Big Pine Key, Florida Weather Forecast Discussion

634
FXUS62 KKEY 131857
AFDKEY
Area Forecast Discussion
National Weather Service Key West FL
257 PM EDT Sat Sep 13 2025
...New AVIATION...
.AVIATION...
(18Z TAFS)
Issued at 255 PM EDT Sat Sep 13 2025
VFR conditions are expected at both EYW and MTH for the rest of
the day, but while rain chances have decreased showers still
cannot be fully ruled out at either terminal. If enough
convection develops on mainland Florida, outflow could spark
showers and storms near the island chain, especially near MTH,
later this evening. As there is low confidence in the exact timing
and location of this event no mention is in either TAF at this
time. Near surface winds will continue to be generally out of the
north at 5 to 10 knots.
&&
.PREVIOUS DISCUSSION...
Issued at 1147 AM EDT Sat Sep 13 2025
A relatively quiet morning continues on for the Florida Keys after
last night`s active period. Surprisingly, partly cloudy skies are
observed on GOES-19 visible imagery as cloud debris from last
night`s mesoscale convective system (MCS) shifts over the Bahamas
and out of our waters. Meanwhile, some high clouds are still
present due to persistent showers in the distant Straits of
Florida, but are quickly deteriorating. KBYX radar also detects
some showers percolating along boundaries extending through the
Deep Gulf waters and over across the Middle Keys, though lightning
has been more absent then not. As this boundary pushed over the
Upper and Middle Keys, gentle northeast breezes backed to the
north across our eastern offshore observation stations along the
Reef. A similar separation of temperature values is also seen on
land as observations on the Upper Keys are reading in at around 81
degrees with the rest of the island chain being a few degrees
higher. Dewpoints are still floating about the mid 70s.
Uncertainty prevails in the short term forecast period as a few
environmental features are presenting differently than originally
expected. The front that had been rooted over mainalnd Florida for
so long has sunk south over our waters towards Cuba taking away a
possible source of synoptic lift. Meanwhile, the upper level
trough axis is still nosed over the Yucatan Peninsula displacing
upper level support for convective development out towards the
Bahamas rather than encompassing our waters. The most surprising
feature is drier air descending along the west coast of Florida.
While this morning`s KKEY 12z sounding was not particularly dry,
a land shadow is present off of the southwest coast of mainalnd.
TBW`s 12z sounding is is quite dry this morning above the surface
with northerly winds advecting more dry air near the lower levels
and pushing it down the coastline. These factors plus the fact
that the overnight MCS arrived when it did, explains the lull in
activity we are currently observing. That being said, some
convection is still trying to bubble in the Gulf, particularly
along boundaries located outside of the path of the old MCS. Will
keep PoPs where they are with the high end of guidance as there
are certainly enough ingredients around for wet season to do its
thing before drier air fully seeps in.
&&
.FORECAST...
Issued at 430 AM EDT Sat Sep 13 2025
Confidence in the forecast beyond today remains quite low. While
the upper-level trough will slowly lift northeastward, global
ensemble numerical weather prediction (NWP) mean products suggest
the surface boundary will continue to flirt with the Keys through
the work week. As the surface high north of the boundary
strengthens and builds southward, the pressure gradient will
likely increase, supporting freshening easterly breezes. Where the
moisture gradient associated with the boundary ends up in
relation to the Keys will determine measurable rain chances.
Current NWP products suggest drier periods Monday night into
Tuesday, before a return to elevated rain and thunder chances for
Tuesday night and beyond. Temperatures will remain seasonably
warm, with highs in the upper 80s to near 90, and lows in the
upper 70s to near 80.
&&
.MARINE...
Issued at 1147 AM EDT Sat Sep 13 2025
No watches, warnings, or advisories are currently in effect for
the coastal waters of the Florida Keys. From synopsis, a weak
frontal boundary will remain in the vicinity of the Florida Keys
coastal waters over the next several days. Weak undulations of
this feature, interacting with high pressure to its immediate
north, will result in a low confidence forecast for winds and rain
chances. Gentle to moderate northeast to east breezes are
expected to build in by Tuesday or Wednesday, as the axis of the
high pressure finally is able to spread down closer to the Keys
marine zones.
&&
.PRELIMINARY POINT TEMPS/POPS...
Key West  78  89  79  90 /  50  40  40  40
Marathon  78  88  79  89 /  50  40  40  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