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240
FXUS62 KKEY 201834
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
234 PM EDT Thu Jun 20 2024

...New DISCUSSION, MARINE, AVIATION...

.DISCUSSION...
-- Changed Discussion --
Issued at 230 PM EDT Thu Jun 20 2024
The Florida Keys remain entrenched in a complicated synoptic-
scale pattern. In the upper-levels, CIMSS satellite-derived
vorticity product highlights a closed low centered just to the
southwest of the upper-levels. Meanwhile, in the lower
troposphere, a tropical wave now centered over the northern
Bahamas continues to propagate west northwestward towards northern
Florida. Surface analysis reveals a weak low pressure system
centered near the same location, Tropical Depression Alberto over
eastern Mexico continuing to weaken, and a sprawling area of high
pressure centered just north of Bermuda bifurcating these
features. GOES-16 visible satellite imagery clearly highlights the
broad cyclonic (counterclockwise) composite flow straddling the
Florida Keys. Skies are partly to mostly cloudy across the Florida
Keys and the adjacent nearshore and offshore coastal waters.
Earlier scattered shower and thunderstorm activity has generally
waned over the past several hours, as a wave of relatively dry air
evident on water vapor imagery upstream of the Keys continues to
filter westward. Temperatures are generally in the mid to upper
80s at the island communities.

A challenging forecast will continue over the next several days,
as the features described above interact. In addition, another
Central American Gyre (CAG) cell is progged to develop over the
Yucatan peninsula tomorrow, then slide northwestward into the Bay
of Campeche early next week, pushing tropical moisture in our
vicinity. All of these features will tend to elevate rain and
thunder chances well above climatology. However, an examination of
satellite- derived layer- averaged total precipitable water
products suggest spokes of dry air from higher latitudes will
occasionally propagate into the CWA. The first of this has begun,
and visible satellite imagery shows mostly clear skies upstream in
the vicinity of the Bahamas, including Andros Island. Given this,
near-normal rain and thunder chances appears appropriate for
tonight.

Friday looks like a transition day, as more moist air progresses
into our coastal waters from the east. Forecast soundings for late
Friday through Sunday show deep, tropical moisture for this time
frame, with the aforementioned upper-level trough lurking in the
vicinity. Given this scenario, nearly every shower will have the
chance to achieve thunderstorm status, and thus have elected to
raise thunder chances to the elevated category for these forecast
periods.

The upper-level trough will gradually weaken as it slides
southward out of our coastal waters on Sunday. This will be in
tandem with the CAG cell dissipating. A climatologically-
consistent area of high pressure will build over the North
Atlantic. In this scenario, rain chances should return to near
normal, driven by any tropical troughs and associated moisture
undulations pushing into our area from the east southeast. Due to
cloud cover, temperatures will be at or just below normal through
the weekend, gradually rebounding to near normal for much of next
week.
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&&

.MARINE...
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Issued at 230 PM EDT Thu Jun 20 2024
Small craft should continue to exercise caution for all
Florida Keys coastal waters overnight except the Florida Bay,
with easterly winds 15 to 20 knots. From synopsis, strong high
pressure centered north of Bermuda working in tandem with Tropical
Depression Alberto over eastern Mexico will result in moderate to
fresh breezes through this evening. A second, weak area of low
pressure currently near the northern Bahamas will continue to move
west northwest, reaching the southeast U.S. by early Friday
morning. The interaction of these features will loosen the
pressure gradient, leading to slackening east to southeast breezes
for Friday through the weekend. High pressure building over the
North Atlantic early next week will result in light to gentle
southeast to south breezes.
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&&

.AVIATION...
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(15Z TAFS)
Issued at 230 PM EDT Thu Jun 20 2024
VFR conditions will prevail at both EYW and MTH through the TAF
period. Shower activity will return early this evening so VCSH is
included from 20z onward. Near surface winds are easterly at near 15
knots with gusts at times of up to 25 knots.
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&&

.CLIMATE...
On this date in 1983, an F1 tornado produced $2.5m in damage near
Lower Sugarloaf Key. There were no tropical cyclones in the area.

&&

.PRELIMINARY POINT TEMPS/POPS...
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Key West  88  79  88  79 /  50  30  40  50
Marathon  88  80  88  80 /  40  30  40  50
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&&

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...None.
&&

$$

Public/Marine/Fire...BT
Aviation/Nowcasts....AP
Data Acquisition.....DR

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