Area Forecast Discussion
Issued by NWS
FXUS62 KKEY 261904
Area Forecast Discussion
National Weather Service Key West FL
304 PM EDT FRI AUG 26 2016
.DISCUSSION...A deep anticylonic gyre remains centered over the
southeastern United States. The accompanying surface ridge axis
reaches west towards the Atlantic Bight. A weak area of low pressure
is located between the northeastern coast of Cuba and the central
Bahamas. This wave in the easterlies is moving west- northwest,
parallel to the cuban coastline. Loops from MIMIC TPW imagery
describe a plume of tropical moisture across the Western North
Atlantic. This is corroborated by this morning`s KKEY RAOB which
sampled precipitable water above the 90th percentile, with easterly
winds extending through 20 kft. The profile was moderately unstable
with limited inhibition in the boundary layer. Visible satellite
imagery reveals a nodular cloud line, favoring discrete thunderstorms
as opposed to a line of showers. Temperatures have reached near 90
with dewpoints near 80. Moderate east-northeasterly breezes prevail
at the coastal observation stations.
.SHORT TERM (TONIGHT THROUGH SUNDAY NIGHT)...Persistence is a
valuable forecast tool when the atmosphere remains unchanged. The
afternoon sea breezes of South Florida should be very successful in
producing convection over the next couple hours. These showers and
storms should emigrate to the bayside and gulf side waters this
evening. An evening surge in the easterlies should complicate
matters, feasting on residual boundaries from the afternoon cloud
line and South Florida convection. The tropical wave will work west-
northwest towards the Florida Keys and South Florida Saturday through
Sunday. As it nears, low level flow will become weakly cyclonic,
weakly convergent, sufficiently moist, and chock full of initiation
sources. We advertise increasing rain chances through the short term,
culminating in numerous showers and scattered thunderstorms Sunday
night. Cloud cover will be extensive. Temperatures may be a few ticks
below what they have been.
.LONG TERM (MONDAY THROUGH FRIDAY)...The wave will move northwest
into the Gulf of Mexico Monday through Tuesday. Through five days,
the National Hurricane Center gives this system a 60% chance for
development into a tropical system. A strengthening low would result
in winds higher than forecast, especially given isallobaric responses
in the gradient wind. Additionally, a sloppy, confluent, and moist
southeasterly flow should retain higher than normal rain chances on
the back side of the system. Wind speeds and rain chances should
decrease by Wednesday, with the Western Atlantic Ridge building west
across the Keys thereafter.
.MARINE...No current watches, advisories, or warnings. A weak low
pressure system, sometimes referred to as a tropical wave, will move
through the coastal waters of the Florida Keys Sunday and Sunday
night. Fresh easterly breezes will shift to the southeast, then
south, as the wave axis passes. Small Craft Advisories may be
required Sunday night through at least Monday night as the
disturbance moves into the Gulf of Mexico.
.AVIATION...Rest of today...Showers and thunderstorms will refire
again this afternoon within a cumulus/towering cumulus cloud lines.
Additional showers and storms over the southern tip of the Florida
peninsula and Florida Bay will interact with these existing cloud
lines. These boundaries will fire up episodically overnight when they
collide. Short period MVFR/IFR cigs and/or VIS will likely occur in
showers and thunderstorms that impact any or both of these terminals.
Amendments will be issued as necessary.
On August 26 1956, the temperature in Key West hit 97 degrees. This
is the warmest temperature ever recorded in Key West in August, and
is tied for the highest temperature ever recorded in Key West.
Temperature records for Key West date back to 1872.
.PRELIMINARY POINT TEMPS/POPS...
Key West 82 90 81 89 / 40 40 40 50
Marathon 82 90 81 89 / 40 40 40 50
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