National Weather Service

Area Forecast Discussion
Issued by NWS Key West, FL

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FXUS62 KKEY 230840
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
440 AM EDT Mon Sep 23 2024

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

.DISCUSSION...
-- Changed Discussion --Issued at 440 AM EDT Mon Sep 23 2024

Quiet conditions for late September prevail along the Florida Keys
on this early Monday morning, with radars detecting just isolated
showers over the Gulf waters north of the Middle Keys and the
distant Straits of Florida. Temps along the island chain are
mostly in the lower to mid 80s, but have radiated down to the mid
70s at the usual North Big Pine cool spot under mostly clear skies
and light winds. Surface analysis depicts weak high pressure over
the Eastern Seaboard, with a developing tropical low pressure area
over the northwestern Caribbean Sea. Aloft, an expansive mid/upper
level ridge extends eastward from South Texas across the Gulf of
Mexico and Florida peninsula. The 00Z Key West sounding sampled a
drier than normal airmass, with PW of 1.60 inches just above the
25th percentile for the date. Recent GOES-TPW satellite imagery
shows similar estimated PWs remaining in place around the Keys.

Today will see one last mainly dry day across the area, as
extensive dry air in the mid/upper levels thanks to the ridge
aloft continues to suppress most convection. Slightly stronger
easterly steering flow today as compared to the past few days
should be less favorable for island cloud line development, and
will also tend to shunt late afternoon/evening convection westward
from the southern mainland into the Gulf waters. Have continued
with slight chance (20 percent) PoPs for today, extending into
this evening. Otherwise, expect the warmest day of the upcoming
week, with high temps reaching the lower 90s. Dewpoints in the mid
70s should keep heat indices just below advisory criteria. Rain
chances should begin to ramp up late tonight and Tuesday as
gradually deepening moisture moves into our region on increasing
ESE flow.

The rest of the forecast depends almost entirely on the future
development and movement of the tropical low pressure area
currently over the NW Caribbean. The latest NHC outlook calls for
likely development of this system into a tropical cyclone within
the next couple of days, with the system then expected to move
northward across the eastern Gulf of Mexico with additional
development possible through the week. Considerable uncertainty
remains as to timing and exact track, as the system does not yet
have a well-defined circulation. As such, it is too early to nail
down specific impacts to the Keys. In general, we expect an
extended period of wet and windy weather beginning Tuesday night
and continuing all the way into Friday. We may see several inches
of rainfall during this time, and the expected strong SE flow
could also aggravate existing higher than normal tides. It is
especially important to not focus on the central track for this
system, as impacts will likely extend far to the east of the
center, given its origin from the Central American Gyre. Even
heading into the late week, when the system will probably be well
northwest of our area, model guidance suggests that we may be
stuck in the convergent moisture tail for quite some time, perhaps
right into the weekend. This would further extend the period of
above normal rain chances.

Residents and visitors in the Keys should continue to check back
for the latest forecast updates from the National Hurricane Center
and the National Weather Service office in Key West through the
upcoming week.-- End Changed Discussion --

.MARINE...
-- Changed Discussion --Issued at 440 AM EDT Mon Sep 23 2024

A Coastal Flood Statement remains in effect for all of the Keys
island chain, as above normal tides continue. Boaters can expect
less clearance under fixed bridges, especially during the hours
around high tide.

Late night observations show mostly E to SE breezes of 5 to 10
knots along the reef and at Long Key C-MAN, with seas at Satan
Shoal running around 1.4 feet. From the synopsis, gentle easterly
flow across the Keys coastal waters today will steadily increase
tonight and Tuesday, as high pressure builds along the Eastern
Seaboard, and a tropical low develops in the northwestern
Caribbean Sea. Heading through the middle and later part of the
week, the forecast will depend on the development and movement of
this low. At this time, we expect fresh to strong east to
southeast breezes to develop late Tuesday, with strong southeast
winds peaking Wednesday night into Thursday as the tropical system
moves northward across the eastern Gulf of Mexico. The strongest
winds and highest seas are expected over western sections of the
Keys waters. Mariners should continue to closely monitor the
latest forecast updates during the next few days.-- End Changed Discussion --

.AVIATION...
-- Changed Discussion --(06Z TAFS)
Issued at 440 AM EDT Mon Sep 23 2024

Both EYW and MTH will experience prevailing VFR conditions through
Monday evening. Very broad wind convergence south of the Lower
Keys will support short lived showers across nearshore waters, and
brief periods of VCSH are possible, but unlikely and thus left
out of the TAFs. Generally easterly near surface winds will
slowly increase to near 10 knots throughout the period.-- End Changed Discussion --

.CLIMATE...
-- Changed Discussion --
On this day in 1931, the daily record rainfall of 2.10" was recorded
in Key West. Precipitation records for Key West date back to 1871.-- End Changed Discussion --

.KEY WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --FL...None.
GM...None.-- End Changed Discussion --
&&

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

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