Special Weather Statement, NWS Miami, FL

Area Forecast Discussion
National Weather Service Miami FL
344 PM EDT Mon May 18 2020

...Strong to severe storms this afternoon/early evening...
...Another round possible overnight in Southwest Florida...

.Short Term (Rest of Today and Tonight)...

Tropical Storm Arthur is currently moving over the outer banks of
North Carolina and it will continue to move northeastward off of
the Mid-Atlantic coastline through the rest of the afternoon and
evening hours. At the same time, the tail of Arthur, basically a
trough of low pressure will extend into the southeastern portion
of the country. This also combined with a mid to upper level area
of low pressure moving into the Tennessee Valley and a trough of
low pressure moving into the eastern Gulf of Mexico will allow for
a south southwesterly flow to continue across South Florida. The
Gulf coast sea breeze will be allowed to push inland as the east
coast sea breeze will remain pushed up against the coast. All of
this will result in the development of scattered to numerous
showers and thunderstorms especially over the east coast and the
Lake Okeechobee region. Some of these thunderstorms could be
strong to severe this afternoon and this evening as 500mb temps
will be between -9 and -11C across the region along with steep
lapse rates and high MLCAPE over the area. The primary impacts
with these storms will be heavy rainfall, frequent lightning
strikes, small hail, and gusty winds. The potential for some minor
street flooding is possible as well across the east coast with
the heavy rainfall from thunderstorms.

The trough of low pressure over the eastern Gulf of Mexico will
slowly move across the region and into the Atlantic waters later
this evening and into the overnight hours. This will help to keep
the chances of showers and thunderstorms around during this time
frame. The greatest chances of showers and thunderstorms will
continue to be across the east coast as well as the Lake Okeechobee
region.

.Long Term (Tuesday through Sunday)...

The mid-level trough will push into the Gulf waters late tonight
into early Tuesday morning likely spurring additional convection.
Portions of Southwest Florida could see vigorous showers and
thunderstorms overnight spurred by the mid and upper level support
provided by the trough moving through with activity pushing
eastward through the morning. The afternoon focus will remain
along the east coast where the sea breeze, the surface boundary,
and remnant moisture could interact to produce some convection.

The mid-level low will emerge over the Tennessee River Valley late
Tuesday into Wednesday. The surface boundary and associated moisture
should slip to the southeast of the area which may allow a brief dry
slot for portions of the area to emerge. Any dryness should be short-
lived as the mid-level low pulls back northward with the moisture
returning in time for the sea breeze convection to potentially
produce thunderstorms with the potential for heavy rain.

The generally unsettled pattern will persist as the rich moisture
remains across the region through the rest of the week. Diurnal
heating and the presence of sea breezes due to a light synoptic flow
should allow mentionable thunderstorm chances most days except for
those brief winds where a dry slot of air could move through
portions of the region. A ridge of high pressure may try to build
over the aloft over the Gulf but it may not be able to cap
convection as much as a stronger high centered closer to the area.
Temperatures will remain warm with upper 80s and 90s on most
afternoons and mid 60s to 70s for minimum temperatures.

&&

.Marine...
Southwesterly flow will continue through the middle of the
week across the Atlantic and Gulf coastal waters. Seas will
generally remain at 3 feet or less across the local waters.
Scattered to numerous showers and thunderstorms will be possible
each day through the end of the week. Winds and waves will be higher
in and around any showers or thunderstorms.

&&

.Prev Discussion... /issued 135 PM EDT Mon May 18 2020/

Aviation...
Mainly VFR conditions will prevail throughout the forecast period.
The exception to this will be in and around any showers or
thunderstorms that develop this afternoon and this evening where
periods of MVFR or even IFR conditions are possible. South to
southwesterly winds will continue through this evening between 10
and 15 knots. Patchy fog development is possible across the
interior sections during the overnight hours.

Prev Discussion... /issued 1121 AM EDT Mon May 18 2020/

Update / Mesoscale Discussion...

Midlevel water vapor loops indicate a well-defined southern-stream
cyclonic-flow perturbation centered over the Middle Gulf waters well
off the Tampa Bay Area coast.  This feature will continue drifting
eastward or even southeastward, as the centroid of its accompanying
cyclonically-curved jet streak still lies upstream of the trough
axis.  As a result, CVA-associated height falls and related DCVA-
enhanced midlevel cooling preceding this shortwave trough will
continue to overspread the NWS Miami County Warning Area through the
day -- with 500-mb temperatures falling to -8C to -10C from
southeast to northwest.

