954
FXUS62 KKEY 301905
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
305 PM EDT Sat Aug 30 2025

...New AVIATION, PREV MARINE, FORECAST, DISCUSSION...

.AVIATION...
(18Z TAFS)
Issued at 305 PM EDT Sat Aug 30 2025
Prevailing VFR conditions will be observed at both EYW and MTH
for the 18Z TAF period. Near surface winds remain southwesterly
below 10 knots. VCSH or VCTS are included in the TAFs to represent
the chaotic nature of showers and thunderstorms near the
terminals while a cloud line lingers near MTH. Shower coverage is
forecast to peak again this evening. Expect amendments for
detailed VIS and CIG impacts to the terminals.

&&

.DISCUSSION...
Issued at 1010 AM EDT Sat Aug 30 2025
Florida Keys residents woke up to a surprisingly quiet sky to
mark the last weekend of August. Showers and thunderstorms
yesterday dropped almost half an inch of rainfall at the KKEY
office, and the general environmental pattern continues to support
wet days across the Keys. The morning 12Z KKEY sounding sampled
slightly lower heights, which matched GOES-East observations of
troughing across the eastern United States. Two features in the
sounding further support the lack of active convection. First, the
atmosphere dried out above 550 mb, which would inhibit shower
depth later tonight. Second, an inversion was sampled just above
the boundary layer. Thus, despite the morning lull in convection,
the radar is expected to become busy this afternoon once the
surface inversion mixes out. The synoptic features that have
supported the last few days of showers and thunderstorms, such as
a quasistationary front over North Florida, a weak trough along
the Florida Peninsula, and the deepening longwave trough across
the eastern United States, are still in place. No changes proposed
to the inherited package. Those in the Keys should brace for
another round of afternoon to evening thunderstorms.

&&

.MARINE...
Issued at 1010 AM EDT Sat Aug 30 2025
There are no watches, warnings, or advisories in effect for the
Florida Keys coastal waters. From synopsis, an early season
Canadian high pressure system will continue to traverse across the
eastern United States and move into the Atlantic over the next
few days. This will allow for breezes to remain light through the
weekend. Pressure gradient across the Gulf including Florida and
the Florida Keys will increase early next week, resulting in
freshening breezes. Moisture will increase as well, supporting
higher shower and thunderstorm coverage through early next week.

&&

.PREV DISCUSSION...
Issued at 1010 AM EDT Sat Aug 30 2025
Florida Keys residents woke up to a surprisingly quiet sky to
mark the last weekend of August. Showers and thunderstorms
yesterday dropped almost half an inch of rainfall at the KKEY
office, and the general environmental pattern continues to support
wet days across the Keys. The morning 12Z KKEY sounding sampled
slightly lower heights, which matched GOES-East observations of
troughing across the eastern United States. Two features in the
sounding further support the lack of active convection. First, the
atmosphere dried out above 550 mb, which would inhibit shower
depth later tonight. Second, an inversion was sampled just above
the boundary layer. Thus, despite the morning lull in convection,
the radar is expected to become busy this afternoon once the
surface inversion mixes out. The synoptic features that have
supported the last few days of showers and thunderstorms, such as
a quasistationary front over North Florida, a weak trough along
the Florida Peninsula, and the deepening longwave trough across
the eastern United States, are still in place. No changes proposed
to the inherited package. Those in the Keys should brace for
another round of afternoon to evening thunderstorms.

&&

.PREVIOUS FORECAST...
Issued at 341 AM EDT Fri Aug 29 2025
BLUF: The forecast remains riddled with high uncertainty due to an
usual, early season weather system.

A large, complex upper level low is parked across the eastern
half of the U.S. and Canada. The associated trough digs as far
south as the Florida Panhandle. Upstream of this large system is a
broad high pressure moving across northern Canada. As this high
moves east southeast over the coming days it will set up what`s
called a Rex Block, something we don`t see in the summer! Let`s
discuss. As the high moves into eastern Canada, it will push one
portion of the upper level low to the east. However, at the base
of the trough will be a potent shortwave that will become trapped
and eventually develop in a closed, cut-off upper level low. The
high will then sit poleward of this newly formed low, creating the
Rex Block. Given that this is an usual occurence this time of the
year, the Rex Block will be short lived as the flow tries to
immediately return to a more progressive nature.

When this occurs, the cut-off upper level will absorbed the
numerous shortwaves that are initially backed up by the Rex
Block. This will allow the low to sit in place and expand.
Finally, a new large upper level low/trough will dive southeast
out of Canada and merge with the aforementioned trough. This will
lead to a prolonged period of troughiness for the eastern half of
the U.S.

Ok, so what does this mean for the Florida Keys? Depending on how
this intricate dance of physics plays out will ultimately
determine how active of a weather pattern we can expect locally.
This is where most of the uncertainly lies. If the trough is
allowed to expand more equatorward, it will place the base closer
to the Keys, allowing for some upper level support. At the same
time, depending on how far south the trough makes it, will also
determine the placement of a low level ridge that is currently
pivoting northward from the western Caribbean. Lastly, the
placement of a quasi-stalled frontal boundary will be the final
key piece. It currently resides across northern Florida but will
shift south depending on the other factors listed above.

The GFS is more "optimistic" in keeping the trough just far enough
north that the low level ridge is allowed to settle across Cuba.
This would place the Florida Keys in generally a west-southwest to
at times northwest flow. This in turn would not be very favorable
for rain chances. The ECMWF on the other hand is more "pessimistic"
in that it pushes the trough far enough south that the ridge is
not allowed to move up from the Caribbean. This would place us in
a convergence zone of not only some (not great) upper level
support but moisture that will continue to pool across the Keys.
As a result, a more active, wetter period would be expected.

For now, will maintain a middle of the road approach with
rain/thunder chances slightly above normal. There will be days
that ultimately may be wetter or drier than some, but where and
when that may occur too uncertain at this time. Given the lack of
appreciable synoptic flow, our rain chances in the short term will
be heavily dependent on mesoscale forces.

&&

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

$$

Public/Marine/Fire...AJP
Aviation/Nowcasts....AJP
Data Acquisition.....DP

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