Flood and Damaging Winds in Florida, May 16, 2020

Area Forecast Discussion
National Weather Service Miami FL
212 AM EDT Sat May 16 2020

.Aviation...

Scattered showers will impact mainly the northeastern terminals
(FLL/FXE/PBI) through the morning hours. Periods of heavy rain and
sub-VFR conditions are likely. Otherwise a mix of VFR and MVFR
ceilings should prevail this morning, trending towards VFR this
afternoon. Shower chances should diminish by late morning.

&&

.Prev Discussion... /issued 740 PM EDT Fri May 15 2020/

Aviation...
Scattered to numerous showers will continue tonight especially
across the east coast terminals. There could be periods of MVFR or
even IFR in the heavier showers tonight. Winds will remain out of
the northeast between 10 and 15 knots this evening. Winds will
then shift out of the northwest by tomorrow morning as an area of
low pressure starts to pull away from the area. A chance of
showers cannot be ruled out for tomorrow especially along the east
coast terminals.

Mesoscale Discussion (Valid until 06Z)...

Surface observations and visible satellite imagery continue to
indicate an elongated surface trough of low pressure extending from
off the coast of Miami-Dade County southward through the coastal
waters east of the Upper Keys. Continued latent heating associated
with pulsing convection along the northern periphery of this trough
is expected to support it's northward progression off the coast of
South Florida into the overnight hours. Mesoanalysis fields
highlight this inverted trough embedded within the background
easterly current -- with coastal convergence amid northeasterlies
west of the trough axis enhancing precipitation development over
coastal/metro sections of Miami-Dade and Broward Counties during the
past couple of hours.

Present indications are that the continued northward progression of
the low-level mass field perturbation will foster maintained coastal
convergence over the aforementioned areas into the early evening,
spreading northward toward metro/coastal Palm Beach County later in
the evening into the overnight hours. The potential exists for
nocturnally enhanced outgoing longwave radiation at the top of a
deep moist layer to foster subtle steepening of lapse rates in this
layer through the overnight hours. This factor, combined with the
aforementioned mesoscale convergence, could foster an additional
gradual uptick in east-coast precipitation development during the
next several hours. There is some possibility for modest, gradual
consolidation of the otherwise disorganized trough through tonight.
If this consolidation were to occur, then an axis of confluence /
deformation zone could become apparent along the western periphery
of the evolving trough. This deformation zone would be a focus for
repeated rounds of shower activity, and could extend northward
toward coastal Palm Beach County through the overnight hours.
Ultimately, the overall disorganized character of the low-level mass
field perturbation renders low predictability regarding the details
of the position and geometry of a focused corridor of heavy rainfall
-- extending to its location relative to coastal locations. It is
possible that this focused area of heavy rainfall remains offshore.
However, recent radar loops suggest that this activity could affect
coastal and perhaps metro areas extending northward from northern
Miami-Dade to Broward and Palm Beach Counties overnight.

Given an influx of rich, sub-tropical moisture into the corridor of
enhanced mesoscale convergence near the coast -- characterized by
precipitable water of around 2 inches -- precipitation efficiency
will be substantial. Moreover, forecast soundings indicate warm-
cloud layer depths of around 4.0-4.5 km, associated with deep moist-
neutral lapse rates. This will favor collision-coalescence
precipitation-generation processes, amid a modest convective
component aided by the very moist boundary layer -- e.g., lowest-100-
mb mean mixing ratio around 16 g/kg. This will conditionally support
large, tropical-type rainfall rates, especially into the overnight
hours owing to enhanced nocturnal cooling at the top of the moist
layer.

Whether this conditional potential for heavy rainfall were to
be realized in association with repeated rounds of precipitation is
still uncertain owing to uncertainty in the development of the low-
level troughing off the southeast Florida coast. However, there
is a reasonable worst-case scenario where some locations receive a
few to several inches of rain. Given earlier rainfall totals of a
few to several inches which locally saturated soils, the
potential for enhanced run-off will exist, and a reasonable worst-
case scenario for urban flooding, and even flash flooding, could
extend northward across northern Miami-Dade through Broward and
Palm Beach Counties into the overnight hours. Furthermore, high
tide around the 4AM and 5AM hours could exacerbate the flooding
potential along the immediate coast. However, ultimately, if heavy
rains become established offshore, this threat will be minimized
and/or highly localized tonight. Nevertheless, the risk for
flooding could be increasing over metro/coastal South Florida from
northern Miami-Dade County northward to Palm Beach County.

