Big Pine Key, Florida Weather Forecast Discussion

590
FXUS62 KKEY 121940
AFDKEY
Area Forecast Discussion
National Weather Service Key West FL
340 PM EDT Fri Sep 12 2025
...New AVIATION...
.AVIATION...
(18Z TAFS)
Issued at 338 PM EDT Fri Sep 12 2025
VFR conditions will prevail at both EYW and MTH for the next few
hours, but another round of convection is likely this evening.
Outflow boundaries from Mainland Florida and Cuban convection
will allow for more showers and thunderstorms to form near the
island chain after this lull. VCSH is included as a rough
estimate to when precipitation returns to near either terminal.
Outside of convection, near surface winds will be generally light
and variable, becoming north to northeast.
&&
.PREVIOUS DISCUSSION...
Issued at 1145 AM EDT Fri Sep 12 2025
A moist and unstable environment is present across the Florida
Keys this morning with ongoing and developing showers and
thunderstorms. Before sunrise, KBYX detected a growing cluster of
showers and embedded thunderstorms in the Deep Gulf waters. A
nebulous flow kept the complex relatively contained to the area
for a few hours, but it eventually scrapped over the western edge
of the Lower Keys bringing gusty winds and lightning strikes.
Usually that would be it for the morning activity as this cluster
diminishes, but more convection is bubbling up both along the
outflow boundaries in the Straits of Florida and back in the Deep
Gulf waters. Needless to say, the atmosphere is quite energized at
the moment with precipitation forming despite light generally
northerly breezes (occasionally variable) across our Reef
observation stations outside of convection. Extra cloud cover
aloft has temperatures a touch cooler than yesterday at this time
as they report back in the mid 80s.
This morning`s active mode looks to be a harbinger of weather to
come in the short term forecast. Our 12z KKEY balloon sounding
observed yet another PW above the 90th percentile along with a
respectable ML CAPE value ~1750 J/kg. CIMSS MIMIC PW shows a sharp
gradient of values across central Florida notating the approximate
location of a stalled frontal boundary. To its south, values
greater than 2 inches are plentiful including across our area.
Meanwhile, upper level troughing is meandering east through the
Gulf slotting South Florida into an area favorable for convective
development. Thus we expect repeat of storms on South Florida
ejecting boundaries into our waters to spark another round of
storms later today. Then tomorrow, we look to repeat the process
over with nocturnal precipitation in the morning hours and likely
more induced from mainland outflow boundaries. The only limiting
factor is the lighter windfield found south of the front, although
this morning has already proved that does not seem to be much of
an issue. Will continue to hold 70 PoPs over the next few periods
with no changes to the forecast required at this time.
&&
.FORECAST...
Issued at 430 AM EDT Fri Sep 12 2025
Rain chances are expected to taper off through the back half of
the weekend, remaining slightly above normal. This will be due to
the trough being positioned to our south and hopefully some drier
air moving in through the mid and upper levels. Winds will
generally remain light but tend northeasterly due to surface
ridging to the north and the surface trough positioned across Cuba
and Bahamas.
Uncertainty continues to remain high through the upcoming week.
Guidance consistency remains quite low from run to run and model
to model regarding the possible return of the surface trough and
amplification of troughs/lows along this trough. A lot of this
will hinge on how the amplified, but quite complicated, trough
aloft behaves. Give these uncertainties and the likelihood that
deep layered moisture will remain high, will maintain mid to high
chance PoPs through the mid and long range. Surface winds have a
shot at firming up modestly out of the northeast to east as the
surface ridge over the eastern United States is expected to
finally reach southwards into the Keys.
&&
.MARINE...
Issued at 1145 AM EDT Fri Sep 12 2025
No watches, warnings, or advisories are currently in effect for
the coastal waters of the Florida Keys. From synopsis, a weak
surface trough strung across South Florida and the Keys will shift
southwards into the Straits over the next couple of days as high
pressure expands southward out of the southeastern United States.
The wet pattern will continue with rain chances likely trending
higher due to the migrating trough. Confidence is very low with
respect to the wind forecast. The trough is expected to stall not
too far off to the south and the fresher breezes associated with
the ridge further north should remain just out of our area through
the weekend. As a result, winds in the near term will be light,
often variable. However, showers and thunderstorms will deliver
localized higher winds and seas. Gentle to moderate northeast to
easterly breezes are expected to build in as the high finally is
able to spread down into our area. With that said, uncertainty
remains considerable.
&&
.PRELIMINARY POINT TEMPS/POPS...
Key West  77  89  78  89 /  60  70  60  40
Marathon  77  87  78  88 /  70  70  60  40
&&
.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...None.
&&
$$
Public/Marine/Fire...JAM
Aviation/Nowcasts....JAM
Data Acquisition.....JAM
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NWS KEY Office Area Forecast Discussion