Area Forecast Discussion
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FXUS62 KKEY 180736

Area Forecast Discussion
National Weather Service Key West FL
336 AM EDT Wed Sep 18 2019

A few lonely showers have managed to develop this evening and
overnight despite the drier lower tropospheric air seen on the
Key West evening sounding. Otherwise, radar has been essentially
clear of returns. A wind surge developed during the evening hours,
maybe aided by the mainland density current, but winds have begun
to relax over the past hour or so and veer slightly east of
north. Satellite imagery shows a few cumulus over the Straits and
Hawk Channel, but basically cloud free over the islands and Gulf
waters. Dewpoint temperatures briefly touched 70 at the WFO Key
West RSOIS during the height of afternoon mixing, but have since
recovered to the mid 70s. Hopefully a harbinger of things to come,
as the MEX guidance is showing dewpoints dropping into the upper
60s after this weekend. The European MOS guidance shows mid 70
dewpoints through the forecast period. More on this to follow.

With the aforementioned drier air remaining in place, convection
will struggle to develop today and this evening. However, a few
showers did develop last night, so will leave a slight chance in
the forecast. A wind surge is expected to build in from the
northeast as the ridge along the CONUS east coast builds into the
area. The resultant speed convergence, especially in the Florida
Straits, will likely serve as an impetus for convective
development. With the surge of wind, advisory criteria may be
reached in our Florida Straits waters this evening, and
overspread the area over the next couple of days. This general
scenario will continue through Thursday evening.


For the remainder of the forecast period, through Tuesday, the
Keys and coastal waters will be under the influence of the strong
ridge along the east coast and eastern seaboard. While conditions
will remain fairly dry through Thursday evening, that will begin
to change rather dramatically beginning Friday as a significant
moistening of the troposphere takes place. Rain chances will
remain in the high chance neighborhood through the weekend. On
Sunday evening a backdoor weak boundary will push through,
bringing the driest air since the beginning of the wet season.
This is what could potentially drop dewpoints into the upper 60s
Sunday evening through Tuesday. During this period, will hedge on
Pops and remain near climo, but this may be wildly overdone
considering the drying and subsidence forecast. All of this, of
course, is continent on the longer range models coming to


Gently to moderate northeasterly winds will prevail through this
afternoon. Beginning late afternoon into this evening, winds will
begin to surge out of the northeast, with winds increasing to
moderate to fresh. A small craft advisory may be required this
evening for Hawk Channel and the Florida Straits. The higher winds
will slowly overspread the area, and persist into this weekend as
high pressure continues to build into the area from the north.


VFR conditions will prevail at both terminals through this
afternoon. North winds at the terminals will become northeast by
afternoon and increase to near 10 knots sustained with gusts
approaching 20 knots in the evening hours as high pressure
building into the region. FEW to SCT clouds at FL025 to FL030 with
slight chance of a passing shower possible at either or both


Key West  90  80  87  78 / 20 20 30 30
Marathon  90  79  88  78 / 20 20 20 20




Data Collection......99

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