Prev Discussion... /issued 431 PM EDT Fri May 15 2020/

Short Term (Through Saturday)...

Widespread rain showers and a few thunderstorms will continue to
rotate across the area as a developing area of low pressure tries to
develop over or near the northwestern Bahamas later this evening or
tonight before moving off to the northeast over the Atlantic. The
National Hurricane Center is giving this system a high (80%) chance
of developing into a tropical or sub-tropical storm over the next 2
days. If this system forms, it would be the first of the 2020
Atlantic Tropical Season and given the name Arthur. Either way, the
impacts for us locally will remain the same--windy and rainy. Windy
conditions will continue into the evening due to a combination of a
tight pressure gradient and convection but will slowly begin to
relax some tomorrow as the system moves off to the northeast. That
being said, a Wind Advisory remains in effect for the Atlantic
coastline until tomorrow morning. While PoPs have trended downward
slightly for tomorrow as it appears South Florida may be more on
the "dry" side of the developing system, scattered rain showers
can be still be expected across the east coast and Lake region.

Long Term (Sunday through Friday)...

As a tropical or subtropical system moves northeastward from the
northwestern Bahamas across the western Atlantic waters, steering
flow will transition to a southwesterly direction across South
Florida. This may allow for drier air to advect across South
Florida from the southeastern Gulf of Mexico, briefly reducing
rain chances across the area. A few diurnally driven rain showers
will still be possible on Sunday, especially across inland and
eastern portions South Florida.

By Monday into Tuesday, deterministic model solutions depict a major
shortwave trough digging into the southeastern CONUS and eventually
even into the Gulf of Mexico. Height falls associated with this
feature are evident in NWP ensemble output across the eastern Gulf
of Mexico as well as South Florida, suggesting the potential for
stronger mid/upper-level forcing for ascent to materialize across
the region by mid-week. As the shortwave trough amplifies, a
poleward mass flux may facilitate the advection of deeper moisture
across South Florida, further increasing the chances of greater
convective coverage. This evolution of the synoptic pattern would
bring high rain chances across South Florida through the extended
period with increasing thunderstorm chances and localized heavy
rainfall also quite possible. Please keep up with the latest
forecast information as large differences exist amongst the
deterministic global model solutions in the extended period.

Marine...

A Gale Warning continues for the Atlantic waters and Biscayne Bay
until 8 AM tomorrow. A Small Craft Advisory is in effect elsewhere
until 8 PM. Rain showers and a few thunderstorms will remain
possible across the waters through tomorrow as a developing area of
low pressure forms near the northwest Bahamas and moves off to the
northeast. Gusty winds, lightning, and waterspouts will be possible
with this activity. Winds will gradually become more northwesterly
into tomorrow as the system moves northeastward. Marine conditions
my improve late weekend into early next week.

Beach Forecast...

A High Risk of Rip Currents is in effect for the Atlantic beaches
through tomorrow morning due to breezy onshore flow. A High Surf
Advisory is also in effect for Palm Beach and Broward county beaches
through this evening.
&&

.Preliminary Point Temps/PoPs...
West Palm Beach  84  71  87  71 /  40  10  20  10
Fort Lauderdale  86  73  86  73 /  30  10  20  10
Miami            86  72  87  73 /  20  10  20  10
Naples           85  71  86  71 /  10  10  10   0

&&

.MFL WATCHES/WARNINGS/ADVISORIES...
FL...High Rip Current Risk until 8 AM EDT this morning for FLZ168-172-
     173.

     Wind Advisory until 8 AM EDT this morning for FLZ168-172-173.

AM...Gale Warning until 8 AM EDT this morning for AMZ630-650-651-670-
     671.

