202
FXUS62 KKEY 180918
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
518 AM EDT Fri Oct 18 2024

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

.DISCUSSION...
Issued at 517 AM EDT Fri Oct 18 2024
An upper-level composite analysis early this morning reveals a
sharp upper ridge over the eastern United States supporting a
sprawling continental polar anticyclone centered over Pennsylvania
and extending south over the Gulf of Mexico and Florida Peninsula.
A decelerating cold front was analyzed from the central Bahamas
across western Cuba to the northern Yucatan Peninsula. This front
is becoming increasingly diffuse. To its immediate south, a broad
area of low pressure (Invest AL95) was associated with a rich
maritime tropical air mass, which extended to the north and east
along the front. Geostationary satellite animations from the
infrared channel indicate numerous large clusters of deep, moist
convection with mid and high cloud layers spreading north-
northeastward from the western Caribbean. Closer to home, Key West
Doppler base reflectivity data have shown a persistent area of
stratiform rain with embedded deeper convective cells in an east-
west swath along the southern marine zones and western Cuba. To
north of this region, scattered shallow convective cells have
broken out in the strong ENE flow over the Straits of Florida.
Florida Keys island communities have remained rain free and within
the very pleasant modified continental polar air mass amidst
strong NE breezes. Current air temperatures in most Keys island
communities are holding in the mid-upper 70s. Dewpoint
temperatures bottomed out in the mid 60s just before midnight, but
have been ever so slowly creeping upward overnight, and are now
mostly in the upper 60s.

For today and tonight, a windy, cloudy, and occasionally rainy
weather pattern seems likely, with an outside shot at a
thunderstorm. As the AL95 low pressure area churns westward toward
Guatemala and Mexico, most numerical weather prediction models
and recent observational trends suggest that the cold front will
become stationary (it may have already done so), and briefly
buckle northward, resulting in high coverage of (both stratiform
and convective) rain over the service area, with a decent gradient
increasing from north to south. With strong high pressure
persisting north of the Keys, lowering pressure over the western
Caribbean, and a kink in the gradient near the buckling front,
there is some risk for gale-force winds locally; hence, the Gale
Watch for Florida Keys coastal waters.

Saturday through Monday, As AL95 migrates westward over southern
Mexico, a somewhat complicated midlatitude upper flow pattern will
still support a persistent, slowly evolving anticyclone at the
surface over the eastern United States, which will maintain
strong NE breezes. In addition, more uniform NE flow in the
lower/mid troposphere will transport much drier air into the
region, leading to clearing and drier weather.

For Monday night and beyond, the governing surface anticyclone
will weaken slowly, as will the local gradient flow, resulting in
a very gradual decrease in NE or ENE wind speeds. It looks like
the advection of cooler and drier air of continental origin will
be approximately balanced by the upward fluxes of heat and
moisture from the still-warm ocean, resulting in a persistent
temperature/dewpoint pattern, with highs in the mid 80s, lows in
the mid/upper 70s, dewpoints in the lower 70s. Rain chances will
be near or below climatological averages through the end of the
week.
&&

.MARINE...
Issued at 517 AM EDT Fri Oct 18 2024
A Small Craft Advisory and Gale Watch are in effect for all
Florida Keys coastal waters zones. A sprawling autumn high
pressure system over the eastern United States will maintain
strong northeast to east breezes, possibly near gale force
tonight. Breezes will only modestly slacken for early next week,
when fresh to strong northeasterly breezes are expected.
&&

.AVIATION...
(06Z TAFS)
Issued at 517 AM EDT Fri Oct 18 2024
Strong northeast to east breezes will persist throughout the TAF
period at both EYW and MTH. This will likely produce significant
crosswinds. Rain chances will gradually increase through the late
morning hours as showers and possibly a thunderstorm or two develop
along the stalled front in the Straits of Florida and lift north.
Mention is not yet included in either TAF due to high uncertainty in
timing and exact location of precipitation, though recent CAM runs
target a time period near 15z for showers encroaching on the
vicinity of either terminal. Short term amendments will be issued to
address imminent sub VFR impacts due to passing convection.
&&

.CLIMATE...
October 18 has been a busy date in Florida Keys weather
history...

-- In 1944, a Hurricane moved north off of Cuba, passing over the
 Dry Tortugas where the minimum pressure was 28.02 inches of
 mercury and Tropical Storm force winds were reported for 72
 hours, with winds exceeding 120 mph for two hours. In Key West,
 the minimum pressure was 29.14 inches of mercury, with a peak
 wind of 56 mph.
-- In 1841, a Hurricane passed just west of Key West (on the
 18th-19th) grounding many ships, especially at Mango Key (9 mi
 east of Key West).
-- In 1906, a category 3-4 Hurricane moved north-northeastward off
 of Cuba, passing just southeast of Key West and moving along the
 entire length of the Keys, killing 193 people, with 124 of those
 being overseas railroad workers in houseboats near Long Key and
 on a transport boat evacuating workers. At Sand Key, the minimum
 pressure was 29.25 inches of mercury, with a peak wind of 75 mph,
 and at Key West the minimum pressure was 29.30 inches of mercury,
 with a peak wind of 54 mph.
&&

.PRELIMINARY POINT TEMPS/POPS...
Key West  83  77  85  77 /  60  50  40  10
Marathon  83  77  85  77 /  70  60  40  10
&&

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...Small Craft Advisory until 5 PM EDT this afternoon for
     GMZ031>035-042>044-052>055-072>075.

     Gale Watch from this afternoon through late tonight for
     GMZ031>035-042>044-052>055-072>075.
&&

$$

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

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