Special Weather Statement, NWS Miami, FL

Area Forecast Discussion
National Weather Service Miami FL
344 PM EDT Tue Jun 15 2021

...Localized/Urban Flooding Possible for Metropolitan Locations...
...A Few Strong Thunderstorms Possible Today...

.SHORT TERM...

Through Wednesday

A 500 hPa short-wave trough remains oriented NE/SW through central
Florida and into the NE Gulf of Mexico. This will maintain a fairly
active weather pattern across South Florida through this afternoon
and into the evening. Though today's convective activity may not be
as synoptically driven and as widespread as yesterday, scattered
thunderstorms are forecast to occur primarily across metropolitan
regions this afternoon. The 12Z MFL sounding revealed an environment
with effective bulk shear values around 15-20 kt, storm relative
helicities of near 100 m^2/s^2, and 500 hPa temperatures around -8C.
Sufficient forcing should be realized in the form of sea-breeze
circulations and other mesoscale differential heating boundaries,
and therefore these parameters may support a few loosely organized
stronger storms with more robust updrafts capable of producing
strong wind gusts and small hail. The primary threat for today
however will be localized and urban flooding for poorly drained and
recently soaked metropolitan regions, primarily over populated
portions of Miami-Dade, Broward, and Palm Beach Counties. The KEY
12Z sounding revealed low level south/southwesterly winds, which may
act to deepen the moist layer region-wide by advecting higher theta-
e values northward and possibly also providing a slight augmentation
to the low-level wind shear profile. This will be something to
monitor going forward for this afternoon and may support a few wet
microbursts and increased localized flooding potential.

By tomorrow, short-wave troughing becomes more diffuse as the larger-
scale trough axis becomes displaced towards the northeast. As this
process occurs, a noticeable subtropical jet stream materializes
over the eastern Gulf of Mexico around 27N latitude. Upper level
diffluent streamlines and corresponding mass divergence looks as
though it will materialize across the region, while low level
south/southeasterly flow will maintain impressive moisture
advection across the region. Hazards will remain similar to today,
although increasing cloud cover may reduce CAPE values while an
enhancement of the bulk shear profiles may be realized due to
enhanced veering low-level flow. Therefore a conditional threat
for a few stronger and perhaps marginally severe storms may exist
for tomorrow. The ongoing flooding threat will also persist for
portions of the east coast metropolitan region, and the most
vulnerable areas will be recently soaked and/or urban regions.

Temperatures will be warm and humid today, with maximum temperatures
in the lower 90s across most of the region, though it will feel much
warmer owing to dewpoints in the mid 70s. Tomorrow will be slightly
cooler due to increased cloud cover associated with synoptic scale
lift, as well as physical cooling processes associated with more
widespread rain.

.LONG TERM...

No meaningful changes to the long term forecast and the previous
discussion is included below.

PREV DISCUSSION... (Issued 301 AM EDT Tue Jun 15 2021)

Long term (Wednesday Night through Monday):

Models continue to depict a mid/upper trough lingering over the
area through Thursday, while the sfc ridge over the west Atlantic
remains just to our east. This will keep generally SE flow across
SoFlo for the beginning of the long term, with moisture advection
keeping elevated PWATs across the southern half of the peninsula.
Model soundings depict up to 2 inch PWAts on Thursday.

The dominant SE flow will again push the best POps over the
interior. Highest POps remain over those areas, along with
increasing chances for strong thunderstorms during the afternoon and
evening hours. Repeated bouts of showers over the same locations
may result in localized flooding on Thursday.

Long range models show reasonable agreement in weakening the trough
and expanding the Atlantic ridge towards the state by Friday. In
addition, another Saharan Air Layer event may also reach the area in
the Fri-Sat timeframe. These features will combine to bring a drop
in POPs, down to around 20-25 percent by Friday afternoon, and
into Saturday. For Sun, model solutions suggest the potential for
an area of disturbed weather to develop over the west Gulf, which
could modify the airmass with increasing moisture for the rest of
the weekend. But uncertainty with this feature remains in the
models, so its potential role in our forecast for the weekend
remains unclear. Interests in the upcoming weekend forecast should
continue to monitor the updates to the official forecast.

&&

.AVIATION(18Z TAFS)...

Showers/storms converging on the east coast metro areas now
through late afternoon. Impacts likely for most of the terminals,
with periods of sub-VFR and gusty winds. Shower chances should
diminish somewhat later tonight with storm chances returning
tomorrow.

&&

.MARINE...

Scattered to numerous showers/thunderstorms  are forecast to develop
across the local waters of South Florida primarily through this
afternoon and evening. Outflows from any developing storms may
produce locally enhanced wind gusts and elevated seas, as well as
frequent lightning and small hail. Waterspouts will be possible
across all local waters as well, especially within any stronger
thunderstorms that develop. These hazards appear to continue through
at least Wednesday as favorable conditions for thunderstorms
linger over the region.

&&

.BEACHES...

An enhanced rip current risk exists for portions of coastal Collier
County. This may persist through the middle part of the week as
southwesterly flow continues over parts of this region.

&&

.PRELIMINARY POINT TEMPS/POPS...
Miami            78  88  77  88 /  40  70  50  60
West Kendall     76  89  75  89 /  40  70  50  60
Opa-Locka        76  88  75  89 /  40  70  50  60
Homestead        76  87  75  87 /  30  70  50  60
Fort Lauderdale  77  88  77  88 /  30  70  50  60
N Ft Lauderdale  77  86  77  86 /  30  70  50  60
Pembroke Pines   76  87  75  88 /  40  70  50  60
West Palm Beach  75  87  74  86 /  30  70  50  60
Boca Raton       77  89  76  87 /  30  70  50  60
Naples           77  87  74  88 /  40  70  60  70

&&

.MFL WATCHES/WARNINGS/ADVISORIES...
FL...None.
AM...None.
GM...None.
&&

Tonight/Wednesday and Aviation/Marine...SRB
Wednesday Night through Tuesday...AR

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Special Weather Statement
National Weather Service Miami FL
500 PM EDT Tue Jun 15 2021

FLZ069-070-152145-
Coastal Collier County FL-Inland Collier County FL-
500 PM EDT Tue Jun 15 2021

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN COLLIER COUNTY UNTIL
545 PM EDT...

* At 500 PM EDT, National Weather Service meteorologists were
  tracking a strong thunderstorm 8 miles east of Cape Romano, or 9
  miles west of Everglades City, moving northeast at 15 mph.

* Winds in excess of 45 mph and excessive cloud-to-ground lightning
  possible with this storm.

* Locations impacted include...
  Everglades City, Carnestown, Royal Palm Hammock, Copeland, South
  Blocks Golde, Cape Romano Aquatic Preserve, Fakahatchee Strand
  State Preserve and Port Of The Island.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

These winds can down small tree limbs and branches, and blow around
unsecured small objects. Seek shelter in a safe building until the
storm passes.

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm. If
you can hear thunder, you are close enough to be struck! Seek a safe
shelter inside a building or vehicle.

If on or near the water, move indoors or inside a vehicle. If you can
hear thunder, you are close enough to be struck by lightning. Move to
safe shelter now! Do not be caught on the water in a thunderstorm.

&&

LAT...LON 2609 8161 2597 8127 2579 8144 2579 8146
      2577 8153 2581 8161 2580 8162 2583 8166
TIME...MOT...LOC 2100Z 216DEG 12KT 2584 8154

Hadi/RAG