Key West, Florida Weather Forecast Discussion

942
FXUS62 KKEY 280818
AFDKEY
Area Forecast Discussion
National Weather Service Key West FL
418 AM EDT Sun Sep 28 2025
...New DISCUSSION, MARINE, AVIATION...
.DISCUSSION...
Issued at 421 AM EDT Sun Sep 28 2025
Weather across the Florida Keys will be defined by the nearby
Tropical Depression Nine, which was located just south of the
Bahamas as of 2 AM. TD Nine developed a bit more quickly than
expected yesterday, so winds across the Florida Keys are
freshening earlier than forecast. Breezes across the reef already
freshened to moderate northerlies before sunrise. KBYX and KAMX
radar returns show shallow showers pulsing over the easternmost
Florida Straits. Dew points remain in the mid 70s. A 06Z sounding
released from KKEY observed over 2 inches of precipitable water.
Ordinarily, the forecast would focus on how conditions will be
muggy; however, TD Nine is not the only relevant feature
complicating the forecast.
Major Hurricane Humberto rapidly intensified to a Category 5 north
of the Lesser Antilles yesterday, and an upper altitude trough is
digging south towards the Gulf over the eastern CONUS. Both of
these features will be influencing TD Nine over the next few
days. Trough and tropical cyclone interactions are very complex
and change based on the tilt of the trough, its distance to the
tropical cyclone, intensity of the tropical cyclone, and change in
trough orientation. The morning forecast tracks TD Nine to stay
offshore before it recurves into the Atlantic. The upper level
trough gets, for lack of a better word, pinched between a ridge
over the Great Plains and high pressure over the North Atlantic.
In this event, steering winds around TD Nine slacken and the
system slows down. Meanwhile, Hurricane Humberto keeps moving west
and weakening the Atlantic ridge. The combination of the decaying
trough and Humberto`s evolution would thus keep TD Nine offshore
and cause it to curve easterly. Copious rainfall is still forecast
for the eastern seaboard, but this forecast would keep the system
away from the Florida Keys.
In this scenario, what would the impacts from TD Nine be? Winds
will freshen and breezy conditions are likely across the island
chain. Shower coverage is forecast to peak this afternoon as TD
Nine makes its way north, and higher rainfall totals are expected
in the Middle and Upper Keys. Drier, continental air will move in
aloft over the Keys as TD Nine develops, which will limit shower
formation and depth during the first half of the week. Breezes are
not forecast to slacken back to gentle to moderate until the
second half of the week, and will remain westerly through at least
Wednesday. On the water, the heaviest swell will be felt off the
Upper Keys.
After TD Nine moves further away, the weather becomes less
certain. Interactions of three changing low pressure systems, one
of them a mid latitude cold core system, are extremely chaotic.
Expect a lot of updates to the forecast, because this a very
uncommon pattern for the Atlantic.
&&
.MARINE...
Issued at 421 AM EDT Sun Sep 28 2025
Small Craft Should Exercise Caution wording is in effect for all
the nearshore and offshore waters, though boats north of the
Middle Keys should exercise caution for increasing winds. From
synopsis, small Craft Advisories may be required across the
eastern waters this afternoon. Conditions across the Keys waters
will be defined by freshening breezes and increasing shower
coverage across the Florida Keys waters due to the proximity of
Tropical Depression Nine. TD Nine is forecast to track north-
northwest across the Bahamas through Monday before it curves east
into the Atlantic later in the week. Impacts to the Florida Keys
waters are expected to be moderate to fresh breezes and
northeasterly swells along the Upper Keys.
&&
.AVIATION...
(06Z TAFS)
Issued at 421 AM EDT Sun Sep 28 2025
VFR conditions will prevail at EYW and MTH through the 06Z TAF
period. Latest guidance keeps the terminals dry at least through
the mid morning hours. After this, there is the potential for some
shower and thunderstorm development across the area, but, whether
or not these occur near the terminals remains to be seen. VCSH
has not been included in the TAF due to low confidence in timing
and placement of this activity. Near surface winds remain north to
northeast between 3 to 10 knots this morning becoming northwest
to north this afternoon and evening.
&&
.CLIMATE...
In 2022, Major Hurricane Ian passed directly over the Dry Tortugas
overnight on September 27th and into the 28th. Ian moved N/NNE
through the western Straits of Florida on the 27th and began to
undergo an eyewall replacement cycle as it neared the Dry Tortugas.
Maximum sustained winds at the time Ian passed over the Dry Tortugas
were 120 mph. Sustained tropical storm force winds in the Lower Keys
began in the afternoon to evening hours on September 27th. Along the
island chain, moderate-to-strong tropical-storm-force winds impacted
the Lower Keys and adjacent coastal waters, and low-end tropical
storm force winds impacted the Middle and Upper Keys and adjacent
coastal waters. Island communities throughout the Florida Keys saw
widespread rainfall storm totals of 5 to 8 inches. The most
significant impacts came from Ians storm surge in the Lower Keys,
particularly on the south sides of Key West and Stock Island, where
major street flooding and significant flooding of homes occurred (>
100 homes flooded in Key West alone). Storm surge flooding extended
east into the Atlantic-side communities of the Lower Keys, with
flood waters entering many ground story enclosures. A combination of
high astronomical tides, a significant tidal anomaly (likely related
to the passage of major Hurricane Fiona over the Gulf Stream a week
before), storm surge in the right-front quadrant of Hurricane Ian,
and a combination of wind-driven wave setup and runup caused water
levels to peak at 3.0 to 4.5 feet above NAVD88 (approximately Mean
Higher High Water) along the southern sides of Key West and Stock
Island late Tuesday evening. A subsequent Gulf surge Wednesday
afternoon resulted in water level rises peaking 2 to3 feet above
NAVD88, resulting in flooding of low-lying streets and enclosures in
portions of the Florida Keys.
&&
.PRELIMINARY POINT TEMPS/POPS...
Key West  89  80  89  80 /  40  20  20  20
Marathon  89  79  88  80 /  50  30  20  20
&&
.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...None.
&&
$$
Public/Marine/Fire...AJP
Aviation/Nowcasts....BT
Data Acquisition.....BT
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NWS KEY Office Area Forecast Discussion