892
FXUS62 KKEY 200846
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
446 AM EDT Sun Sep 20 2026

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

.KEY MESSAGES...

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

- Heavy rainfall is expected at times. There is a marginal risk
  for excessive rainfall through Monday morning.

- 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 351 AM EDT Sun Sep 20 2026
GOES-19 satellite imagery shows broad cyclonic flow across the
entire state of Florida as an upper level low continues to remain
stalled in the eastern Gulf waters off the SWFL coast. This
feature has failed to make much westward progress as ridging aloft
near the Ark-La-Tex region remains in place so this disturbance
will continue to linger in the eastern Gulf waters for the
remainder of the weekend and into the start of the new week.
Despite the close proximity of this feature, the core of cold air
aloft has remained to the north of our area so far this weekend
and the 20/00Z KEY RAOB sampled a 500 mb temperature of -5.7 C,
which was considerably warmer than the sounding from Saturday
morning which had a value of -8.3 C, near the 10th percentile for
this time of the year. Thus, this warming trend aloft has likely
played a significant role in why convective development has been
more suppressed than what the official forecast and model guidance
had suggested so far this weekend. That said, will continue to
maintain elevated rain chances for the remainder of the weekend as
the upper level low to the north continues to still favor
increased forcing for ascent across the region with divergence
aloft and an increase in vorticity advection. Since this feature
remains in an environment of weak steering, it may be able to
drift just far enough southward today to possibly allow mid level
temps to cool a touch further once again and bring a slightly more
favorable thermodynamic environment today with better mid-level
lapse rates compared to what was observed yesterday. Additionally,
the low level flow will become more southerly today so this
should bring a slight uptick in moisture quality with PWATs in
excess of 2 inches area-wide, though the southerly flow will also
of course be more susceptible to Cuban shadow influence.
Regardless, there should be enough ingredients in place to support
scattered to occasional numerous showers and thunderstorms across
the Florida Keys and surrounding coastal waters today, which
could also be enhanced further if a cloud line is able to take
advantage of a light/VRB wind flow developing in the late
afternoon hours. While the cloud line scenario remains to be seen,
activity should have no issues developing late evening and
overnight as there should be plenty of mesoscale boundaries during
the overnight hours to provide additional initiation sources.

The upper level low is forecast to open into a trough late Monday
and into Tuesday as it becomes absorbed in a mid-latitude trough
into mid week. Lingering moisture in the wake of this feature
should still support elevated rain chances on Monday with PoPs
peaking from 50% to 70%. As the weakening upper low lifts off of
Northeast FL on Tuesday, it will aid it in the development of
coastal low off in Southwest Atlantic with this system expected to
lift to the north-northeast through mid to late week, deepening as
it does so. As this occurs, a frontal boundary associated with
this system will drop southward across the central Florida
peninsula mid week and potentially push through south Florida
by the end of the week. Whether or not this frontal boundary can
push all the way through south Florida and the Keys remains in
question at the moment, but a deepening upper level trough across
the eastern CONUS may provide enough push to allow the boundary to
sweep through. If this frontal passage occurs, the air mass
change in the wake of the boundary this early in the season may
fall short of bringing a significant noticeable change in
temperatures with a decrease in dewpoints and humidity values
being the more likely outcome. In addition to this frontal
boundary, there will also be a surge of tropical moisture being
funneled northward from the Caribbean potentially associated with
an inverted trough feature that may move across the Yucatan
Channel. While amplifying ridging across east Texas in the middle
of the week and the aforementioned frontal boundary pushing
southward across the peninsula would suggest that most of the
moisture associated with this increase in tropical moisture should
get directed to the west of the Florida Keys, there should be
enough increase in moisture to keep rain chances elevated through
the middle of the week before moisture levels decrease towards the
end of the week as the frontal boundary drags a drier air mass
into the region.

&&

.MARINE...
Issued at 351 AM EDT Sun Sep 20 2026
Light to gentle mainly southerly breezes will be in place through
the remainder of the weekend, though a period of variable winds
are expected during the late afternoon and evening hours on
Sunday. In addition, a wet weather pattern will continue to
persist across the Florida Keys coastal waters into the new week
as an upper-level low lingers in the eastern Gulf waters. As a
result, scattered to 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 by Tuesday,
but lingering moisture is likely to persist through at least the
middle of the week so rain chances will continue to remain
elevated. Winds will generally remain light to gentle into the new
week but brief periods of moderate winds may occur in the evening
hours with winds remaining mostly out of the south to southeast.

&&

.AVIATION...
(06Z TAFS)
Issued at 351 AM EDT Sun Sep 20 2026
Scattered SHRA/TSRA may occur as times throughout the period a
slow moving disturbance lingers to the north of the Florida Keys.
If any of this activity directly impacts either of the Island
Chain terminals, brief flight restrictions of MVFR/IFR will be
possible, especially during periods of heavier precipitation.
Outside of any the shower and thunderstorm activity, VFR
conditions will prevail with mostly light southerly winds around 5
kts today, potentially becoming light/VRB briefly this evening
before increasing to 5-10 knots overnight out of the south.

&&

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

$$

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

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