Area Forecast Discussion
Issued by NWS Key West, FL

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FXUS62 KKEY 230237

Area Forecast Discussion
National Weather Service Key West FL
1037 PM EDT Tue Jun 22 2021

A very weak mesoscale low pressure was evident on the visible
satellite imagery this afternoon and evening, south of the Lower
Keys. The system slowly moved northward and helped to enhance the
development of a line of thunderstorms north of the Lower Keys a
bit after 2200Z. The thunderstorms produced a copious amount of
lightning with little movement. Some of the storms affected the
Lower Keys producing rainfall amounts generally below half an
inch. Currently, the KBYX radar shows that most of the
thunderstorm activity has collapsed, even the storms that tried
to fire up as the outflow boundary coming from Cuba interacted
with the boundaries in the Lower Keys. The outflow boundary of
Cuban origins did manage to produce a wind gust of 24 knots at
Sand Key Light at 950 pm. Temperatures in the island communities
are in the lower to mid 80s and the dew point values are in the
mid 70s. Winds are light and variable.

The 00Z KEY sounding showed a moist profile with a precipitable
water value of 2.07 inches and ample CAPE. The temperature
inversion observed last night is no longer present. The dry air
has mixed out, moisture has increased and there are a few
boundaries out there that could help enhance the development of
convection. Thus, the rain chances have been increased to 30% for
the island chain, indicating a chance of showers and thunderstorms
for the overnight hours. Winds will be mainly southeast at 5 to
10 mph. Temperatures are expected to settle into the lower 80s
across the island communities during the overnight hours.


There are no watches, warnings, or advisories currently in effect
for the coastal waters of the Florida Keys. From synopsis, an
expansive high pressure cell from the western North Atlantic to
the southeastern United States will be the primary driver of local
winds and seas through the week. The shape and location of the
associated high pressure ridge across the Florida Peninsula will
fluctuate, resulting in east to southeast breezes undergoing peaks
and lulls across Florida Keys coastal waters, from this afternoon
through Saturday. Both rain and thunderstorm chances will
increase by mid-week, with winds and seas higher in and near
scattered thunderstorms, from Wednesday night through Friday.


VFR conditions will prevail at the Key West and Marathon terminals
through tomorrow evening. The storms that affected the Lower Keys
earlier this evening have subsided, but the activity may increase
again during the overnight hours. Time and location is uncertain,
thus expect possible amendments. Also, a cumulus cloud line may form
late tomorrow morning or early afternoon. VCTS has been added to
the TAFs for both terminals, and TEMPOs may be required as the
activity develops. Winds will be mainly southeast at 5 to 10


On this date in 1990, Marathon recorded a record rainfall of 4.30
inches. This is also the wettest day ever recorded in the Marathon
area for the month of June. Rainfall records date back to 1950.


Key West  81  89  80  88 / 30 30 50 50
Marathon  81  90  80  88 / 30 30 50 50




Data Acquisition.....DDR

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