Grassy Key, Florida Weather Forecast Discussion

449
FXUS62 KKEY 221722
AFDKEY
Area Forecast Discussion
National Weather Service Key West FL
122 PM EDT Mon Sep 22 2025
...New AVIATION, PREV MARINE, DISCUSSION, AND FORECAST...
.AVIATION...
(18Z TAFS)
Issued at 114 PM EDT Mon Sep 22 2025
While VFR conditions will prevail across the terminals through 18z
Tuesday afternoon, additional scattered shower and thunderstorm is
expected by late this evening or in the overnight period.
Confidence in timing for this redevelopment is lower than normal
at this time, with an approximate period for which VCSH
commences included in the TAFs for now. This period will be
reevaluated through this evening, with adjustments to be expected.
Outside of any stronger storm, near- surface winds will remain
out of the east to southeast at 6 to 9 knots.
&&
.MARINE...
Issued at 1015 AM EDT Mon Sep 22 2025
There are currently no watches, warnings, or advisories in effect
across the Florida Keys coastal waters. From synopsis, as a
moisture surge pushes across the Florida Keys, rain and thunder
chances will be elevated for this afternoon through Tuesday. High
pressure over the Eastern Seaboard will sliding eastward will
support light to gentle east to southeast breezes. Mainly light
breezes, occasionally light to gentle will prevail for much of the
rest of the week, as weak high pressur114e remains across the
Florida Peninsula.
&&
.PREV DISCUSSION...
Issued at 1015 AM EDT Mon Sep 22 2025
Composite tropospheric vorticity and wind analysis places a number
of features interacting to dictate the sensible weather for the
Florida Keys at this late Monday morning hour. A stubborn upper-
level trough remains parked across the Gulf, with the base of the
trough located just north of the Yucatan Peninsula. Meanwhile, an
inverted low- and mid-level trough is currently overtop of the
western Bahamas slowly progressing westward. At the surface,
sprawling high pressure extends across the Eastern Seaboard and
much of the North Atlantic. The 12z morning sounding at KEY
sampled a conditionally unstable profile, limited inhibition, and
progressively veering low-level winds. Available Doppler radar is
currently highlighting a convective lull across the Florida Keys
and the adjacent coastal waters, but given the synoptic setup and
the sounding, fully expect convection to reinvigorate later this
afternoon and evening. Likely measurable rain and chance- level
thunder seems on par with this, although most convective- allowing
model (CAM) guidance delays onset until the overnight period. We
will monitor convective trends this afternoon, but no changes
proposed at this time.
&&
.FORECAST...
Issued at 430 AM EDT Mon Sep 22 2025
A broad upper trough across the Gulf will slowly lift to the
northeast through tonight. In conjunction with this, a weak
inverted trough is slowly propagating westward towards the Florida
Keys early this morning. In the lower to mid levels, there is also
a fair amount of moisture streaming into the area. GOES East
Total Precipitable Water (TPW) products shows mainly 1.9 to 2.1
inch PWAT across the area. However, lurking not too far away is
even moister air with PWATs generally of 2.2 to 2.3 inches.
Therefore, we have a supportive upper level environment, plenty
of moisture, and instability (00z evening sounding measuring CAPE
values near 3000 J/kg), we expect more widespread showers and
thunderstorms today and tonight. Due to this, 60% remains in the
forecast for these two periods.
As the upper level trough lifts northeastward, some weak ridging
builds into the region. However, some moisture will remain keeping
rain chances elevated for one more day on Tuesday at 50%.
Slightly drier air moves into the area for mid week through the
weekend resulting in 30% PoPs through the period. This is right
around average rain chances for this time of year. Otherwise,
typical summer weather is expected from Wednesday onward with
highs near 90 and lows near 80 with some lower 80s in areas.
&&
.PRELIMINARY POINT TEMPS/POPS...
Key West  88  79  89  81 /  60  60  40  30
Marathon  89  80  89  81 /  60  60  50  30
&&
.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...None.
&&
$$
Public/Marine/Fire...BT
Aviation/Nowcasts....BT
Data Acquisition.....AJP
Visit us on the web at weather.gov/key
Follow us on Facebook and Twitter at:
www.facebook.com/nwskeywest
www.twitter.com/nwskeywest

NWS KEY Office Area Forecast Discussion