846
FXUS62 KKEY 181725
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
125 PM EDT Fri Sep 18 2026

...New AVIATION...

.KEY MESSAGES...

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

- Heavy rainfall is expected at times. There is a marginal risk
  for excessive rainfall through the middle of 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.

&&

.AVIATION...
(18Z TAFS)
Issued at 115 PM EDT Fri Sep 18 2026
After a lull in activity, scattered showers and thunderstorms
will develop after 18z, continuing into the evening in the vicinity of
the terminals. Activity will be slow moving, resulting in bouts of
sub-VFR ceilings and visibilities. Another lull is expected for
much of the overnight hours, before regeneration of activity
occurs thereafter. Have included general VCSH for the latter half
of the forecast period, with low confidence in that forecast. VFR
conditions are expected outside of any shower or thunderstorm
activity with surface winds around 5-8 kts today out of the
northeast to east.

&&

.PREV DISCUSSION...
Issued at 301 AM EDT Fri Sep 18 2026
The synoptic picture reveals an anomalously strong upper level
ridge (600 dam) that remains centered around the lower MS Valley
and an upper level low is positioned in the Atlantic waters off
the Cape Canaveral area. Throughout the day, this feature will
retrograde westward as it tracks across the central Florida
peninsula before eventually shifting into the Gulf over the
upcoming weekend. Meanwhile, surface high pressure off the coast
of New England has an associated ridge axis extending
southwestward into the Southeast US, which is placing the Florida
Keys in an easterly low-level flow pattern. However, while the
flow has been mainly easterly throughout the entire atmospheric
column in recent days, there will be a noticeable change in the
mid to upper level wind pattern today as the cyclonic flow
influence associated with the aforementioned upper level low
becomes more apparent across the region with winds aloft becoming
more southwesterly as the upper low tracks by to our north. The
biggest change that will result from these opposing wind vectors
at different levels is that storm motions will likely be more
slow-moving and erratic than the westerly storm motions observed
in recent days, which enhances the potential for heavier rainfall
and localized flooding issues, particularly in locations that
receive heavier downpours for extended durations. As a result of
these concerns, WPC has placed all of the Florida Keys in a
Marginal risk of excessive rainfall for the next several days
given that this upper level low will be the main feature that will
influence our local weather pattern throughout the weekend and
into next week. This also means that rain chances each day will be
above climatological normal values, pretty much peaking in the
50-60% range through early next week. Regarding severe weather
potential, the core of the cooler mid level temperatures (-9C to
-10C at 500 mb) is forecast to stay just north of our area in
central FL but 500 mb temps may still fall to around -7C/-8C
across the Keys, which is still only between the 10th and 25th
percentile for mid September so this should favor some enhancement
to mid-level lapse rates at times and the development of stronger
cores aloft. Should this materialize, stronger wind gusts can`t
be ruled out if some of this activity can take advantage of the
increase in buoyancy despite the background shear values being on
the weaker side, though deep-layer shear values will increase a
touch by later in the weekend and into next week (sfc-6km near 20
kts) as the upper low meanders in the eastern Gulf. Overall, an
unsettled weather pattern is anticipated to end the week and
throughout the weekend with persistent forcing for ascent
remaining in place across the region, helping to maintain elevated
rain chances, localized flooding concerns, and occasional strong
wind gusts as daily scattered to occasional numerous showers and
storms are forecast to blossom across the Keys each day.

As the new week arrives, some question remains as to when this
upper level low will depart the region as the GFS maintains the
upper low in the eastern Gulf into Tuesday before eventually
lifting if northward into mid week but the ECMWF opens it into a
trough earlier in the week. Regardless of either scenario, deep
moisture is generally expected to remain across the Florida Keys
well into next week as southerly flow lingers in the wake of the
departing upper low. As we approach the end of the forecast period
next week in the mid to late week time frame, forecast models
show ridging aloft building across the central and southern Plains
with an upper trough/low around the Great Lakes region, likely
driving a frontal boundary gradually towards the Southeast US by
late week. Meanwhile, attention may also need to be focused to the
south of the Florida Keys with some potential for a surge of
tropical moisture approaching from the Caribbean. This moisture
surge appears to be related to the Central American Gyre (CAG) and
would align with a climatologically favored time of the year as
these features typically become more established in early Fall.
That said, the synoptic details are highly uncertain still but
there is some ensemble support with this moisture surge at this
time with both the GEFS and EPS showing about a 10%-20% chance of
PWATs in excess of 2.5 inches by the end of next week slowly
approaching the Florida Keys. As a result, will maintain a
consensus blend of models approach to PoPs to account for the
uncertainty regarding this pattern, which still keeps PoPs in the
high chance to likely range through the end of the forecast
period.

&&

.MARINE...
Issued at 1100 AM EDT Fri Sep 18 2026
Scattered showers and thunderstorms will grow in coverage and
intensity through the afternoon and evening hours. Any stronger
thunderstorm will be capable of producing gusty winds, as well as
suddenly building and confused seas.

From synopsis, high pressure in the North Atlantic will weaken
today, allowing winds to slacken across the Florida Keys coastal
waters. Light to gentle breezes will continue through the weekend.
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 Florida
Peninsula and eventually slides into the Gulf this 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 light to gentle. 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.

&&

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

$$

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

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