Big Pine Key, Florida Weather Forecast Discussion

523
FXUS62 KKEY 210831
AFDKEY
Area Forecast Discussion
National Weather Service Key West FL
431 AM EDT Sun Sep 21 2025
...New DISCUSSION, MARINE, AVIATION...
.DISCUSSION...
Issued at 430 AM EDT Sun Sep 21 2025
It has been a generally quiet night across the Florida Keys. KBYX
radar detected some showers with an occasional thunderstorm
across the offshore Gulf waters earlier in the night. These
showers and storms were riding along what appeared to be outflow
boundary which moved off the South Florida mainland. This boundary
propagated all the way across the Gulf waters of the Keys and is
now outside the coverage area to the west. Most of the activity
with this boundary has dissipated. Temperatures along the Island
Chain are in the lower 80s with dew points in the upper 70s. A
strong high pressure is dominating much of the Eastern Seaboard
this morning combined with lower pressure in the Caribbean. Due to
this, marine platforms around the Keys are observing northeast to
east breezes of 10 to 15 knots.
.FORECAST...
The forecast going forward for the next few periods is
interesting. Weak troughing currently remains across much of the
Gulf with a ridge over the Atlantic. The western periphery of
this ridge remains just outside of the Florida Keys forecast
area. GOES Total Precipitable Water (TPW) products as well as
CIMSS Mimic Total Precipitable Water shows an area of increased
moisture festering near Andros Island. In addition, model guidance
is showing ridging building into west Texas which in turn will
act to sharpen the trough across the Gulf making it deepen. Some
upper level vorticity lobes rounding the western periphery of the
ridge in the Atlantic will merge with other vorticity lobes
migrating southeastward across the Gulf as the trough digs
southward. Therefore, increasing moisture across the area combined
with improving upper level support for convection, and
instability will lend to another active period to start the new
week. The rain chances for today remain unchanged at 30%. However,
starting tonight as the trough deepens and the vorticity lobes
start to move into the area, we expect more widespread shower and
thunderstorms to develop. As a result, PoPs were raised from 40%
--> 50% for tonight, Monday, and Monday night.
Tuesday through Wednesday, the trough remains but is weaker when
compared to tonight through Monday night. Also, some ridging
starts to build back into the Keys during this time with most of
the upper level energy remaining just north of the Keys before
potentially being pushed back south Wednesday or Wednesday night
as the region begins to feel the effects of the next trough diving
southeastward across the Southeast U.S. Therefore, PoPs come down
to 40% for this period, however, any subtle shift in these
features and the rain chances may change.
For the extended, model guidance is showing a fairly significant
trough moving southeastward towards the Gulf Coast. This trough
will act to push a region of drier air across the Gulf
southeastward towards the Keys. Right now, PoPs are at 30% but
this may very well change in subsequent updates to a drier
forecast. Outside of the rain chances, expect typical daytime
highs in the upper 80s and overnight lows near 80.
&&
.MARINE...
Issued at 430 AM EDT Sun Sep 21 2025
There are currently no watches, warnings, or advisories in effect
across the Florida Keys coastal waters. From synopsis, high
pressure over the Eastern Seaboard will lead to gentle to moderate
northeast to east breezes today. As we head into the new work
week, this high will shift farther out into the North Atlantic and
slowly weaken. As a result, northeast to east breezes shift to
east to southeast tonight while slackening to light to gentle
breezes. Mainly light breezes, occasionally light to gentle will
prevail for much of the week as weak high pressure remains across
much of Florida.
&&
.AVIATION...
(06Z TAFS)
Issued at 430 AM EDT Sun Sep 21 2025
VFR conditions will prevail at both EYW and MTH today. While a
stray shower or two cannot be ruled out, low confidence in exact
timing and location will leave mention out of either TAF for now.
Near surface winds will be out of the northeast to east at 5 to 10
knots.
&&
.CLIMATE...
On this day in Keys Weather History in 1948, a Hurricane
intensified as it moved north northeast off of Cuba, crossing Boca
Chica Key as category 3 storm. At Boca Chica the peak wind was
122 mph before the anemometer blew away, with an estimated peak
wind of 140 mph.
&&
.PRELIMINARY POINT TEMPS/POPS...
Key West  88  80  88  79 /  30  60  50  50
Marathon  89  79  89  79 /  30  50  50  50
&&
.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...None.
&&
$$
Public/Marine/Fire...MJV
Aviation/Nowcasts....JAM
Data Acquisition.....JAM
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NWS KEY Office Area Forecast Discussion