Meanwhile the low-level mass response preceding the wave is favoring
enhanced isentropic ascent and regenerative convection within a
corridor from the east-central Gulf toward areas from Tampa to Fort
Myers.  This activity will progress northeastward to eastward, with
diurnally destabilizing inflow favoring an increasing potential for
robust convection to accompany this activity across Glades and
Hendry Counties toward/across the Lake Okeechobee region from late
morning into early afternoon.  Meanwhile, areas of cloud-thinning
and partial clearing southeastward of this regime toward southeast
Florida will favor strong destabilization by this afternoon.
Concurrently, differential-heating-induced baroclinicity and
solenoidal circulations along the edges of thicker/denser mid/high-
level cloud decks and old outflow accompanying the more pronounced
isentropic-ascent regime, coupled with decaying outflow from
dissipating convection presently ongoing over Biscayne Bay vicinity,
along with some potential for a modest/broad east-coast sea-breeze
circulation to ensue, will favor a marked uptick in robust
convective potential this afternoon across southeast Florida.
Convection will preferentially regenerate into areas of highest
theta-e through the afternoon into the early evening -- i.e.,
southeastward to southward.

Given the extremely moist planetary boundary layer -- associated
with lowest-100-mb mean mixing ratios of 15-16 g/kg -- convective
inhibition will be low amid sufficient low-level ascent -- aided by
the larger-scale synoptic ascent -- to support high confidence in
the aforementioned regenerative convective regime taking place
today.  Moreover, it appears that an elevated mixed layer has
overspread South Florida from the Sierra Madre Mountains of Mexico --
 accompanied by maximum midlevel lapse rates of 7.0-7.5 C/km.
Related enhanced midlevel CAPE density will favor intense parcel
accelerations, offsetting the effects of precipitation loading / dry
entrainment, in support of robust updrafts.  While modest, the
presence of 20-30 kt of effective shear -- accompanying the enhanced
midlevel height gradient peripheral to the shortwave trough -- will
combine with 2000-3000 J/kg of midlevel-instability-enhanced
boundary-layer buoyancy for intense multicell clusters. In addition
to sporadic instances of small hail, these parameters suggest large
hail -- to around quarter size -- may occur especially where
updrafts remain in more separated/discrete phases.  Moreover, the
enhanced downward buoyancy accompanying the EML could favor damaging
wind gusts where more substantial cell interactions take place among
the multicell clusters.  Confidence continues to grow in isolated
severe winds and hail affecting southeast Florida this afternoon --
especially from Downtown Miami / Miami Beach area northward through
coastal/metro Palm Beach County.  The most-likely timing is 1-7PM.
The latest output from the Statistical Severe Risk Assessment
Model (SSCRAM) depicts both conditional and unconditional
probabilities for damaging wind gusts and severe hail across these
coastal and metro areas of South Florida this afternoon, further
increasing confidence in these convective hazards materializing in
the strongest storms that develop. However, earlier scattered
strong thunderstorms may also affect Hendry/Glades Counties
through the Lake Okeechobee region.

In addition to severe hail/wind potential today, there is also a
reasonable-worst case scenario for a slight inland mass flux in the
lowest 1 km AGL to favor effective SRH near 100 m2/s2 in immediate
proximity to the east coast.  Related streamwise-vorticity
enhancements could conditionally favor the potential for convection
to briefly attain supercellular characteristics within 10-15 miles
of the immediate Atlantic coast -- locally boosting the hail/wind
potential, and possibly supporting a brief/weak tornado.  The
enhanced midlevel lapse rates and related parcel accelerations would
also contribute to enhanced vorticity stretching in the low-levels,
and thus there is a reasonable worst-case scenario for brief tornado
with the east-coast-area convective regime.

Finally, given widespread 1.9-2.0-inch precipitable water, enhanced
outflow establishing foci for convective regeneration/training amid
low MLCINH, and anticipated slow multicellular-convection motion,
heavy rain and flooding will be a concern -- especially for the east-
coast metro areas and vicinity.  If training convection were to
become established over areas that experienced several inches of
rain over the past few days, the potential for significant urban
flooding could occur this afternoon.  Such potential would be highly
localized, though antecedent conditions may bolster this risk.

