Area Forecast Discussion
Issued by NWS Miami, FL

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FXUS62 KMFL 060103 AAB
AFDMFL

Area Forecast Discussion...UPDATED
National Weather Service Miami FL
803 PM EST Fri Mar 5 2021

...A Few Severe Storms Possible Southern Areas Of South Florida
Saturday Afternoon...

...Localized Heavy Rain Potential Saturday Into Saturday Evening
Especially East Coast Metro Areas...

.UPDATE...
A mid to upper level low over the Southern Gulf coast states will
continue to move southeast towards South Florida tonight before
moving across the region on Saturday evening. This will allow for
a weak surface low to develop over the Eastern Gulf of Mexico and
move across South Florida Saturday evening, and allow for a warm
front to develop over the Florida Keys and move northward into
South Florida before stalling over the Alligator Alley.

With the warm front stalling over the Alligator Alley, deeper
moisture should work northward into the southern areas of South
Florida on Saturday leading to the possibility of thunderstorms
in these areas, with locally heavy rain possible over northern
areas. If later short range models forecast the surface low and
warm front to be further northward than currently forecast, then
the threat of thunder could increase for the northern areas of
South Florida.

There is also the possibility of strong to even a few severe
storms mainly over the southern areas on Saturday due to a low to
mid level jet of 30 to 50 knots, a short wave moving through the
mid to upper level of the atmosphere from the Gulf of Mexico, and
colder air around -10 to -13 degrees aloft. The winds will also
be turning with height over South Florida on Saturday ahead of the
weak surface and mid to upper level lows. Therefore, the primary
threats from the thunderstorms will be gusty winds, small hail,
heavy rainfall, and even a possibility of a weak tornado.

Once the mid to upper level low moves east along with the surface
low, the winds will become more northerly as the associated cold
front moves across South Florida. However, the winds over the east
coast metro areas could remain more northeast through the evening
hours of Saturday allowing for a possible coastal trough to set
up. This could help to set up a convergence boundary allowing for
heavy rains to set up along the east coast metro areas. So will
keep the POPs in the scattered to numerous range for Saturday
evening over the east coast metro areas before tapering it down
through the overnight hours. The rest of South Florida will see a
decrease in POPs through Saturday night.

&&

.AVIATION...
The winds will remain light from the east tonight before increasing
to around 10 knots on Saturday. The weather will remain dry tonight
into Saturday morning for most of the TAF sites except for KAPF taf
site where VCSH will be introduce around 14Z. Rest of the TAF sites
will see VCSH from 18Z onward, except for KOPF, KMIA, and KTMB where
a prob 30 group will be introduce from 19Z until 23Z for thunderstorms.
The ceiling and vis will also remain in VFR conditions but could fall
down into MVFR or even IFR conditions with the passage of the showers
and storms after 17Z Saturday.

&&

.PREV DISCUSSION... (Issued 343 PM EST Fri Mar 5 2021)

..Localized Heavy Rain Potential East Coast Saturday and
Saturday Night...

SHORT TERM...

A ridge of high pressure remains established over South Florida
today as a decaying surface trough over the Northwestern Bahamas
continues to gradually dissipate. This should keep any showers that
do develop over the Atlantic waters. A dry airmass remains in place
for South Florida today with a PWAT value of 0.57 inches recorded
during this morning`s 12Z MFL upper air sounding. Winds will become
ENE this afternoon, with dry conditions prevailing across South
Florida.

A cold front is currently moving into northern portions of the
Florida Peninsula today. As a developing low pressure system will be
dropping out of the Plains. This low will move southeastward into
the Gulf of Mexico by early Saturday morning before moving across
the Florida Peninsula. The combination of the approaching low
pressure system and the cold front progressing southwards will allow
for ample moisture and warm air advection to work into the region
during the afternoon/evening hours on Saturday. The chances of
showers and isolated thunderstorms will slowly increase during the
early morning hours of Saturday. According to model guidance, PWATs
of 1.2-1.5 are expected to advect into the region by Saturday. The
increasing moisture at the surface and mid-levels will lead to
widespread showers and isolated embedded thunderstorms across South
Florida. There looks to be some scattered development out ahead of
the main line along the east coast in the late morning hours before
the bulk of the convection associated with the front moves through
the area in the afternoon.

While the bulk of dynamic support will remain mostly north across
Central Florida and Atlantic waters there will be some support of
more organized convection across South Florida. Southwesterly winds
in the mid levels courtesy of a dip in the subtropical jet and
southeasterly winds at the surface ahead of the approaching boundary
over the east coast. Model soundings depict Bulk Shear values in
excess of 50-60kts and 0-1km SRH values of over 100 m2/s2 across the
northern portions of our CWA near the Lake Okeechobee and Palm Beach
region in the afternoon. Lapse rates will be near 6C/km with 500mb
cooling to near -14C. The limiting factor for the development of
stronger storms will be the lack of instability with a lack of CAPE,
depicting less than 100 J/Kg of CAPE across South Florida.

Given the dynamical set-up the greatest area of concern will be over
northern portions of the CWA and the east coast metro and coastal
areas. The aforementioned increased moisture and wind profile may
allow for coastal convergence and potential increased heavy rainfall
along the coast. Rainfall amounts of 1 to 2 inches with the
potential for locally higher amounts. This may lead to very
localized flooding potential where highly efficient rain processes
and multiple rounds of rainfall over the same location will be
possible.

