421
FXUS62 KKEY 190807
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
407 AM EDT Sun May 19 2024

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

.DISCUSSION...
Issued at 407 AM EDT Sun May 19 2024

Despite being a relatively quiet night across the Florida Keys,
KBYX is detecting some of the first showers we have seen within
our forecast area in the past few days. All of these showers have
remained offshore in the SE Gulf, so there has been no measurable
rainfall along the island chain. GOES Nighttime Microphysics is
detecting mostly clear to partly cloudy skies across the forecast
area, with a combination of both low level cumulus and upper level
cirrus. Temperatures remain in the lower to mid 80s early this
morning and dew points are in the upper 70s to near 80, leading to
heat indices between 95-100 degrees. With winds trending
downward over the past hour or so, the oppressive humidity is
becoming even more apparent, if that is even possible...

Another day of above normal heat is on tap for the Florida Keys.
While MOS guidance is suggesting dew points a degree or two lower
than what we have been experiencing the past few days, have
decided to issue another heat advisory for today. The synoptic
feature that has been responsible for this oppressive mid-May heat
is an expansive mean layer ridge that has been parked over us.
This high will finally get shoved eastward starting today as a
longwave trough traverses across the Southeast. The front
associated with this trough will slide down the Florida Peninsula
over the next few 122days. As this front travels down the state,
model guidance depicts moisture pooling across the Keys and South
Florida. While the best upper-level support is forecast to remain
to our north, rain and thunder chances are forecast to increase
tonight. There is still a large amount of discrepancy between
models in terms of PoPs, with the ECMWF coming in much wetter
than the GFS. As a result, there is an unusually large amount of
uncertainty in the near-term forecast. Have decided to split the
difference and kept mid-chance PoPs for tonight through Tuesday.
Thereafter, rain and thunder chances will return closer to normal
(~20%) as mid-level dry air invades. Low-level moisture will
remain in place during this time, allowing for mesoscale processes
to dominate within the light wind regime forecast for the next
week.

In terms of temperatures and dew points through the extended
forecast, winds will shift to the northwest to north ahead of the
aforementioned front this evening. This will bring in lower dew
points and help drop temperatures a degree or two beginning
tonight. Temperatures through the work week will generally be
hovering around the climatological norm, with dew points forecast
to be in the lower to mid 70s. This will put us out of Heat
Advisory criteria and bring us back to our regularly scheduled
May.

&&

.MARINE...
Issued at 407 AM EDT Sun May 19 2024

There are no watches, warnings, or advisories in effect for the
Florida Keys coastal waters. From synopsis, the western extent of
a low-level ridge axis that extends west-northwest has begun to
lose its grip across the Florida Keys, and breezes have shifted to
the southeast to south. Breezes will quickly veer to the north
and decrease today as a frontal boundary slides down the Florida
peninsula. There may be a break in the rain-free conditions
tonight through Tuesday, followed by variable breezes turning to
the east Wednesday through Thursday.

&&

.AVIATION...
(06Z TAFS)
Issued at 407 AM EDT Sun May 19 2024

VFR conditions will prevail at both EYW and MTH today and early
tonight. While there is a slight chance of showers today, they will
be isolated at best with low confidence in exact location so VCSH is
left out of either TAF for now. Tonight, scattered showers and
isolated thunderstorms are expected to develop along the island
chain and persist into tomorrow morning. As the timing isn`t set in
stone yet and is just on the far edge of the TAF period, no mention
is expressed in this morning`s TAFs. Near surface winds will start
out of the southeast to south at near 10 knots this morning,
becoming west to northwest later this afternoon.

&&

.CLIMATE...
Yesterday, May 18th, the low temperature at both Key West and
Marathon was 84F. This broke daily record warm low temperatures at
both sites. At Marathon, this low temperature tied the highest
warm low ever recorded in May in Marathon (current record that
was tied: 84F, 2017), and broke the highest warm low ever recorded in
May in Key West (previous record: 83F, 2024, 2020, 2017).
Temperature records date back to 1872 in Key West and 1950 in
Marathon.

&&

.PRELIMINARY POINT TEMPS/POPS...
Key West  91  80  88  79 /  10  40  30  40
Marathon  91  80  88  79 /  10  40  30  40

&&

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...Heat Advisory from 10 AM this morning to 6 PM EDT this evening
     for FLZ076>078.

GM...None.
&&

$$

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

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