://www.sheriffcitrus.org/EM/
Disaster Preparedness (Florida Department of Health – Citrus County) http://www.floridahealth.gov/chdCitrus/disasterpreparedness.htm
Hurricane misconceptions: https://cloudman23.wordpress.com/2008/09/23/952/
Saffir-Simpson hurricane categories: http://www.nhc.noaa.gov/aboutsshws.php
Sustained winds: http://www.aoml.noaa.gov/hrd/tcfaq/D4.html
Window protection is essential: https://cloudman23.wordpress.com/2008/09/08/window-protection-for-hurricanes-is-essential/
The effects of hurricane winds upon a house: https://cloudman23.wordpress.com/2008/09/10/the-effect-of-hurricane-winds-upon-a-house/
Hurricane focus on Central Florida: https://cloudman23.wordpress.com/2008/09/13/hurricane-focus-on-central-florida/
Why is Florida so humid? https://cloudman23.wordpress.com/2009/07/04/why-is-florida-so-humid/
Below is a “cut and paste” from the National Hurricane Center’s report for the first day of the hurricane season, 2011. There is a low pressure system in the Atlantic now making a beeline for my part of Florida and expected to be here around 1 PM. Item 1 below is the discussion of that system. At the very end of this posting you will find a link to the page from which this information was cut. If the graphic you first see is not the satellite image, just left click on it and it should change for you.
My daughter is visiting from New Mexico and this is the day that she and I were to have gone sailing. However – that activity has been canceled and my “little girl” is sleeping in. There was a time in my life when I was more daring and would have gone out anyway – working hard to strategically find safe shelter and counting on lots of luck. But now in my 72nd year I am one to err on the side a caution. The aluminum mast supported by a steel fore-stay and two steel shrouds all serve as excellent lightning attractors. I do not wish for my daughter (or myself for that matter) to become a “crispy critter.” The fun is not worth the risks. So we will find something else to do. The tiny red dot on the image below approximates where I live in Florida and the system is traveling toward the west-southwest. Left click on the image to enlarge.
From my point of view, this is a fitting “sign” that our hurricane season this year is likely to be a busy one. The post that follows this one will link you to a description of the NOAA summary of this years forecast.
ZCZC MIATWOAT ALL TTAA00 KNHC DDHHMM TROPICAL WEATHER OUTLOOK NWS NATIONAL HURRICANE CENTER MIAMI FL 800 AM EDT WED JUN 1 2011 FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO... 1. A SMALL AREA OF LOW PRESSURE LOCATED ABOUT 200 MILES EAST OF JACKSONVILLE FLORIDA IS MOVING WEST-SOUTHWESTWARD AT AROUND 20 MPH. THE LOW CONTINUES TO PRODUCE A CONCENTRATED AREA OF SHOWERS AND THUNDERSTORMS...AND ENVIRONMENTAL CONDITIONS ARE MARGINALLY FAVORABLE FOR SOME DEVELOPMENT OF THIS SYSTEM BEFORE IT MOVES OVER NORTHERN FLORIDA LATER TODAY. REGARDLESS OF DEVELOPMENT...THIS DISTURBANCE COULD PRODUCE LOCALLY HEAVY RAINFALL AND STRONG GUSTY WINDS OVER PORTIONS OF THE FLORIDA PENINSULA. THERE IS A MEDIUM CHANCE...30 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS. FOR ADDITIONAL INFORMATION ON THIS SYSTEM...PLEASE SEE PRODUCTS FROM YOUR LOCAL NATIONAL WEATHER SERVICE OFFICE. ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE NEXT 48 HOURS. TODAY MARKS THE FIRST DAY OF THE ATLANTIC HURRICANE SEASON...WHICH WILL RUN UNTIL NOVEMBER 30. LONG-TERM AVERAGES FOR THE NUMBER OF NAMED STORMS...HURRICANES...AND MAJOR HURRICANES ARE 11...6...AND 2...RESPECTIVELY. THE LIST OF NAMES FOR 2011 IS AS FOLLOWS: NAME PRONUNCIATION NAME PRONUNCIATION ------------------------------------------------------------- ARLENE AR LEEN- LEE LEE BRET BRET MARIA MUH REE- UH CINDY SIN- DEE NATE NAIT DON DAHN OPHELIA O FEEL- YA EMILY EH- MIH LEE PHILIPPE FEE LEEP- FRANKLIN FRANK- LIN RINA REE- NUH GERT GERT SEAN SHAWN HARVEY HAR- VEE TAMMY TAM- EE IRENE EYE REEN- VINCE VINSS JOSE HO ZAY- WHITNEY WHIT- NEE KATIA KA TEE- AH THIS PRODUCT...THE TROPICAL WEATHER OUTLOOK...BRIEFLY DESCRIBES SIGNIFICANT AREAS OF DISTURBED WEATHER AND THEIR POTENTIAL FOR TROPICAL CYCLONE FORMATION DURING THE NEXT 48 HOURS. THE ISSUANCE TIMES OF THIS PRODUCT ARE 2 AM...8 AM...2 PM...AND 8 PM EDT. AFTER THE CHANGE TO STANDARD TIME IN NOVEMBER...THE ISSUANCE TIMES ARE 1 AM...7 AM...1 PM...AND 7 PM EST. A SPECIAL TROPICAL WEATHER OUTLOOK WILL BE ISSUED TO PROVIDE UPDATES ...AS NECESSARY...IN BETWEEN THE REGULARLY SCHEDULED ISSUANCES OF THE TROPICAL WEATHER OUTLOOK. SPECIAL TROPICAL WEATHER OUTLOOKS WILL BE ISSUED UNDER THE SAME WMO AND AWIPS HEADERS AS THE REGULAR TROPICAL WEATHER OUTLOOKS. A