Given the SRH and shear values but lack of instability the remaining
impacts/hazards are highly uncertain but the not out of the realm of
possibilities if a thunderstorm can get going in a low buoyancy high
shear environment. Gusty winds will be possible with any
thunderstorms that may be able to form. Taking a look at hodographs
there is a non-zero threat of funnel clouds or an isolated tornado
tomorrow over northern portions of the region, where the better
dynamics will be located.

LONG TERM...

Saturday Night through Sunday Night...

A mid-level shortwave initially over the Florida Straits will eject
into the Bahamas by Sunday afternoon while phasing with broader
troughing along the Eastern Seaboard. Differential cyclonic
vorticity advection in tandem with jet-level divergence associated
with the passing wave should provide for a broad zone of lower
tropospheric ascent with an area of lower pressures evolving from
the southeast Gulf of Mexico towards the central Bahamas. An
associated weak frontal zone is forecast to locate in the vicinity
of far southern Mainland Florida or the Keys Saturday evening before
departing the area later on Sunday.

At least scattered convection should be ongoing Saturday evening
across the area as the frontal zone locates nearby with weak above-
surface warm advection and an onshore wind component evolving. While
moisture profiles aren`t overly exciting on the broad scale
(precipitable water values ~1.2-1.4 inches) the onshore flow
juxtaposed with a front in the vicinity are signals for coastal
convergence potential and locally heavy rainfall along the east
coast. This is well discussed in the short term forecast above
and the same thinking prevails with regards to localized flooding
potential for the east coast into Saturday evening. Any potential
will be driven by mesoscale details which should become clearer
with time tomorrow so keep up with forecast updates.

Given shear profiles couldn`t rule out a few stronger wind gusts if
any taller convective cores are able to get going, however given
very limited instability this appears to be a very conditional risk
which should be waning with time into Saturday evening.

Slightly cooler temperatures are expected on Sunday after the
frontal passage with breezy northerly winds (possibly turning more
NNE along the east coast) providing for hazardous beach and marine
conditions. The better cold-air advection reaches the area by Sunday
evening with lows dropping to around 50 west of Lake Okeechobee.
Elsewhere look for mostly upper 50s to lower 60s due to the
increasing onshore wind component keeping readings a bit milder for
the Southern Everglades and East Coast Metro Areas.

Monday through Friday...

Ridging aloft should prevail for much of the extended forecast
period as surface high pressure migrates from the Southeast US into
the Atlantic waters. A robust pressure gradient will keep breezy
conditions in place with hazardous marine and beach conditions
prevailing. Otherwise chances for light rain or sprinkles may
intermittently manifest as pockets of shallow moisture push across
the Atlantic waters and east coast metro areas, but any impacts
should be quite minimal. Temperatures should remain seasonal
while gradually warming with time. Given the brisk onshore winds
temperatures will remain warmest from west to east for afternoon
highs with the warmest low temperatures found along the eastern
Beaches.

AVIATION(18Z TAFS)...

Winds continue to veer to the northeast, becoming ENE this
afternoon. Except for KAPF, hi-res models still depict a weak gulf
breeze this afternoon. L/v winds overnight. A cold front
approaches the region tomorrow with southeasterly winds and
increased rain chances with VCSH included for all sites. There is
a chance for thunderstorms but confidence of which terminals and
timing is too low to include at this time.

MARINE...

Winds and seas will continue to subside today as the pressure
gradient over the area waters decreases as a ridge of high pressure
continues to remain established over the area. As a cold front
approaches the region tomorrow, hazardous marine conditions and
unsettled weather will be possible over area waters. In shower and
thunderstorm activity, there is the potential for locally hazardous
marine conditions including gusty winds and a limited potential for
isolated waterspouts. Behind the frontal passage, elevated winds in
the wake of the front will keep seas elevated for the remainder of
the weekend into next week with a northeast swell building across
the Atlantic waters.

FIRE WEATHER...

Dry air and lower dewpoints courtesy of a ridge of high pressure
will bring elevated fire conditions today. Minimum RH values will be
in 20s this afternoon across the gulf coast and western interior
areas. Shower and thunderstorm chances increase on Saturday as a
front approaches from the north. Dry conditions are once again
expected on Sunday as high pressure builds behind the frontal
passage.

BEACHES...

A high risk of rip currents is currently in effect for Palm Beach
county beaches. A moderate risk of rip currents is in effect for
Broward and Miami Dade county beaches today. The elevated risk of
rip currents for Atlantic beaches will continue through the weekend
and into next week. High surf is possible for the Palm Beaches by
early next week with coastal erosion a potential concern.

&&

.PRELIMINARY POINT TEMPS/POPS...
Miami            65  79  63  75 /   0  80  70  20
West Kendall     61  80  62  78 /   0  70  60  20
Opa-Locka        62  79  61  75 /   0  80  70  20
Homestead        62  79  61  75 /   0  70  60  20
Fort Lauderdale  66  78  63  75 /   0  80  80  30
N Ft Lauderdale  66  78  63  73 /   0  90  80  20
Pembroke Pines   63  79  62  75 /   0  80  70  20
West Palm Beach  64  76  61  73 /   0  80  80  30
Boca Raton       65  78  62  74 /   0  90  80  20
Naples           61  77  58  76 /   0  60  40   0

&&

.MFL WATCHES/WARNINGS/ADVISORIES...
FL...High Rip Current Risk through Saturday evening for FLZ168.

AM...None.
GM...None.
&&

$$

Update/Aviation...BNB
Tonight/Saturday and Marine...SPM
Saturday Night through Friday...Hadi

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