Archive for the ‘Fronts’ Tag

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:

https://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:

5-17-09loop2238z

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 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.

5-17-09seLoop0328

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.

5-26-09 2100z SurfC.  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.

6-2-09 sea breeze

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.

6-2-09 628pEST rad ed

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.

6-2-09 333p ESTsurf

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.

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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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YET MORE COLDNESS FOR FLORIDA!

Two independent left clicks will enlarge
Two independent left clicks will enlarge

This seems almost like an instant replay!  We Floridians are again playing host to a couple of surges of cold air.  Florida is once again cloudless and the cold air is relatively dry –  therefore the state can’t count on much of a greenhouse effect to slow the loss of heat from the surface.

My neighborhood in northeast Citrus County, Florida can expect freezing temperatures on Wednesday and Thursday morning – and perhaps Friday morning.  As is so often the case, the fickle microclimatology of a neighborhood can be manifested by a wider-than-expected range of low (and high) temperatures.  For example, during a luncheon today a neighbor reminded me that by virtue of his property being on about the highest ground in the neighborhood, his low temperatures end up being not quite as low as those in other parts of the neighborhood.  This is not always the case but it happens the majority of times because on those cold, marginal mornings when the synoptic pressure gradient is weak, the coldest (and therefore densest) air tends to spill downward into the lower vicinities.

My wife and I have given up on covering our ornamentals – deciding a while ago to allow “survival of the fittest” to kick in.  But – many of my neighbors have already covered some of their plants.

This is not a mean-spirited criticism but it is a huge paradox to me that so many will go out of their way to protect a plant that isn’t meant to grow here yet some think nothing of killing a native species of harmless snake that dares to stray on to their property.  I understand the fear – but not the lethal reaction.

If you are “up north” reading this, I imagine that you’d love to be enjoying our temperatures down here.  Everything is relative, is it not?  For example.  I took my daily 3-mile walk earlier today wearing a light-weight sweater over a T-shirt and at the half-way mark the sweater came off!  It has been a delightful day for early February – that’s for sure.

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GLOBAL CIRCULATION ON NEW YEAR’S DAY

LEFT CLICK TO ENLARGE IMAGE
LEFT CLICK TO ENLARGE IMAGE

What a terrific way to start the new year in this weblog – with an image of nearly the whole earth showing cloud patterns over both the daylight half and the darkness half.  The two rows of extratropical cyclones (one over the middle latitudes of each hemisphere) are striking.  Since a very high percentage of the over 6.7 billion people on earth live in the middle latitudes, and since these cyclonic systems and their cold fronts commonly extend into the lower latitudes, you might very well be under the influence of one of these systems this very moment.  They are marching generally from west to east in both hemispheres followed by cold (or cooler) anticyclones.  For example, I live in the low latitudes at 28.972 degrees north and we get several frontal passages.

The Intertropical Convergence Zone is apparent, especially over Africa.  Notice how it is further south now over that continent than during the North Atlantic hurricane season.

HERE’S WISHING YOU ALL A HAPPY NEW YEAR.  That’s just the beginning because my wishes for you are many.  That:  You “know” love and feel both loved and lovable, you are never bored, you have a long gratitude list, happiness is not illusive, you feel as good as possible for your circumstances, life’s pros far outweigh the cons, and you experience peace and good will always.


Tonie A. Toney (Cloudman23)

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NOTES:  Extratropical means “outside of the tropics.”

Middle latitudes are strictly defined as the regions between 30 degrees and 60 degrees latitude (both hemispheres).

Extratropical cyclones differ from tropical cyclones in the following ways.  ET cyclones are “cold core” lows while T cyclones are “warm core” lows.  ET cyclones generally have fronts associated with them, T cyclones do not.  ET cyclones originate mostly in the middle latitudes while T cyclones originate in the low latitudes (0 degrees to 30 degrees).  ET cyclones are asymetrical with decided wind direction changes and measurable temperature changes on either side of the fronts, while T cyclones are more nearly circular.

The Intertropical Convergence Zone is where the Northeast Trades and the Southeast Trades converge.  Years ago it was referred to as the Doldrums and also the Equatorial Low.  Those two outdated terms are still found in the literature and even on line.  Generally, the ITCZ migrates northward during the northern hemisphere warm season and southward during the northern hemisphere cold season.

STORM OFF THE CAROLINAS IS NOT OF TROPICAL ORIGIN

Two independent left clicks should enlarge this image.
Two independent left clicks should enlarge this image.

The storm that is at the North Carolina-South Carolina border may look like a hurricane but it is not. The National Weather Service is calling it a non-tropical cyclone. A more common term for such cyclones is “extratropical cyclone.” “Extra” means “outside of.” This refers to their developing outside of the tropics. Hurricanes are tropical cyclones. Even though in the northern hemisphere they both rotate counterclockwise around a central region of low pressure, tropical cyclones have warm cores and are often referred to as “warm core lows.” Relatively cold air occupies part of most extratropical cyclones and this is most certainly the case with this one. The doublet image of the system that I have prepared which you see (above) shows a visible satellite view of the storm earlier today and compares it with a surface analysis.  The two do not represent exactly the same time but it’s close; 44 minutes separate them. So, it’s a near match.

For those of you who know your frontal symbols, notice that there are three different types of fronts, all three representing boundaries between relatively warm air and relatively cool air. An occluded front arcs out from the center of the storm and there is a warm front whose axis runs ENE-WSW, and a stationary front curving down to the south.

In spite of the fact that it is extratropical and therefore un-named, it has many of the characteristics of a tropical storm.  People located in the storm’s vicinity should be alert to the potential hazards. Also, there is a strong chance that it will interact with tropical storm Kyle in the interesting Fujiwhara effect.  If you are interested in that phenomenon, see the following link and also view the post that followed it (at the next higher post location on the page).  To do that you will need to scroll to the top of the page and click on the “blog” tab.  That will access you to all entries.

Tropical Wave AL 93 Might Dance Within a Few Days!

Ike’s Widespread Existence – Even Now! – A Radar Image

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TWO LEFT CLICKS OF THIS NATIONAL WEATHER SERVICE RADAR IMAGE WILL ENLARGE

This recent image (above) from 9:38 AM EDT shows the widespread influence of the remains of Ike.  No longer a hurricane, Ike has taken on extratropical characteristics with frontal involvement.  “Extratropical” means “outside of the tropics.”  The synoptic chart below, depicting 8:00 AM EDT does a good job of showing the frontal involvement.  TWO INDEPENDENT LEFT CLICKS WILL ENLARGE.