672
FXUS62 KKEY 190251
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
1051 PM EDT Mon Aug 18 2025

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

.DISCUSSION...
Issued at 1050 PM EDT Mon Aug 18 2025
An upper-level composite analysis this evening reveals two
dominant features on the synoptic scale: 1) Hurricane Erin over
the Atlantic just east of the Bahamas, and centered near the
latitude of the Florida Keys; and 2) a deep layer mean
anticyclone centered over the mid-Mississippi River Valley. The
presence and location of these two systems relative to the Florida
Keys and adjacent coastal waters has resulted in a mean lower-
tropospheric layer mean wind from the NNE over the service area.
As a consequence, showers and thunderstorms and their associated
outflow boundaries that initiated along sea, bay, and lake
breezes over mainland South Florida have moved south-southwestward
over Florida Bay and the Gulf waters north of the middle Keys,
with additional showers initiating along subsequent outflows over
portions of the Keys and now across Hawk Channel and the Straits
of Florida. Some of the storms were rather strong over the
mainland Everglades during the late afternoon hours, but cells
weakened modestly over the coastal waters.

Data from the Key West evening radiosonde balloon indicated a
typical moderately unstable atmosphere with weak inhibition. It
was quite dry above about 5,000 feet. Nevertheless, subcloud
moisture was rich and sufficient for deep cumulus convection, as
we have seen. In any case, overall rainfall coverage has been
limited, both in Florida Keys island communities and offshore.

Currently, air temperatures in Keys island communities are holding
in the mid to upper 80s, with dewpoint temperatures in the mid to
upper 70s yielding heat indices near or just under 100F. Breezes
are light but somewhat variable in direction, coming in mostly out
of the northwest, north, or northeast.

For overnight, the convection allowing models indicate a continued
decrease in both coverage and intensity of cells.
&&

.MARINE...
Issued at 1050 PM EDT Mon Aug 18 2025
No watches, warnings, or advisories are in effect for Florida Keys
coastal waters. Major Hurricane Erin will track parallel to the
Bahamian Isles overnight, before turning due northward over the
open Atlantic on Tuesday. The increasingly expansive circulation
of Erin will result in a transition from light to gentle northerly
breezes across Florida Keys coastal waters overnight, to gentle
to moderate northwest breezes Tuesday and moderate to fresh
westerly breezes on Wednesday. As Hurricane Erin migrates farther
away toward the north and northeast, a weak subtropical high
pressure ridge will settle over Florida Keys coastal waters,
resulting in a lighter wind pattern Thursday through Saturday.
Finally, long-period swells (10-13 seconds at 3-5 feet) generated
by Hurricane Erin will reach the Straits, especially off the
upper Keys by Tuesday night-Wednesday.
&&

.AVIATION...
(00Z TAFS)
Issued at 1050 PM EDT Mon Aug 18 2025
Through 19/24Z, prevailing VFR conditions are expected at both EYW
and MTH. Isolated showers and thunderstorms will develop along
mainland FL sea breezes after 19/18Z, with movement vectors from
about 350/12 knots, thereby potentially leading to cells in the
vicinity of or near both EYW and MTH. However, probabilities of
sub-VFR conditions are too low for inclusion in TAFs.
&&

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

$$

Public/Marine/Fire...Kasper
Aviation/Nowcasts....Kasper
Data Acquisition.....AJP

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