Area Forecast Discussion
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FXUS62 KKEY 270901

Area Forecast Discussion
National Weather Service Key West FL
501 AM EDT Thu Oct 27 2016

.DISCUSSION...A deep layered ridge centered over the South Atlantic
Bight supports expansive high pressure across the extreme eastern
United States and the western North Atlantic. A tight pressure
gradient persists across the Bahamas, the Gulf of Mexico, and the
Western Caribbean. Strong northeast to east breezes prevail at the
marine observation platforms. Most land stations appear to be
decoupled from the 25 knot flow sampled by the KBYX radar at 1 kft.
However, periodic gusts to 25 mph have been widespread across the
island chain. Temperatures are in the lower to mid 70s with dewpoints
near 70. Mean layer analyses from CIMSS place a long wave trough
complex deep into the tropics, bisecting southern Mexico. Several
short wave impulses have infused and phased this feature into a
formidable anomaly. Water vapor and infrared satellite imagery
highlight the expansive leaf-like cloud shield to the east of this
upper level trough. Deep convection has remained near the core of
the trough and well to the west of coastal waters of the Florida
Keys. The KBYX radar detects widely scattered showers which have
periodically wetted the island chain. Showers have not been very tall
and appear to be struggling against the inversion near 700 mb (see

.FORECAST...We have retained the cloudy and windy conditions for
today and tonight, and agree with the 70% rain chances. The upper
levels will provide favorable venting aloft, meanwhile, 925-700 mb
wind vectors indicate 25 to 30 knots of low level easterly mass
transport. Forecast soundings continue to depict 15 to 20 knots of
veering flow between the intake and exhaust, evidence of a short wave
impulse. Thus, the coupled atmosphere should produce numerous
showers and isolated thunderstorms this afternoon and into the first
half of tonight. Thereafter, the Florida Keys will remain on the
cusp of deep tropical moisture to our south, and a maritime-
modified, continental airmass to our north. Baroclinic episodes along
this boundary will be successful in producing precipitation. The
trend over the past few days has been for increased rain chances
Friday night through Sunday. Once again, we have retained the 40%
chances for these periods. The enhanced low level gradient will relax
somewhat Sunday through Monday, however, breezy conditions will
persist. Low level northeasterly trajectories accompanied by
continental infusions Monday through Wednesday will result in lower
humidity and slight rain chances.


.MARINE...A Small Craft Advisory remains in effect for all Florida
Keys coastal waters zones. Sustained northeast to east winds near 25
knots with occasional gusts near 30 knots are expected today. Seas
will remain as high as 8 feet across portions of the extreme
southeastern Gulf of Mexico beyond five fathoms, while seas of 9 to
12 feet persist in the Straits of Florida. Higher and steeper waves
will occur in the Gulf Stream, where wind-generated waves oppose the
current. Breezes will slacken somewhat Sunday through Monday.


.AVIATION...The atmosphere will continue to moisten across the Keys
today. The deeper moisture will combine with an upper level
disturbance to produce numerous showers across the area late this
afternoon/evening. Will mention VCSH in the TAFs through 20Z then
categorical shower activity from 20-22Z through 06Z Friday. A few
lightning strikes will be possible this period as well. Brief periods
of MVFR ceilings and brief wind gusts around 30 knots will be
possible in the showers as well. Outside of rainfall activity, east
winds 12-15 knots with gusts 20-25 knots are expected. Sky cover will
mainly stay in the VFR range. 34/MM


Key West  83  75  83  75 / 70 70 30 40
Marathon  83  76  84  77 / 70 70 30 40


GM...Small Craft Advisory until 5 PM EDT this afternoon for


Data Collection......Vickery

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