616
FXUS62 KKEY 110942
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
542 AM EDT Tue Jun 11 2024

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

.DISCUSSION...
Issued at 542 AM EDT Tue Jun 11 2024

Convective activity has ramped up across the Florida Keys forecast
area overnight. KBYX is detecting scattered light to moderate
rainfall, with a few embedded heavier showers. Earlier, a strong
thunderstorm moved across Carysfort Reef Light and produced a wind
gusts of 46 mph. Winds have picked up a few knots higher than
expected in the western coastal waters and across the Lower Keys,
and the Sand Key C-MAN station is reporting gusts of 22 knots.

The upcoming week is proving to be quite a tricky forecast, as
evidenced by the lack of measurable rainfall in most island
communities overnight. Last night`s sounding sampled all of the
necessary parameters (i.e. high CAPE, virtually no inhibition, and
well above normal moisture), but rainfall has been scarce along
the island chain. This has likely been due to the diffluence
across our area thanks to a low-level ridge axis extending across
the Bahamas and South Florida. The diffluence at the surface can
still be seen, with a southeast to south wind direction at Sand
Key and a southwest wind direction at Carysfort. This ridging will
be one of the factors causing the above normal uncertainty in the
forecast over the next few days. Despite any uncertainties, the
knowns in the forecast are pointing to a wet few days of weather
for the Florida Keys. The generally synoptic set is a broad trough
(Central American Gyre) pushing deep tropical moisture into the
region for the remainder of the week. A stalled front, currently
lingering along the Gulf Coast, will remain stalled with maybe a
little southward movement through the week. This front will act to
keep moisture trapped across the Gulf for a prolonged period. The
Weather Prediction Center has placed the entirety of South
Florida and the Florida Keys in a Slight Risk (level 2 of 4) of
excessive rainfall today through Friday due to the extended stay
of this tropical moisture plume.

Now let`s talk uncertainties...As previously mentioned, winds have
already jumped to above what was expected. Guidance suggests that
these winds should start to decrease by this afternoon, so have
issued a Small Craft Advisory for the western waters through at
least later this morning. Just how far these stronger winds will
extend eastward and their exact magnitude for the remainder of the
day is a little fuzzy, and amendments to the wind forecast may be
necessary if anything drastically changes. In terms of rainfall,
model guidance is suggesting that we will become weakly confluent
later this morning. This confluence combined with a forecasted
25-30 knot steering flow and well above normal PW should, in
theory, lead to widespread rainfall. The best confluence will be
to our north, so we could see a rather dramatic rainfall gradient
across our area. This environment will generally remain in place
through the end of the week, so have kept rain chances at likely
to categorical (60-80%) through Friday. Have also decided to issue
a Flood Watch for the entire Florida Keys with the expected
rainfall. With the uncertainties involving stark gradient that
will likely set up somewhere in our area, have only issued the
Flood Watch through Wednesday night at this time. Depending on the
evolution of the environment over the next 36 hours, this watch
may need to be extended through the remainder of the week.

By the start of the weekend, ridging will begin to build back in
and shove the best moisture to our west. Rain and thunder chances
will finally begin to diminish beginning on Saturday night, but
will still remain slightly above normal through the extended
forecast.

&&

.MARINE...
Issued at 542 AM EDT Tue Jun 11 2024

A Small Craft Advisory was issued for the western coastal waters
including the western Straits, western Hawk, and Gulf waters
including the Dry Tortugas. Elsewhere besides the Florida Bay,
small craft should exercise caution until winds decrease. From
synopsis, the pattern this week will feature weak high pressure
over the western North Atlantic and a frontal boundary stalled
over northern Florida. Although, the main weather maker will be a
large cyclonic gyre centered over Central America. As such,
moderate to fresh breezes and an extended period of unsettled
weather featuring thundery squalls will persist today through
Friday night. Rain and thunder chances will decrease gradually
starting Saturday.

&&

.AVIATION...
(06Z TAFS)
Issued at 542 AM EDT Tue Jun 11 2024

Showers and thunderstorms began developing in waters surrounding the
Florida Keys before 7Z, but active weather transitions between VFR
and potentially IFR conditions will dominate the TAF period. Current
observations and hi-res model guidance suggests VCSH conditions at
the terminals will begin before sunrise. Showers are expected to
approach EYW and MTH in waves as a mixture of VCSH and VCTS
throughout the TAF period. Expect rapid deterioration in flight
conditions when heavy showers and lower CIGs move ashore. The timing
the approach of individual thunderstorms is extremely uncertain,
resulting in the absence of TEMPOs from the TAFs. Prevailing near-
surface winds will remain southerly to later southwesterly within a
range of 10 to 15 knots and gusts between 20 and 25 knots, but gusts
may approach 35 knots near showers.

&&

.CLIMATE...
On this day in 1999 in Keys weather history, the daily record
rainfall of 2.50" was measured at Key West. Local climate report
says the rain fell in less than three hours, and the associated
thunderstorms produced wind gusts of 50-60 mph that minor damage
on Stock Island. Rainfall records for Key West date back to 1871.

&&

.PRELIMINARY POINT TEMPS/POPS...
Key West  88  79  87  80 /  80  80  80  60
Marathon  88  80  87  80 /  80  80  80  60

&&

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...Flood Watch through Wednesday evening for FLZ076>078.

GM...Small Craft Advisory for GMZ033>035-044-054-055-074-075.

&&

$$

Public/Marine/Fire...NB
Aviation/Nowcasts....AJP
Data Acquisition.....AJP

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