757
FXUS62 KKEY 170920
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
520 AM EDT Tue Sep 17 2024

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

.DISCUSSION...
Issued at 515 AM EDT Tue Sep 17 2024
The stillness of yesterday evening following the dissipation of a
few cloud lines has been broken this morning. Outflow boundaries
ejected from late evening Cuba convection drifted north through
the Straits of Florida with very little fanfare. That changed as
it crossed the island chain and exploded with a handful of
thunderstorms arranged in a broken line. As of writing this
discussion, these storms are currently ongoing with more bubbling
further down the boundary in the northern waters of the Keys.
Despite the spark of unsettled weather, most island communities
have yet to see precipitation this morning (with the exception of
portions of the Upper Keys at this moment). Temperatures are
floating around the mid 80s with near 80s over areas with ongoing
rain. Light to gentle breezes are stubbornly out of the south
along the Reef and likely aiding in convergence with more stagnant
air north of the island chain.

This morning is just a preview of conditions expected in the short
term forecast. As the low pressure that was Potential Tropical
Cyclone 8 continues to sync with the upper level trough over the
southeast CONUS, deep layer troughing will establish itself over
Florida. This will not only allow deep tropical moisture to
advect into our area but provide decent synoptic upper level
support to prospective thunderstorms. On the other hand,
background flow will remain light with no organized lift sources
in sight. Clearly this is somewhat of a non-issue as storms have
initiated just fine with the left over boundaries from yesterday
resulting in what could be described as a mesoscale feast.
Surprisingly, several CAMs runs have done a decent job capturing
the mode and location of ongoing convection, even if it was an
hour late or so. We expect storms to percolate throughout the
short term only finding some lulls in activity to recharge the
atmosphere and find its next source of lift. Likely PoPs are held
into tomorrow as a result, but may need to be adjusted with the
timing of the previously mentioned lulls overnight.

By the end of this week PoPs will stabilize back near normal as
the deep layer troughing slides northeast up the Eastern Seaboard.
Left with no strong synoptic influence of sensible weather,
conditions will return to a normal late wet season regime. Light
and at times variable breezes will persist through the weekend.
Some guidance suggests a slight dip in dewpoints around the start
of the weekend due to the passage of the stationary front
currently parked over Central Florida, but its certainly not going
to bring any early fall weather with it. PoPs will remain near
normal, if not a touch higher, for the remainder of the extended
period.

&&

.MARINE...
Issued at 515 AM EDT Tue Sep 17 2024
From synopsis, light and generally variable breezes will continue
through Saturday across the Florida Keys coastal waters. Winds
and seas will be elevated in and around thunderstorms,
particularly on Tuesday and Wednesday, though background winds
will remain light and variable. Northerly swell generated by the
low pressure on the Eastern Seaboard will linger through Tuesday
and Wednesday. This disturbance will deepen into an upper level
trough and slowly slide south towards the Florida Peninsula
through Saturday. Unpredictability in the movement of this trough
means confidence in the extended forecast is very low.

A Coastal Flood Advisory remains in effect for the Upper Keys,
and a Coastal Flood Statement remains in effect for the Middle and
Lower Keys. Boaters can expect less clearance under fixed bridges.

&&

.AVIATION...
(06Z TAFS)
Issued at 515 AM EDT Tue Sep 17 2024
A mix of showers and thunderstorms will persist across the area this
morning and afternoon, so VCSH will be maintained in the TAFs for
both island terminals. The timing related to individual stronger
cells moving over either site is still in question though, so
amendments will be issued as warranted. In general, VFR conditions
should prevail into the early morning, but once these showers and
thunderstorms become more widespread in coverage, MVFR CIGs will
likely prevail with intermittent periods of IFR and LIFR CIGs and
VIS from stronger cells. Prevailing winds will remain southeasterly
at 5 to 10 knots, but occasional erratic gusts may stem from any
given cell.

&&

.CLIMATE...
On this day in Keys weather history in 1985, the daily record low
temperature of 69F was recorded at Key West International Airport.
This also tied for the coldest temperature ever recorded in
September.

&&

.PRELIMINARY POINT TEMPS/POPS...
Key West  90  81  90  81 /  60  60  60  40
Marathon  90  81  90  81 /  60  60  60  40

&&

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...Coastal Flood Advisory until 5 PM EDT this afternoon for FLZ076.

GM...None.
&&

$$

Public/Marine/Fire...JAM
Aviation/Nowcasts....DP
Data Acquisition.....DP

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