Big Torch Key, Florida Weather Forecast Discussion

156
FXUS62 KKEY 180229
AFDKEY
Area Forecast Discussion
National Weather Service Key West FL
1029 PM EDT Wed Sep 17 2025
...New DISCUSSION, MARINE, AVIATION...
.DISCUSSION...
Issued at 1025 PM EDT Wed Sep 17 2025
Compared to earlier in the day, the late afternoon and evening has
been generally uneventful. KBYX radar has remained active through
the shift however. There was shield of rain with embedded
thunderstorms across the southwestern Straits of Florida for much
of the shift. However, the thunderstorms remained just on the
outside of the forecast area with only the steady rain reaching
into the southwest Straits. It looked like this band of light to
moderate rain might reach the Lower Keys but upon arrival it
entrained dry air which can be seen on the 00z evening sounding.
We go into more depth on this in the short term forecast section
below. Also, there have been persistent showers and isolated
thunderstorms across the eastern Straits of Florida for much of
the evening. Recently, a couple isolated showers developed across
the offshore Gulf waters north of the Lower Keys as well as in
Florida Bay. Temperatures along the Island Chain are in the lower
80s with dew points in the lower to mid 70s. Marine platforms
surrounding the Island Chain are observing northeast to east
breezes near 15 knots due to a tightening of the pressure gradient
of weak high pressure to the north of the Bahamas and weak low
pressure across the northwestern Caribbean south of Cuba.
.SHORT TERM FORECAST...
The 00z evening sounding continues to depict a post convective
environment. There is a stout dry air layer from the surface up to
around 700 mb. This can be seen on the radar imagery this evening
as the shield of rain over the southwestern Straits of Florida
looked like it was going to make at least to the Lower Keys but
upon arrival entrained this dry air. The PWAT value measured
though has continued to rise since the weekend now at 2.15
inches. This is at the 90th percentile for the date. In other
words, there is plenty of moisture in the air. Instability shows a
CAPE value measured around 1000 J/kg. While still unstable, it is
not close to how unstable we were this time last evening when we
had 2500 J/kg. Therefore, based on the latest radar trends, CAPE
not being as high, and the worst activity remaining south of the
region, decided to introduce timing into the forecast for
overnight with chances of rain and slight chance of thunder
through around midnight with showers becoming likely with a chance
of thunderstorms heading towards daybreak.
&&
.MARINE...
Issued at 1025 PM EDT Wed Sep 17 2025
Small Craft Should Exercise Caution (SCEC) is headlined for the
Straits of Florida for overnight. From synopsis, an unsettled
weather pattern is in place across southern Florida, and the
recent increase in showers and thunderstorms will remain in place
for the next couple of days. Breezes are expected to remain
moderate to fresh overnight with Small Craft Should Exercise
Caution headlined for the Straits of Florida. Breezes will slacken
by tomorrow, but showers and occasional thunderstorms will linger
across the area through the end of the week.
&&
.AVIATION...
(00Z TAFS)
Issued at 1025 PM EDT Wed Sep 17 2025
VFR conditions are expected to persist through the TAF package.
Latest radar imagery has most of the shower and thunderstorm
activity over the Straits of Florida. This is expected to continue
for the next few hours with more shower and thunderstorm
development expected overnight into the morning hours on Thursday.
As of now, the next best chance time for activity to make a
resurgence appears to be overnight with the threat continuing
through Thursday. Any showers and storms will be capable of
reducing VIS and CIGs to MVFR, potentially IFR, gusty winds, and
occasional to frequent lightning strikes. Near surface winds will
remain northeast to east between 5 to 12 knots with occasional
gusts to near 20 knots.
&&
.PRELIMINARY POINT TEMPS/POPS...
Key West  89  76  88  78 /  80  80  80  60
Marathon  88  78  87  78 /  80  80  80  60
&&
.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...None.
&&
$$
Public/Marine/Fire...MJV
Aviation/Nowcasts....MJV
Data Acquisition.....MC
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NWS KEY Office Area Forecast Discussion