Area Forecast Discussion
Issued by NWS Key West, FL

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628
FXUS62 KKEY 131438
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
1038 AM EDT Thu Aug 13 2026

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

.KEY MESSAGES...

- A Coastal Flood Statement remains in effect for the Lower and
  Middle Keys, with minor saltwater flooding possible, especially
  around the time of high tide late this morning and afternoon.

- Rain and thunder chances through tonight will generally be
  limited to any island cloud line formation or storms pushing off
  the South Florida Mainland.

- The best chances for measurable rainfall will be Friday through
  Saturday evening, before a swath of dry air progresses towards
  the Keys for late weekend and early next week.

&&

.DISCUSSION...
Issued at 1037 AM EDT Thu Aug 13 2026
CIMSS products continue to show split deep mean layer ridging in
place across the western North Atlantic, Florida, and the Gulf.
The split is located across the SE Bahamas with the center of one
ridge across the central North Gulf Coast and the other one to the
north northeast of the Lesser Antilles. Marine observation
platforms surrounding the Island Chain are recording east to
southeast breezes near 5 knots as a result. GOES 19 Total
Precipitable Water (TPW) shows PWAT values much higher this
morning when compared to 24 hours ago. Estimated values are
between 1.75 to 2 inches. Some remnant boundaries across the SE
Gulf have initiated with some convection this morning as picked up
by KBYX radar. This activity is slowly moving off to the west
southwest with occasionally some of the activity becoming a
thunderstorm. GOES 19 Visible satellite imagery shows an ample
popcorn nature to the cloud field across the SE Gulf in
association with the convection and mainly low level cumulus
clouds elsewhere. Temperatures along the Island Chain are in the
upper 80s to near 90 degrees and dew points are in the mid to
upper 70s.

.SHORT TERM FORECAST...
The 12z morning sounding paints a much different picture today
than it did yesterday. The sounding is more unstable along with a
deeper moisture profile through the entirety of the atmospheric
column. Instability is quite high with CAPE values above 2000
J/kg. The PWAT value measured is also much higher than yesterday
at 1.89 inches. This is very close to the mean and median for the
date. The wind profile is a little chaotic with southeast to south
winds in the lowest 2000 ft and east around 3000 ft with speeds
of 3 to 8 knots. Overall, a similar environment is in place across
the Keys today. The one difference is much more moisture is in
place today compared to yesterday. Therefore, an island cloud
remains possible this afternoon into this evening perhaps more
rigorous than the one yesterday. Also, convection is expected to
spill southwestward again this evening off the mainland due to the
northeasterly steering flow. Therefore, no changes expected to
the current ongoing forecast.

&&

.PREV DISCUSSION...
Issued at 400 AM EDT Thu Aug 13 2026
As hypothesized when writing this discussion last evening,
despite substantial dry air above 850 mb throughout the day today,
it is always humbling to remember it is mid-August in the Florida
Keys. Light winds supported broken island cloud line formation
across the Lower and Middle Keys, although the aforementioned dry
air largely stinted associated shower activity. Scattered strong
convection developed across the South Florida Mainland, then
propagated southwestward in the late evening hours towards the
Florida Keys marine zones, before later interacting with a
residual lurking ghost boundary north of the Lower and Middle
Keys. Since then, the isolated to scattered activity has waned,
leaving the entire CWA free of meteorological echo returns.
Outside of briefly rain- cooled locations between Big Pine and
Marathon, temperatures are generally in the lower to mid 80s at
this early morning hour for all land- based surface observation
locations.

For today, KBYX radar continues to detect residual ghost
boundaries lurking throughout the marine zones. Forecast soundings
indicate very little change to the synoptic setup, with weak mean
northeasterly steering flow likely supportive of additional cloud
line formation this afternoon. There is at least some convective
allowing model (CAM) support for convective development over South
Florida progressing southwestward tomorrow evening. Given the
aforementioned lurking boundaries and the convective evolution on
Wednesday (a persistence forecast), elected to nudge PoPs upward a
bit (around 20%) for both this afternoon and tonight.

Beyond today, high pressure will once again strengthen in the
North Atlantic over the next several days, supporting modestly
freshening easterly breezes. A tropical wave in the vicinity of
Puerto Rico will propagate westward towards the Straits of Florida
over the next several days, supplying associated boundary layer
moistening and cyclonic vorticity support for convection. A late
season undulation of Saharan dust will trail the wave. As these
two features interact, there will be an elevated chance for rain
and thunder, first as the wave approaches the Keys, then again as
the Saharan dust takes dominance over the Keys. Timing these
windows of elevated rain and thunder chances will be left to the
next several forecast cycles, lying somewhere between Friday
afternoon and Saturday evening.

Global deterministic and ensemble numerical weather prediction
guidance diverges a bit for late weekend through early next week.
Although the Saharan, dry environment looks to stay for quite some
time, a weak frontal boundary may stall somewhere to the north of
the Keys. For now, will yield to slightly below normal rain
chances, although this will be monitored, depending on the
stalling frontal evolution.

In terms of the tropics, although the National Hurricane Center is
monitoring two possible areas in the Main Development Region of
the Tropical Atlantic, neither system is expected to provide impacts
to the Keys at this time.

&&

.MARINE...
Issued at 1037 AM EDT Thu Aug 13 2026
A Coastal Flood Statement remains in effect for the Lower and
Middle Keys, with minor saltwater flooding possible around the
time of high tide late this morning through the early afternoon
hours. Boaters can expect less clearance under fixed bridges,
especially around the time of the high tide. From synopsis, a high
pressure system in the central North Atlantic will continue to
slide eastward and weaken this afternoon. Gentle east to southeast
breezes will slacken, becoming light and variable this afternoon
before becoming northeast to east this evening. As the high
restrengthens and builds westward, breezes will somewhat freshen
for Friday through the weekend. A weak frontal boundary will
approach the Florida Peninsula early next week, allowing breezes
to slacken once again, becoming light and variable at times.

&&

.AVIATION...
(15Z TAFS)
Issued at 1037 AM EDT Thu Aug 13 2026
VFR conditions are expected to persist at both EYW and MTH
terminals through the TAF period. Near surface winds will remain
mostly east to southeast through the period with perhaps another
period of northeast to east winds this evening. There remains the
possibility of another cloud line today which may cause showers
this afternoon near the terminals. Also, convection on the
mainland may spill southwestward again this evening after 14/00z.
Due to the uncertainty in timing and placement, VCSH was not
included at this time.

&&

.PRELIMINARY POINT TEMPS/POPS...
Key West  92  83  92  81 /  20  20  30  40
Marathon  90  83  90  82 /  20  20  30  40

&&

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

$$

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

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