241
FXUS62 KKEY 190818
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
418 AM EDT Sat Sep 19 2026

...New DISCUSSION, MARINE, AVIATION...

.KEY MESSAGES...

- Well above normal rain chances (around 60-70%) will persist
  across the Florida Keys through the weekend and into early next
  week.

- Heavy rainfall is expected at times. There is a marginal risk
  for excessive rainfall through early next week.

- While breezes will be light to gentle (5 to 10 mph) throughout
  the weekend, gusty winds and locally hazardous seas are
  expected in the vicinity of thunderstorms.

&&

.DISCUSSION...
Issued at 306 AM EDT Sat Sep 19 2026
Broad cyclonic flow aloft is essentially in place across the entire
state of Florida as the well-advertised upper level low continues to
gradually retrograde across the central FL peninsula. Meanwhile, mid
to upper level ridging is in place across the Ark-La-Tex region and
this feature will prevent the upper low from making meaningful
westward progress in the coming days as the upper low is expected to
emerge into the eastern Gulf waters by tonight and linger in this
region into early next week. The influence of this feature across
the Florida Keys is evident in the latest 19/00Z KEY RAOB as winds
are generally from the WSW from about 650 mb and higher with a
mainly easterly wind profile below this layer into the low levels.
In addition, the 500 mb temperature sampled from this sounding was
-7.4C, which places this value within the 25th percentile per SPC
sounding climatology. While these mid level temperatures are
impressive for mid September, the core of the cold air aloft (around
-10C) will remain north of our region closer to the center of the
upper low but we are certainly close enough to still expect
enhancements to mid-level lapse rates at times. Regarding the
evolution of convection today, there are a variety of messy
solutions on the suite of CAM guidance as one would expect in an
environment of deep moisture with favorable synoptic ascent aided by
the presence of the upper low and enhanced divergence aloft. The
main limiting factors appear to be more on the thermodynamic side
with instability values not expected to be too impressive with
models showing MLCAPE values in the 500-1000 J/kg range, despite the
cooler mid level temperatures. Additionally, a dry slot circulating
around the upper low may try to punch into the region from the west
later today. Thus, there may be a bit of lull in convection by the
evening hours, especially if the atmosphere becomes very worked over
before the arrival of drier air. Regardless, if a lull in activity
does occur this evening, it should be short-lived as there will be
plenty of lingering boundaries around to allow for convection to
remain a concern going into the overnight hours. Locally heavy rain
and isolated strong wind gusts will remain the primary hazards with
any of the more robust activity that is able to materialize.

The upper low should generally stall somewhere off the coast of
the Tampa Bay area later in the weekend and place the Florida
Keys on the eastern side of the circulation. This should favor a
more deeper southerly wind profile and combined with better
positioning for vorticity advection, additional rounds of
convection will continue to be closely monitored. Heavy rainfall
and localized flooding will remain the main concern even as storm
motions should pick up somewhat later in the weekend. As a result,
WPC maintains a Marginal risk of excessive rainfall throughout the
weekend and into early next week across the Florida Keys with PoPs
remaining in the high chance to likely range throughout this time..
By Tuesday, models show the upper low will finally be opening
into a trough and becoming absorbed by a mid latitude trough
through mid week, though there are some signals that the remnants
of this feature could aid in the development of a coastal
trough/low off the Southeast US coast before this system lifts
northward later in the week. While model solutions differ in the
positioning and strength of this system, it may be able to send a
cold front southward into central FL and possibly south FL by mid
to late week. Meanwhile, as this occurs, a surge of tropical
moisture from the Caribbean is forecast to potentially push into
the the region, which appears to be related to the Central
American Gyre (CAG). While the specific forecast details remain
poor at this time, there continues to be some ensemble support
with about a 10-20% chance of PWATs greater than 2.5 inches
reaching the Florida Keys. However, with the upper level pattern
across the southern US featuring ridging in place across TX/LA,
this may be enough to steer the deeper moisture feed to the west
of our region but uncertainty still remains high at this time so
trends will continue to be monitored closely.

&&

.MARINE...
Issued at 306 AM EDT Sat Sep 19 2026
Light to gentle breezes will continue through the weekend with
winds mostly out of the east to start the weekend and gradually
shifting to the south to southeast into Sunday. In addition, an
increasingly wet weather pattern will develop across the Florida
Keys coastal waters through early next week, as an upper-level low
retrogrades westward across the central Florida Peninsula and
eventually slides into the eastern Gulf waters later in the
weekend. As a result, scattered to occasional numerous showers and
thunderstorms will be a daily occurence, with gusty winds,
lightning strikes, blinding downpours, and locally hazardous seas
being the main hazards mariners could encounter in the vicinity of
this activity. The upper-level low is forecast to move out of the
area early next week, with winds becoming more southerly and
breezes remaining mainly light to gentle, though occasional
periods of moderate breezes could occur at times. Rain chances
will also continue to remain elevated into next week, as deep
moisture lingers across the Florida Keys coastal waters in the
wake of the departing weather disturbance.

&&

.AVIATION...
(06Z TAFS)
Issued at 306 AM EDT Sat Sep 19 2026
Scattered SHRA/TSRA could move across portions of the Island Chain
at any time throughout the forecast period as a slow moving
disturbances passes by the north. If this activity impacts either
of the Island Chain terminals directly, brief MVFR/IFR
restrictions may occur, especially during pockets of heavier
rainfall. Otherwise, VFR conditions will mostly prevail outside of
any thunderstorm activity with surface winds out of the E today
and gradually shifting to the south tonight into Sunday.

&&

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...None.
&&

$$

Public/Marine/Fire...RG
Aviation/Nowcasts....RG
Data Acquisition.....DP

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