Area Forecast Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS62 KKEY 201743

Area Forecast Discussion
National Weather Service Key West FL
143 PM EDT Sat Jul 20 2019

Shower coverage has increased slightly from this morning along
the islands and nearshore waters, but still remains isolated in
nature. A thunderstorm or two appears likely, especially north of
the lower Keys where a surface convergence zone appears to be
setting up off cloud streamers from the islands. Winds have
remained steady through the day from the east southeast, with near
10 knots along the reef and 5 to 10 knots along the island chain.
A recent ASCAT pass clipped the outer Straits east of the upper
Keys, finding winds in the 10 to 12 knot range.

Showers and thunderstorms should begin to proliferate in the
Straits this evening and overnight as the weak wave near Andros
island slowly progresses westward. By Sunday, showers and storms
will begin to overspread the Islands and Gulf waters. Rain
chances have been increased to likely on Sunday to reflect the
increase, and to be more consistent with current MOS guidance and
forecast reasoning. Sunday night through Monday rain chances will
begin to slowly taper off towards climatology, and will hold near
climo if not slightly lower into Wednesday.


A relatively high amplitude trough begins to push towards the
eastern seaboard beginning Monday night/Tuesday. This should
disrupt the Atlantic ridge and serve to push the ridge axis
towards the south, over the Keys and coastal waters. The light
winds resulting from the weak gradient over the area will produce
a favorable environment for mesoscale processes through Friday,
such as cloud line convection along the islands. Later in the
week, basically from Wednesday evening though the end of the
forecast period, rain chances will drop off rather precipitously
as drier air will filter into the mid-levels and precipitable
water drops well below climatology. It remains to be seen if this
will inhibit mesoscale effects along the islands, so there is a
little hesitation to drop rain chances too dramatically from
Tuesday though Thursday. Considered removing lightning entirely
from Thursday to Friday, but will hold on to isolated storm
coverage for now.


Mostly gentle east southeast breezes are anticipated over all
Florida Keys coastal waters through tomorrow. However,
thunderstorm coverage will increase overnight through tomorrow
evening, and mariners can expect higher winds and seas in the
vicinity of thunderstorms.


VFR conditions are expected at both the Key West and Marathon
terminals through this evening. Near-surface winds will remain from
the southeast at 5 to 10 knots. FEW to SCT cloud bases at or around
FL025 are expected through 06z. Thereafter, BKN conditions with
similar cloud bases and VCSH are anticipated at both terminals.


Key West  80  88  80  90 / 50 60 40 40
Marathon  80  90  80  92 / 50 60 40 40




Data Collection......Chesser

Visit us on the web at

Follow us on Facebook and Twitter at: is the U.S. government's official web portal to all federal, state and local government web resources and services.