Area Forecast Discussion
Issued by NWS Key West, FL

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FXUS62 KKEY 210850
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
450 AM EDT Mon Sep 21 2020

.DISCUSSION...
.CURRENTLY...
Under mostly clear to partly cloudy skies and light northeast
winds of 5 to 10 mph, temperatures are primarily in the lower
80s along the island chain. Meanwhile, local radars are only
detecting isolated showers and thunderstorms, with the majority of
the cells on the Straits of Florida out 30 nm from the Island
Chain. On our marine district, winds are northeast ranging from 4
knots at Sand Key Light to 11 knots at Carysfort Reef Light.

&&

.SHORT TERM...(Today through Wednesday)
A pronounced mid and upper level vorticity lobe extending from a
trough of low pressure offshore of the mid Atlantic States, and
across extreme South Florida into the Northwest Gulf of Mexico
early this morning, will drop southwestward and cross our region
late this afternoon through most of tonight. Given formidable mid
and upper level ascent associated with a significant and
confluent northeast to east flow will result in likely to
categorical rain chances late this afternoon through after
midnight. In wake of this disturbance aloft, drier air will filter
into our region leaving a convergent flow so scattered coverage
will be carried after midnight. Only a slight chance will be kept
for Tuesday through Wednesday. Otherwise, with the breezy to
windy northeast to east trajectory coming off the Continental
United States, fairly comfortable conditions with drier and
slightly cooler air can be expected.

&&

.LONG TERM....(Wednesday night through Sunday)
A trough of low pressure in the Northwest Caribbean Sea along with
a ribbon of mid and upper level ascent will move slowly northward
and into our region by the end of this week and next weekend.
Given an increase in moisture, subtle ascent and low level
convergence, periodic above normal rain chances will be retained.
Steamy and above normal rain chances will return.

&&

.MARINE...
Due to an increasing north swell building to as high as 12 feet
on the Straits of Florida offshore of the Upper Keys, a Small
Craft Advisory will remain in effect through at least Tuesday.
Elsewhere, an Exercise Caution headline will be needed by late
this afternoon for the Reef Tract offshore of the Upper Keys and
Florida Bay by late this afternoon. However, strong northeast to
east winds will overspread our entire marine district tonight when
a Small Craft Advisory will be required. In addition, showers and
thunderstorms will be on the increase from north to south late
this afternoon and especially until around midnight. With that,
winds and seas will be even higher near the strongest cells and
the speed at which they will be moving. For the balance of this
week, moderate to fresh winds will predominate across our coastal
waters, when an Exercise Caution Headline/Advisory may be
required.

&&

.AVIATION...
VFR conditions early this morning will give way to increasing rain
chances during the day, as a frontal boundary sags southward toward
the Keys. Periods of MVFR conditions will be possible with any
convection at the terminals, but uncertainty as to timing and
duration remains high, so we are carrying just VCSH in the terminal
forecasts until late this afternoon. As the front moves into the
Keys during the evening hours, expect numerous showers and scattered
thunderstorms to impact the terminal areas, with a strong likelihood
for periods of MVFR/IFR conditions along with gusty ENE winds. Have
indicated prevailing -SHRA, VCTS and TEMPO for MVFR conditions
during the evening hours. Light NNE winds will become NE and
gradually increase during the day, then increase sharply in the late
afternoon to early evening hours as the front moves through. Strong
ENE winds of 15 to 20 knots with gusts up to 30 knots are likely
during the evening and overnight hours. Even stronger wind gusts
will be possible with passing showers and storms.

&&

.CLIMATE...
In 1890, the daily record low temperature of 70 degrees was
recorded in Key West. Temperature records date back to 1872.

&&

.PRELIMINARY POINT TEMPS/POPS...
Key West  86  78  86  80 / 50 + 20 20
Marathon  86  77  87  79 / 50 + 20 20

&&

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...Small Craft Advisory for GMZ052-072.

&&

$$

Public/Marine/Fire...APA
Aviation/Nowcasts....Jacobson

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