422 
FXUS62 KKEY 060832
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
432 AM EDT Wed Oct 6 2021

.DISCUSSION...
Higher coverage of showers was observed over the Straits of 
Florida compared with early Tuesday morning, matching well 
with GOES16 precipitable water estimates of 1.9 to 2.0 inches
slowly spreading northwest. East winds of 12 to 14 knots were
measured at the reef instrument platforms; also a bit stronger 
than observed Tuesday morning. Temperatures were in the lower
80s, with dewpoints now in the mid 70s.

Water vapor imagery showcased a large, deep cyclonic 
circulation over the mid and lower Mississippi Valley, 
encompassing much of the southeast U.S. as well. A pronounced
dry slot was wrapping around the southern periphery across the
extreme northern Gulf of Mexico and rounding northeast into
Georgia. The upper ridge axis had shifted over the northern
Bahamas, with slow height rises continuing last evening at Key
West. As the upper low lifts northward, the upper ridge will slide
westward and rejoin another cell across northwest Mexico. Warm mid
level temperatures and weak deep lapse rates will likely limit
thunder coverage in spite of the passage of the passage of the
moisture axis, thus chance PoPs continue for the next few days.

Uncertainty grows Friday night and Saturday with the position of
a digging trough axis near or off the southeast U.S. coast, a
downstream impact from a very deep trough axis in the southwestern
U.S. and its downstream ridge alignment across the southern
Plains. Variations continue run to run within respective model
ensembles, with the range from a sharp trough or brief cut-off low
over the Florida Peinsula or displaced to the east. The difference
between likely to categorical rain chances and lower to mid
"chance." At this time there is reasonable agreement in numerical
guidance with the initial forcing Saturday as the trough 
initially digs, with the threat for locally heavy downpours more 
likely with the blend of numerical model solutions favoring the 
eastern, upper Keys. Note that with such weak lower tropospheric
and steering flow for convective cells, the rainfall maxima are
likely to be spotty and determined by boundary collisions from
robust clusters near and over the Florida mainland. 

Later still, how far south the southwest U.S. trough initially 
swings east, then ejects toward the Great Lakes will certainly 
play a strong role in what energy separates from the westerlies 
near the southeast U.S. Early next week may be unsettled, or 
simply significantly drier than the current above-climatology 
rain chances in the public forecast suggests. 

&&

.MARINE...
No watches, warnings, or advisories are in effect for the Florida
Keys coastal waters. From synopsis, high pressure over the 
western north Atlantic and New England will gradually weaken late 
this week. Gentle to occasionally moderate easterly breezes will 
decrease and become light to gentle Friday and continue through 
the weekend. A weak trough of low pressure off the southeast 
United States may extend through the Florida peninsula this 
weekend, increasing the coverage of showers and thunderstorms. 

&&

.AVIATION...
VFR conditions will prevail at both EYW and MTH island terminals 
through Wednesday. Isolated nocturnal shower activity have increased 
in coverage through the night and remain possible through the 
afternoon, uncertainty in timing for decreasing coverage remains 
high. This being said, VCSH has been included through 13z for both 
terminal and details for this afternoon should become more clear by 
daybreak.

&&

.CLIMATE...
In 1873, a major hurricane moving northeast passed about 100 
miles northwest of Key West, where the minimum pressure was 29.28"
and the peak wind gust was 80 mph.

&&

.PRELIMINARY POINT TEMPS/POPS...
Key West  88  80  89  80 / 30 30 40 30 
Marathon  89  80  89  80 / 30 30 40 30 

&&

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...None.
&&

$$

Public/Marine/Fire...JR
Aviation/Nowcasts....Williams

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