GM...None.
&&

Marine...32/MM/18/Weinman
Aviation...34/SPM
Beach Forecast...32/MM
Short Term...32/MM/18/Weinman
Long Term...18/Weinman

Hazardous Weather Outlook for South Florida
National Weather Service Miami FL
452 PM EDT Fri May 15 2020

AMZ610-630-650-651-670-671-FLZ063-066>075-168-172>174-GMZ656-657-676-
160900-
Lake Okeechobee-Biscayne Bay-
Coastal waters from Jupiter Inlet to Deerfield Beach FL out 20 NM-
Coastal waters from Deerfield Beach to Ocean Reef FL out 20 NM-
Waters from Jupiter Inlet to Deerfield Beach FL from 20 to 60 NM-
Waters from Deerfield Beach to Ocean Reef FL from 20 to 60 NM
excluding the territorial waters of Bahamas-Glades-Hendry-
Inland Palm Beach-Metro Palm Beach-Coastal Collier-Inland Collier-
Inland Broward-Metro Broward-Inland Miami-Dade-Metro Miami-Dade-
Mainland Monroe-Coastal Palm Beach-Coastal Broward-Coastal Miami-
Dade-Far South Miami-Dade-
Coastal waters from Chokoloskee to Bonita Beach FL out 20 NM-
Coastal waters from East Cape Sable to Chokoloskee FL out 20 NM-
Waters from Chokoloskee to Bonita Beach FL from 20 to 60 NM-
452 PM EDT Fri May 15 2020

...Heavy Rainfall Possible East Coast...
...Gale Warning in Effect for Atlantic Waters...

This hazardous weather outlook is for South Florida.

.DAY ONE...TONIGHT

Heavy Rainfall: Locally heavy rainfall will be possible across the
East Coast metros tonight. Flooding of streets and low lying areas
will be possible.

Thunderstorms: Rain and a few thunderstorms will remain possible
across South Florida tonight. Gusty winds, heavy rainfall, funnel
clouds and lightning will be possible.

Waterspouts: Waterspouts are possible across the local waters as
showers and storms move across the region.

Rip Currents: There is a high risk of rip currents for the Atlantic
Beaches.

Wind: Easterly winds around 20 to 30 knots with higher gusts across
the coastal waters. A Gale Warning is in effect for the Atlantic
and Biscayne Bay waters due to frequent wind gusts above 34 knots
A Small Craft Advisory is in effect for the remainder of the
coastal waters. A Wind Advisory is also in effect for the immediate
Atlantic Coast for wind gusts equal to or exceeding 35 mph.

Waves: Seas 7 to 9 feet, with occasional seas to 11 feet, in/near the
Gulf Stream.

Surf: A High Surf Advisory is in effect for coastal Palm Beach and
Broward Counties due to large breaking waves of 6 to 7 feet. Some
minor beach erosion is possible.

Visibility: Areas of smoke due to a wildfire across portions of
western Collier County. Visibility may be affected at times.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

Hazardous marine and beach conditions will be possible through early
Saturday before gradually improving this weekend.

There will still be a chance of thunderstorms on Saturday, and then
they will increase once again on Tuesday and through the rest of the
week. Gusty winds, locally heavy rainfall, lightning, and waterspouts
will be possible with the strongest storms.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed. Please report any flooding or other
damage to the National Weather Service in Miami if you can do so
safely and while following all local and state guidelines on social
distancing.

For more information...visit the National Weather Service in
Miami website at www.weather.gov/miami.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MIAMI FL
944 PM EDT FRI MAY 15 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0850 PM     FLASH FLOOD      LAUDERHILL              26.15N  80.21W
05/15/2020                   BROWARD            FL   NWS EMPLOYEE

            AN OFF-DUTY NWS METEOROLOGIST REPORTED SIGNIFICANT
            STEET FLOODING SEVERAL INCHES DEEP AT THE INTERSECTION
            OF NW 47TH AVE AND NW 21ST ST AND VICINITY IN
            LAUDERHILL, FL. FLOOD WATERS ACCUMULATED WITH HEAVY
            RAINS EXTENDING THROUGH THE 8PM HOUR. THEREAFTER,
            FLOODING PERSISTED WITH LIGHT RAIN CONTINUING TO BE
            REPORTED.

&&

EVENT NUMBER MFL2000057

WEINMAN