050
FXUS62 KKEY 221922
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
322 PM EDT Tue Sep 22 2026

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

.KEY MESSAGES...

- There is a marginal risk for excessive rainfall through Thursday
  morning as topical moisture spreads into the area over the next
  several days.

- Drier air associated with a cold front will arrive late week and
  into the weekend and will bring a lower risk of excessive
  rainfall, though some rain chances will linger.

- Increasing northeasterly swell in the wake of the cold front
  will allow seas to build by the end of the week and into the
  weekend, especially in the Straits of Florida.

&&

.MARINE...
Issued at 314 PM EDT Tue Sep 22 2026

Convection to afternoon is mostly limited to the Southeast Gulf
and far western waters with lesser coverage elsewhere. This lull
in the activity will be brief and expecting a renewed surge in
showers and thunderstorms this evening and overnight as deep
tropical moisture continues to push northward from the western
Caribbean. Outside of any passing convection, breezes will
generally be light to gentle with the exception of the Straits of
Florida, which will see gentle to moderate breezes. Breezes
overall will slacken going into the later half of the week in
advance of an approaching frontal boundary. Breezes may go light
and variable, especially over the waters north of the island chain
on Thursday. Thereafter, expecting freshening northerly breezes
behind a frontal passage Friday.

&&

.AVIATION...
(18Z TAFS)
Issued at 314 PM EDT Tue Sep 22 2026

We have entered a brief lull in convection, however, low
confidence as to how long this break will last. Therefore, have
opted to keep mentions of VCSH at this time. As we go into the
evening and overnight, a renewed surge in activity is expected as
deep tropical moisture continues to surge north out of the
Caribbean. Outside of convection, expect near-surface winds to
generally be 10 knots or less.

&&

.PREV DISCUSSION...
Issued at 409 AM EDT Tue Sep 22 2026

The upper level low that we have been tracking the past several
days has now opened into a trough as it lifts away from the region
off the northeast coast of Florida throughout the day. Remnant
energy associated with this departing disturbance will aid in the
development of a coastal low that will track in a general
northeast direction through the end of the week, deepening as it
gains latitude. A cold front attached to this system will push
southward into central Florida by Thursday and south Florida into
Friday as the low pressure system becomes increasing occluded and
retrogrades westward towards coastal New England by the end of the
week. Meanwhile, before this frontal boundary approaches our
area, we have a wet and stormy weather pattern on tap across the
Florida Keys over the next several days. 250 mb analysis is
showing a positively tilted trough extending into the Yucatan
Peninsula left in the wake of the departing aforementioned
disturbance. To the east of this feature, a deep feed of tropical
moisture with its source regions in the southwest Caribbean is
directed northeastward across Cuba, The Bahamas, and the Florida
Keys with PWATs possibly peaking as high as 2.5 inches either
later today or Wednesday. The increasing moisture advection and
PVA throughout the day supports rounds of scattered to numerous
showers and thunderstorms that will generally drift in a northward
direction across the region. Despite these favorable ingredients
to support well above normal PoPs today (60-80%), the southerly
steering flow in place does add some uncertainty to the convective
evolution as a Cuban shadow influence could ultimately bring a
decrease in overall coverage at times. Current thinking is that
forcing for ascent and anomalous moisture should ultimately win
the battle so our forecast reflects these likely/categorical PoPs
but certainly something to mention.

The heavy rainfall threat continues on Wednesday as an upper trough
axis sharpens across the eastern US, which will help to maintain a
tropical moisture connection. If PWATs are able to reach 2.5 inches,
this would be at daily maximum values for this time of the year but
even if it is slightly lower, values should still be at or above the
90th percentile of 2.16 inches. Steering flow on Wednesday might
also be able to have a slightly more westerly component and this may
be just enough to limit the drying influence from Cuba.
Additionally, forecast soundings show near saturated atmospheric
columns with the classic tall and skinny CAPE appearance so this
activity should be very sufficient rain producers with heavy
rainfall rates and quick accumulations. Thus, PoPs will continue
to remain well above normal throughout this time with localized
hydro impacts a possibility, particularly during high tide cycles
where drainage capacity is less. Overall, QPF amounts through
Wednesday night could be around 1.5-3 inches across the Florida
Keys, which aligns with HREF 50th percentile values. However,
should this event exceed expectations, values of 4-6 inches with
locally higher totals can`t be ruled out, which is shown in
several 90th percentile solutions. As a result, WPC highlights all
of the Keys for a Marginal risk of excessive rainfall through
Thursday morning.

Rain chances will drop a bit closer to climatological values
later in the week as aforementioned frontal boundary makes
southward progress across the Florida peninsula. Drier air aloft
spreads southward in the wake of this frontal boundary on an
exceptionally deep northerly flow across the entire eastern CONUS
on the backside of the nor`easter in the north Atlantic. However,
some PoPs may still linger late week and into the weekend as the
frontal boundary is expected to stall just north of Cuba in the
Straits so the deeper moisture may not be able to completely scour
out. Regardless, this frontal passage will certainly still be
noticeable despite a much less impressive air mass change
compared to what many areas further north will experience.
Dewpoints are still projected to drop into the low to mid 70s and
coupled with highs in the mid/upper 80s, this will be noticeable
after the typical prolonged duration of extreme humidity
experienced during Florida summers. However, it is still late
September and long range guidance suggests that the slight
decrease in humidity levels will be short-lived as return flow
setting up early next week allows moisture values to recover and
rain chances continuing to persist through the remainder of the
forecast period.



&&

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

$$

Public/Marine/Fire...LIW
Aviation/Nowcasts....LIW
Data Acquisition.....LIW

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