STANDARD PACKAGE OF PRODUCTS...CONSISTING OF THE TROPICAL CYCLONE PUBLIC ADVISORY...THE FORECAST/ADVISORY...THE CYCLONE DISCUSSION... AND A WIND SPEED PROBABILITY PRODUCT...IS ISSUED EVERY SIX HOURS FOR ALL ONGOING TROPICAL CYCLONES. IN ADDITION...A SPECIAL ADVISORY PACKAGE MAY BE ISSUED AT ANY TIME TO ADVISE OF SIGNIFICANT UNEXPECTED CHANGES OR TO MODIFY WATCHES OR WARNINGS. THE TROPICAL CYCLONE UPDATE IS A BRIEF STATEMENT TO INFORM OF SIGNIFICANT CHANGES IN A TROPICAL CYCLONE OR TO POST OR CANCEL WATCHES OR WARNINGS. IT IS USED IN LIEU OF OR TO PRECEDE THE ISSUANCE OF A SPECIAL ADVISORY PACKAGE. TROPICAL CYCLONE UPDATES ...WHICH CAN BE ISSUED AT ANY TIME...CAN BE FOUND UNDER WMO HEADER WTNT61-65 KNHC...AND UNDER AWIPS HEADER MIATCUAT1-5. ALL NATIONAL HURRICANE CENTER TEXT AND GRAPHICAL PRODUCTS ARE AVAILABLE ON THE WEB AT WWW.HURRICANES.GOV. SIGN UP FOR PRODUCT UPDATES BY EMAIL AT WWW.HURRICANES.GOV/SIGNUP.SHTML...IN ALL LOWER CASE. YOU CAN ALSO INTERACT WITH US ON FACEBOOK AT WWW.FACEBOOK.COM/US.NOAA.NATIONALHURRICANECENTER.GOV. $$ FORECASTER BERG/PASCH NNNN Here is a link to the National Hurricane Center Home Page: http://www.nhc.noaa.gov/gtwo_atl.shtml
By the time you read this, May of 2011 will have ended and the Northern Hemisphere Atlantic, Caribbean, and Gulf of Mexico hurricane season will have begun. The following link will take you to a summary of the NOAA outlook for this season:
Please be prepared if you live in hurricane territory.
The loop above illustrates nicely that a tropical system does not have to be a hurricane in order to cause significant problems including fatalities. TO ACTIVATE YOU MUST LEFT CLICK ON THE IMAGE. Here is what Wikipedia has to say about the 2008 storm: Tropical Storm Fay was a tropical storm and the sixth named storm of the 2008 Atlantic hurricane season. Fay formed from a vigorous tropical wave on August 15 over the Dominican Republic. It passed over the island of Hispaniola, into the Gulf of Gonâve, across the island of Cuba, and made landfall on the Florida Keys late in the afternoon of August 18 before veering into the Gulf of Mexico. It again made landfall near Naples, Florida, in the early hours of August 19 and progressed northeast through the Florida peninsula, emerging into the Atlantic Ocean near Melbourne on August 20. Extensive flooding took place in parts of Florida as a result of its slow movement. On August 21, it made landfall again near New Smyrna Beach, Florida, moving due west across the Panhandle, crossing Gainesville and Panama City, Florida. As it zigzagged from water to land, it became the first storm in recorded history to make landfall in Florida four times. Thirty-six deaths were blamed on Fay. The storm also resulted in one of the most prolific tropical cyclone related tornado outbreaks on record. A total of 81 tornadoes touched down across five states, three of which were rated as EF2. Damage from Fay was heavy, estimated at $560 million.
Here is a link to Wikipedia’s coverage of that storm:
Here is a link to my list of 23 Misconceptions About Hurricanes:
If you wish to see other posts on this web-log
but are unable,
please click on the “blog” tab
near the top of this page.
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 at least 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.
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:
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.
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.
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).
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 30th 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.
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:
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.
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.
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.
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:
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:
If you wish to see other posts on this web-log but are unable,
please click on the “blog” tab near the top of this page.
A related post, “Why Is Florida So Humid” has been added.
It can be found here:
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:
MOST ALL IMAGES IN THIS WEB-LOG ENLARGE
WITH A LEFT CLICK OR TWO
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 17th 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 17th.
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 10th 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.
Tonie A. Toney
If you wish to see other posts on this web-log but are unable,
please click on the “blog” tab near the top of this page.