Coastal Flood Statement 1, NWS Key West, FL

Area Forecast Discussion
National Weather Service Key West FL
342 AM EDT Mon Aug 3 2020

.DISCUSSION...
As Tropical Storm Isaias continues to move NNW parallel to the
Florida east coast and further away from the Keys, our area is
left with light winds backing around to the S/SW, along with lines
of light to moderate showers developing at times within weak low
level convergence bands. This shower activity has remained rather
shallow during the night, with no thunderstorms observed. The lack
of deep convection is likely due to continued dryness aloft, as
shown by the 06Z special Key West sounding. Although PW was near
the 75th percentile for the date at 2.03 inches, dewpoint
depressions of 10C to 25C in the 700-500 mb layer are preventing
the showers from developing into thunderstorms. Otherwise, skies
are partly cloudy along the island chain, with temperatures
hovering in the lower to mid 80s and dewpoints in the upper 70s.

For today, model guidance suggests that the mid level dry slot
currently over the Keys will remain in place, while weak low level
flow from the SW to WSW aligns along the island chain. This may
promote cloud line development, although the vertical extent will
be challenged due to the dry air aloft, especially over the Lower
Keys. That said, some of the CAM guidance is hinting at at least
shower development along a cloud line during the day, and will
maintain low to mid chance PoPs of 30 to 40 percent, with highest
rain chances in the Upper Keys where the dry air aloft may be less
of an inhibiting factor.

As Isaias exits into the Carolinas and Mid Atlantic states
tonight and Tuesday, an advancing mid latitude trough dropping
into the Lower Mississippi Valley will help prevent a quick return
of the Atlantic subtropical ridge both at the surface and aloft.
The mid level dry slot is forecast to remain over our area tonight
and Tuesday, which should continue to suppress convection to some
extent. Thereafter, a surge of deep moisture is predicted to
spread into the Keys from the Caribbean on developing SE flow.
This ample moisture combined with light low level flow and the
lack of any suppressing ridge aloft should allow for above normal
PoPs in the 40 to 50 percent range during the midweek period.
Heading into the end of this week and the upcoming weekend,
guidance remains consistent with the subtropical ridge building
back into Florida, bringing considerable drying aloft and
increasing easterly low level flow across the Keys. Have
maintained near climo 30 percent PoPs for those periods.

&&

.MARINE...
Overnight observations show gentle southerly breezes in Florida
Bay and Hawk Channel off the Upper Keys, with light SW breezes
elsewhere. Winds will remain slightly elevated along the Upper
Keys today, but expect nothing more than around 10 knots.
Otherwise, light SW flow will back to S tonight and then settle to
mostly SE Tuesday through Thursday. High pressure building
westward across Florida will bring increasing ESE flow Thursday
night through Friday night, but winds are expected to remain in
the gentle to moderate range with no advisories or cautionary
headlines needed.

&&

.AVIATION...
VFR conditions will prevail at both island terminals. Winds will
be 5 to 10 knots out of the southwest for the majority of the
period and then shift to the south-southeast around 02Z. Due to
the southwesterly winds, there is potential for reverse cloud line
development. This has the potential to bring showers to the MTH
terminal, however, confidence is not high enough to include a VCSH
at this time. Amendments will be made as necessary.

&&

.PRELIMINARY POINT TEMPS/POPS...
Key West  91  83  91  83 / 20 20 30 50
Marathon  92  82  92  82 / 30 20 30 40

&&

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

Public/Marine/Fire...Jacobson
Aviation/Nowcasts....NB
Data Acquisition.....DR

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Hazardous Weather Outlook
National Weather Service Key West FL
522 AM EDT Mon Aug 3 2020

FLZ076>078-GMZ031>035-042>044-052>055-072>075-041000-
Monroe Upper Keys-Monroe Middle Keys-Monroe Lower Keys-
Florida Bay including Barnes Sound, Blackwater Sound, and
Buttonwood Sound-
Bayside and Gulf side from Craig Key to west end of Seven Mile
Bridge-
Gulf waters from East Cape Sable to Chokoloskee 20 to 60 NM out
and beyond 5 fathoms-
Gulf of Mexico including Dry Tortugas and Rebecca Shoal Channel-
Gulf of Mexico from west end of Seven Mile Bridge to Halfmoon
Shoal out to 5 Fathoms-
Hawk Channel from Ocean Reef to Craig Key out to the reef-
Hawk Channel from Craig Key to west end of Seven Mile Bridge out
to the reef-
Hawk Channel from west end of Seven Mile Bridge to Halfmoon Shoal
out to the reef-
Straits of Florida from Ocean Reef to Craig Key out 20 NM-
Straits of Florida from Craig Key to west end of Seven Mile
Bridge out 20 NM-
Straits of Florida from west end of Seven Mile Bridge to south of
Halfmoon Shoal out 20 NM-
Straits of Florida from Halfmoon Shoal to 20 NM west of Dry
Tortugas out 20 NM-
Straits of Florida from Ocean Reef to Craig Key 20 to 60 NM out-
Straits of Florida from Craig Key to west end of Seven Mile
Bridge 20 to 60 NM out-
Straits of Florida from west end of Seven Mile Bridge to south of
Halfmoon Shoal 20 to 60 NM out-
Straits of Florida from Halfmoon Shoal to 20 NM west of Dry
Tortugas 20 to 60 NM out-
522 AM EDT Mon Aug 3 2020

This Hazardous Weather Outlook is for the Florida Keys and
adjacent coastal waters.

.DAY ONE...TODAY AND TONIGHT

Atmospheric conditions will be marginally favorable for
waterspouts today across the nearshore waters of the Florida Keys.
Waterspouts tend to form beneath lines of building cumulus
clouds, just at the hint of rain. Waterspouts can easily flip
boats, and should be avoided always.

Isolated thunderstorms will be possible today and tonight, with
locally gusty winds and lightning being the primary hazards.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

Isolated to scattered thunderstorms will be possible Tuesday
through Sunday, with locally gusty winds and lightning being the
primary hazards.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.