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Area Forecast Discussion (AFD)

Issued by Key West, FL (KEY)

                            
000
FXUS62 KKEY 190823
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
423 AM EDT Fri Oct 19 2018


.DISCUSSION...In the middle and upper levels( 700-200 mb), latest
available GOES-R satellite imagery overlaid with model streamline
analysis as of 300 am, depict the 595 decameter center of an 
expansive warm core middle and upper level anticyclone positioned 
from the North Central Gulf of Mexico just south of the Delta to 
across Central Florida into the Western Atlantic near 24N 64W. To
the north of this feature, there is a zonal progressive low 
amplitude averaging 75 to 100 knot flow at 250 mb, evident from 
the NW Old Mexico northeastward to the Midwest thence east 
southeastward to the Middle Atlantic Coast.

At the surface and in the lower to mid levels(Surface to 700 mb),
latest available GOES-R satellite imagery overlaid with marine 
and land surface observations and surface analysis, depict the
center of cold 1030 mb plus surface anticyclone centered over
Southern Ohio. Well south of that, a stationary front is draped
across the northern 1/3 of the breadth of the Gulf to across
Northern Florida into the Western Atlantic Ocean. As a
result, last evenings 00Z sounding at KEY illustrated a fresh
northeast flow from off the surface to 850 mb, becoming moderate
above that up to about 700 mb, then veering back to between east
and southeast up to 300 mb. Overall column was still similar to 24
hrs prior, with PWAT at 1.34 inches. Upstream of South Florida and
the Keys, GOES TPW really continues to delineate the drier air, 
averaging between 1.00 and 1.25 inches out to the 60th Meridian. 

.CURRENTLY...As of 300 am, skies are mostly clear across the
islands and surrounding waters, with only a few showers dotting
the far outer SW Straits. Temperatures are right near 80 degrees
with dewpoints in the lower to mid 70s. C-man stations along the
Florida Reef are mostly east at 15 to 20 knots to around 20 knots,
with near 20 knots at Smith Shoal Light. An ASCAT pass late last
evening at 200Z showed solid 20 plus knotters in the Central and
Western Florida Straits. Island platforms are averaging near 15
mph with gusts over 20 mph. 

.SHORT TERM...Today thru Sunday, 590 to 595 dm falling to near 590
decameter at 500 mb heights will continue across South Florida and
the Keys in association with the aforementioned already anchored
deep middle level ridge(1st paragraph) which will remain in the
same relative position. By Sunday, the heights fall a few
decameters in association with a burgeoning middle and upper 
trough over the NE and Middle Atlantic States, which will 
introduce a little lift and instability next week. Until then, 
available model forecast soundings continue to illustrate lots of 
dry air advecting across the Keys above 850 mb thru the period. 
This lines up with the above mentioned GOES TPW as well. The breezy
to windy conditions, do however, go by the wayside late this 
afternoon and tonight, as surface ridging collapses in advance of 
stationary front. All of these things precipitated the earlier 
forecaster shifts insertion of only dime, 10%, pops in the grids, 
for these periods (today thru Sunday), with thunder removed. The 
only exception is removal of pops during Saturday, likely due to 
the given depth of drier air and light winds, with PWAT below an 
inch for that particular period. Bottom line, it will be mostly 
clear and continued very warm and humid with, very little chance 
for any rain, with lessening breeze.

&&

.LONG TERM...Sunday night thru Thursday, the longwave trough 
along the east coast will drive the frontal boundary over North 
Florida slowly southwards during Sunday. As the surface cold
frontal boundary slows down across South Florida by Monday, 
moisture increases and low level convergence, allowing for 
develoment of showers, and isolated storms as well, given slight 
decrease in stability per upper troughing. So for now we have 
raised pops to low chance, 30% for Monday and Monday night, as 00Z
ECMWF indicates there is still less moisture to deal with in 
advance of this front. Strong high pressure over the Mid-
Mississippi Valley will allow northeast winds to increase with 
breezy to windy conditions as well. 

Then this surface ridge moves quickly to the Southeastern
Seaboard and weakens as our local winds slacken a bit, and become
more east by Tuesday and Tuesday night. Yet weaker ridging 
remains across Central Florida, and is sufficient for gentle to 
moderate flow over the Keys Tues thru Thursday. This will prompt 
isolated chances for showers and storms Tuesday, 20%, thru late 
week(Thursday). High and low temperatures will be near or slightly
above normal.

&&

.MARINE...SCA to continue across for
GMZ033-034-042>044-052>055-072>075 thru at least 15Z, then winds
and seas drop off fairly quick. Will probably have SCEC 
conditions across GMZ033-034-042>044-052>055-072>075 thru the 
early evening, with no headlines or advisories expected thereafter
until Sunday night, when intensifying high pressure will result 
in at least SCEC for GMZ033-034-042>044-052>055-072>075, with SCEC
likely for Monday and Monday night, before winds and seas let 
down again. 

&&

.AVIATION...
Until 00z/19th, VFR conditions can be expected at the Key West 
and Marathon terminals with mostly east winds of 10 to 15 knots 
with gusts near 20 knots can be expected.

&&

.CLIMATE...
In 2009, the daily record low temperature of 65 degrees was recorded 
in Key West. Temperature records have been kept since 1872.

&&

.PRELIMINARY POINT TEMPS/POPS...
Key West  88  80  87  78 / 10 10 -  10 
Marathon  88  80  87  77 / 10 10 -  10 

&&

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...Small Craft Advisory until 11 AM EDT this morning for GMZ033-034-
     042>044-052>055-072>075.

&&

$$

Public/Marine/Fire...Futterman
Aviation/Nowcasts....APA

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