Area Forecast Discussion
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FXUS62 KKEY 231844

Area Forecast Discussion
National Weather Service Key West FL
244 PM EDT Sun Jul 23 2017

Recent satellite-derived total precipitable water measurements
indicate slowly increasing values across the service area,
particularly between the Cay Sal Bank and Florida Bay. Indeed,
this is the area where local Doppler radar data are indicating
isolated showers moving northwestward near 8 knots. A weak
southeasterly low-level flow prevails across the Florida Keys and
adjacent coastal waters, on the southwestern flank of a deep
subtropical anticyclone centered over the western North Atlantic.
The associated low-level ridge is just north of the Florida Keys,
while the mid-level ridge remains just south of the Straits of
Florida. Most of the aging Saharan Air Layer plume has shifted
west of the area, and skies over the Keys today are much less
milky looking than yesterday. Currently, air temperatures in most
Keys island communities are near 90F, with dewpoint temperatures
in the mid 70s and heat indices ranging from 98F to 103F. Light
to gentle southeasterly breezes prevail.

It will take another 12-24 hours for tropospheric moisture to
return to what it was a few days ago, so we will maintain
20-percent measurable rain chances for one more period.
Thereafter, we are staying with 30-percent chances through the
forecast horizon, which is very near late July/early August
climatological relative frequencies. The Atlantic subtropical
anticyclone will be the dominant weather system for Florida Keys
weather this week. Both position and intensity will fluctuate
somewhat, as will the depth of the moist layer locally. Mesoscale
circulations arising from differential heating and deep cumulus
convection will drive convective initiation each day and night.
Wind speeds should remain below 15 mph outside of showers and

A high pressure cell will extend westward from the subtropical
North Atlantic to the Gulf of Mexico from tonight through Friday.

VFR conditions will prevail at both the Key West and Marathon
terminals thru 18z/24. Atmospheric moisture will increase
overnight and Monday morning, resulting in an increase of shower
coverage, which could result in episodes of MVFR VIS/CIGs after
12z/24 at either terminal. Winds will remain light and
southeasterly at less than 10 knots through the forecast period.

On this date, back in the year 1900, the daily record rainfall of
2.06" was recorded. Key West has not seen a daily rainfall in
excess of 2.00" since June 7th, when 4.39" was observed. July is
typically the 5th wettest month of the calendar year, averaging
3.55" of rain. Rainfall records date back to 1871.

Key West  83  90  83  91 / 20 30 30 30
Marathon  83  92  83  92 / 20 30 30 30



Data Collection......Fling

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