Key Largo, Florida Weather Forecast Discussion

444
FXUS62 KKEY 170233
AFDKEY
Area Forecast Discussion
National Weather Service Key West FL
1033 PM EDT Tue Sep 16 2025
...New DISCUSSION, MARINE, AVIATION...
.DISCUSSION...
Issued at 1033 PM EDT Tue Sep 16 2025
The weather pattern is about to change. A frontal boundary that
has been festering to the south of the Florida Keys is beginning
its movement back to the north tonight. Most of the evening has
remained quiet with that just now starting to change. KBYX radar
is beginning to pick up on showers developing across the nearshore
waters around the Island Chain with the more robust activity
across the far southern distant Straits. Temperatures along the
Island Chain are in the mid 80s with dew points in the mid to
upper 70s. Marine platforms surrounding the Island Chain are
observing northeast to east breezes of 5 to 10 knots as we remain
to the north of the frontal boundary.
.SHORT TERM FORECAST...
The 00z evening sounding is quite unstable tonight. There are
distinct moist layer with the first one being between 925 to 900
mb and the second one between 475 to 425 mb with a lobe of dry
air in between these layers. The CAPE values measured was 2522
J/kg which is quite unstable and plenty of fuel for thunderstorms.
Also, the PWAT value measured was 1.96 inches which is indicative
of a very moist atmosphere. This number has been increasing ever
since the weekend and is also close to the 75th percentile for the
date. Then we also have the trigger being the frontal boundary
lifting back to the north. Therefore, we have all the ingredients
needed for quite the active overnight continuing through at least
Friday. Therefore, no changes to the ongoing forecast.
&&
.MARINE...
Issued at 1033 PM EDT Tue Sep 16 2025
There are currently no watches, warnings, or advisories in effect
across the Florida Keys coastal waters. From synopsis, a very
stubborn, weak frontal boundary in the vicinity of the Florida
Keys will drag closer to southern Florida over the next few days.
The resulting increase in moisture will lead to showers and
thunderstorms with the most activity expected some time over
Wednesday and Thursday. Freshening northeasterly to easterly
breezes will peak Wednesday night, and Small Craft Should Exercise
Caution headlines may be needed, especially across the waters to
the south of the island chain. Breezes should slacken and weather
conditions should dry out to some degree as we head into the
weekend.
&&
.AVIATION...
(00Z TAFS)
Issued at 1033 PM EDT Tue Sep 16 2025
VFR conditions are expected to prevail for the next few to
several hours at both terminals. A much wetter pattern is about to
begin across the area with KBYX radar showing widespread shower
and thunderstorm activity across western Cuba and just outside of
the forecast area. The timing for any showers and thunderstorms
remains uncertain but current thinking is the activity holds of
till around 17/12z Wednesday morning. However, if any showers and
thunderstorms can develop ahead of the ongoing storms, the timing
may be moved up a few hours. Rounds of showers and thunderstorms
will continue for the next few days with the timing and placement
for any individual round uncertain. Any showers and thunderstorms
will be capable of producing MVFR CIGs and VIS with the potential
for even IFR CIGs and VIS, gusty winds, and occasional to frequent
lightning.
&&
.PRELIMINARY POINT TEMPS/POPS...
Key West  89  79  89  77 /  30  60  70  80
Marathon  89  79  88  78 /  30  60  70  70
&&
.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