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Area forecast discussion for the Florida Keys 
National Weather Service Key West Florida 
930 am EST Sat Nov 21 2009 


Discussion...in the middle and upper levels...700-200 mb...latest 
water vapor available satellite imagery overlaid with streamline 
analysis as of 9 am continue to depict a split flow pattern across 
the Continental U.S.. a near 100 knot jet at 250 mb traverses the southern 
portion of North America as it moves across Baja California...northern 
Mexico...then northeastward to the Carolinas. A disorganized upper 
low over Oklahoma dives the northern stream from the southern stream 
of the of the jet. The Florida Keys are beneath a wide band of the 
southern jetstream...with cirrus moving overhead 


In the lower to middle levels...surface to 700 mb...latest infrared 
satellite imagery overlaid with available surface and marine 
observations detail a 1008 mb low over the northwestern Gulf of 
Mexico. A warm front is analyzed eastward toward the Florida 
Peninsula...while a cold front swings south from the system to 
central Mexico. As a result...the 12z sounding this morning 
illustrates a gentle but moistening east to southeast flow from the 
surface to about 10000 feet...with pwat(precipitable water) that has 
risen in 24 hours from 1.46 inches or almost 1.5 inches from only 
1.08 inches yesterday morning. Enough isentropic lift is available 
along the 300k surface...with isolated showers delivering brief 
periods of light rain falling from cloud bases between 4000 and 5000 
feet. 


Currently...as of 900 am...skies are partly cloudy over the islands 
and adjoining waters. Key West radar scans show a dwindling area of 
light showers confined to the waters within 30 nm offshore of the 
Florida reef between Sombrero Key light and east Sambo light. 
Temperatures are presently in the middle to upper 70s with dewpoints in 
the lower 70s. C-man stations along the reef are registering 
northeast to southeast winds around 10 knots...except 10 to 15 knots 
out at Pulaski Shoal light. 


Short term (rest of today)...in the middle and upper 
levels...(700-200 mb)...all large scale models slide the low 
pressure area over the Southern Plains eastward and fill a few 
decameters through 00z. Just a few cirrus clouds will be transported 
over the Keys through the day. 


In the lower to middle levels...surface to 700 mb...the weak surface 
low over the northwest Gulf will continue to move northeastward to 
just off the Louisiana coast by days end. Dryer air in the middle 
levels will gradually filter across the Keys from the east later 
this morning...putting an end to any chance for measurable rain 
today. Temperatures and humidity levels will continue to be slightly 
above normal...reaching into the lower 80s. Will just do a last 
minute update this morning to take out transitional wording and 
remove shower threat over the islands. 


&& 


Marine...light to gentle winds will increase to gentle to moderate 
this afternoon and tonight 




&& 


Aviation...through 22/12z...prevailing VFR conditions are expected 
at eyw and mth. A few light showers in the vicinity of eyw this 
morning should dissipate by 15z. 




&& 


Key watches/warnings/advisories... 
Florida...none. 
GM...none. 
&& 


$$ 


Public/marine/grids............futterman 
aviation/nowcasts..............kasper 
data acquisition/upper air.....Ross 




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