Area Forecast Discussion
Issued by NWS Key West, FL

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FXUS62 KKEY 031938

Area Forecast Discussion
National Weather Service Key West FL
338 PM EDT Mon Aug 3 2020

The main forecast highlight will be a rise to above normal rain
chances by late Tuesday, with the wetter-than-normal period
continuing until Thursday night.

.SHORT TERM...(Tonight through Thursday)

At the surface, a broad col in the flow is located somewhere
southwest of Andros Island this afternoon, with a broad area of
convergence extending north from there. As evidence, southeast
winds are currently observed in the southeast Bahamas, while
southwest winds are observed here in the Keys. Within this area of
convergence, MIMIC PW imagery shows a north-south axis of
extremely moist air, with Precipitable Water (PW) values of 2.1"
to 2.3" in the axis. So this broad area of convergence off to our
east is the main larger-scale focus for lift and and deeper

It will move little through tonight. It is basically stuck under
southerly flow aloft between a strong subtropical high out near
Bermuda, and an unseasonably south-digging mid-latitude trough in
the Lower Mississippi Valley. It will finally budge slowly
westward across the forecast domain on Tue and Wed, exiting west
into the Gulf on Thu. In its wake, a strong subtropical high will
first nose into the Bahamas on Tue, then nudge across the FL
Peninsula on Wed, finally strengthening and sharpening on Thu.
During this time, above normal rain chances are forecast across
the Keys, with the official forecast reflecting peak chances
coming on Wednesday.


.LONG TERM...(Thursday night through next Monday)

A most seasonable pattern will return from Friday through Monday.
The subtropical high extending from Bermuda to the Bahamas will
expand westward as a ridge across the Florida Peninsula, bringing
seasonable deep- layer east-southeast flow across the Keys. PW
values will dry out back to near normal. The prevalence of high
pressure means we will rely on mesoscale focusing mechanisms, such
as daytime heating on nearby land masses. Have held close to
climo PoPs from Thursday night through Monday.


A broad and ill-defined trough will move west across the waters
on Tuesday, marking a slow transition from southwest back to
southeast winds. This transition will come with periods of light
and variable winds.

A dull ridge will start to build west across the FL Peninsula on
Wed, then sharpen and strengthen on Thu. It will persist into the
weekend. By late in the week, this will lead to gentle to moderate
easterly breezes.


Radar shows a few cloud line showers over the Bayside and Gulfside
waters of the Lower and Middle Keys. These will dissipate by
sunset, leaving a quiet evening. A few showers will start to
bubble up over the nearby waters of the Florida Straits overnight
and persist into Tue morning, leading to insertion of VCSH for
the MTH and EYW TAFs starting during the overnight hours. Outside
of convective activity, VFR conditions will prevail the large
majority of the time, with fair weather cumulus bases in the
018-030 range.


Key West  82  90  81  89 / 20 30 40 50
Marathon  81  89  81  89 / 30 30 40 40




Data Acquisition.....DR

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