Area Forecast Discussion
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FXUS62 KKEY 200136

Area Forecast Discussion
National Weather Service Key West FL
936 PM EDT Fri Apr 19 2019

Squall line continues to work slowly eastward through the Lower
Keys this evening, with a few clusters of showers and storms also
developing out ahead of the main line. Strongest wind gusts
observed so far have been 39 kts at Smith Shoal Light Weatherflow
and 35 kts at Pulaski Shoal C-MAN. Activity has generally weakened
recently across the Keys and adjacent waters, while remaining
stronger to our north across the Miami/Fort Lauderdale metro area.
Surface analysis shows the cold front extending from near
Melbourne to south of Naples to east of the Dry Tortugas. GOES
derived total PW satellite imagery shows a much drier airmass
filling in behind the front, and surface dewpoints have already
dropped into the 50s as far south as Fort Myers. The 00Z Key West
sounding unfortunately got drawn into the line of thunderstorms
just west of the station at release time, and only made it up to
560 mb before terminating. The 00Z Miami sounding depicted moist
and unstable low/mid levels, with PW of 1.80 inches.

Overnight, showers and storms will continue moving eastward
through the Keys and surrounding coastal waters. Primary weather
concerns will be frequent lightning strikes, gusty winds and
locally heavy rains. Wind gusts observed thus far and recent radar
trends suggest that strongest wind gusts should remain below 40
mph, but there is always the possibility that an isolated stronger
storm could develop. We will need to monitor rainfall totals, as
redevelopment of showers and storms over the western Lower Keys
has already produced rainfall totals approaching an inch at Key
West. Rainfall will taper off across the Lower Keys by midnight,
with the heaviest rains expected across the Middle and Upper Keys
generally between 11 PM and 3 AM. Forecasts will be updated
shortly to reflect the slower eastward progression of the
convection. We still expect rapidly improving conditions late
tonight and on Saturday, with clearing skies along with a cooler
and notably drier airmass.


Small Craft Advisory in effect tonight for all coastal waters of the
Florida Keys due to west to northwesterly winds near 20 knots. A
squall line associated with an expected cold front is currently
moving east through the island chain and will clear the Upper Keys
after midnight. Behind the squall line, fresh northwest breezes will
slowly diminish towards sunrise Saturday. High pressure over the
western Gulf of Mexico on Saturday will spread east across Florida
by Sunday night. As a result, breezes will turn to the north then
northeast, diminishing appreciably Saturday night and Sunday.
Despite the diminished breezes, large westerly swells will persist
across the western half of the coastal waters of the Florida Keys,
including the Straits of Florida, portions of the Reef Tract, the
southeastern Gulf of Mexico, and Gulf side waters inside five
fathoms. A high pressure ridge will persist across north Florida
from Monday through Wednesday, maintaining moderate easterly


Thunderstorm and heavy rain impacts at the EYW terminal should
end around 02Z, while thunderstorm/rain impacts at the MTH
terminal are expected between 03Z and 05Z. Periods of MVFR or IFR
conditions are likely during these times, along with wind gusts up
to 30 knots from the west. Improving conditions are expected at
both terminals late tonight as the cold front moves through, with
winds turning to the northwest. VFR conditions and NW winds of 10
to 15 knots with gusts up to 20 knots are expected from the
predawn hours on Saturday through the day.


GM...Small Craft Advisory for GMZ031>035-042>044-052>055-072>075.



Data Collection....SD

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