Ultimately, there remains some uncertainty regarding the exact
details of most-likely strong/severe risk, along with a bit of
uncertainty about the maximum magnitude of potential convective
intensity. This is especially the case given the modest large-scale
ascent over the region. However, there is growing confidence in a
severe-thunderstorm and flooding potential for the east coast metro
areas and vicinity, and all interests across South Florida are
encouraged to monitor weather conditions closely today.

&&

.Preliminary Point Temps/PoPs...
West Palm Beach  72  87  72  87 /  40  60  20  60
Fort Lauderdale  75  87  74  86 /  40  60  20  60
Miami            74  88  74  87 /  40  60  20  50
Naples           72  85  73  86 /  60  50  10  20

&&

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

&&

Previous Mesoscale Discussion...Cohen/Weinman
Marine...55/CWC
Aviation...55/CWC
Short Term...55/CWC
Long Term...02/RAG

Hazardous Weather Outlook for South Florida
National Weather Service Miami FL
942 AM EDT Mon May 18 2020

AMZ610-630-650-651-670-671-FLZ063-066>075-168-172>174-GMZ656-657-676-
190145-
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-
942 AM EDT Mon May 18 2020

...STRONG TO POSSIBLE SEVERE STORMS TODAY...
...HEAVY RAINFALL AND LOCALIZED FLOODING POSSIBLE TODAY...

This hazardous weather outlook is for South Florida.

.DAY ONE...TODAY AND TONIGHT

Thunderstorms: Isolated to scattered thunderstorms are possible
across all of South Florida and its waters today, especially for
portions of the interior and east coast metro areas. A few of the
thunderstorms could become strong, to even severe, with gusty winds,
hail, frequent lightning strikes, and heavy rainfall. A weak isolated
tornado is possible across eastern portions of South Florida.

Tornado: A weak isolated tornado may be possible today with the
strong to severe storms, primarily across the east coast of South
Florida.

Wind: The strongest thunderstorms could produce wind gusts up to 60
mph mainly over the east coast metro areas and the local waters.

Hail: The strongest thunderstorms could produce hail up to quarter
size mainly over the east coast metro areas and the adjacent coastal
waters.

Flooding: Heavy rainfall from thunderstorms, and repeated rounds of
showers/storms, can produce flooding in low lying and poorly
drainage areas, especially for the east coast where it has been
raining the past few days.

Waterspouts: There is a slight chance of waterspouts with any
thunderstorms and showers that do develop over the local waters.

Visibility: Patchy fog is possible over most of South Florida
early this morning, with patchy smoke over the southern Everglades
and interior areas of Collier County due to wildfires. Visibilities
in the fog and smoke could fall below half an mile at times.

Temperatures: Heat indices could reach 100 degrees over portions of
the interior and East Coast this afternoon, with greater than 105
degrees over portions of eastern Palm Beach County.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

There will be a chance of thunderstorms across South Florida
throughout the week. Gusty winds, locally heavy rainfall, lightning,
and waterspouts will be possible with the strongest storms.

The threat of rip currents for Atlantic beaches will also increase
towards the end of the work week as winds become more easterly over
South Florida.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed. Please relay any information about
observed severe weather to the NWS while following all local, state,
and CDC guidelines.

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

Fell

Special Weather Statement
National Weather Service Miami FL
242 PM EDT Mon May 18 2020

FLZ071>074-181930-
Inland Broward County FL-Metro Broward County FL-
Metropolitan Miami Dade FL-Inland Miami-Dade County FL-
242 PM EDT Mon May 18 2020

...SIGNIFICANT WEATHER ADVISORY FOR NORTH CENTRAL MIAMI-DADE AND
SOUTHERN BROWARD COUNTIES UNTIL 330 PM EDT...

* At 242 PM EDT, National Weather Service meteorologists were
  tracking a strong thunderstorm near Miccosukee Resort, or 14 miles
  southwest of Miramar, moving northeast at 20 mph.

* Nickel size hail, funnel clouds, and winds in excess of 45 mph
  possible with this storm.

* Locations impacted include...
  Pembroke Pines, Hollywood, Miramar, Davie, Sunrise, Miami Gardens,
  Weston, Miami Lakes, Cooper City, Hialeah Gardens, Medley, Royal
  Palm Ranches, Palm Springs North, Sunshine Acres, Miccosukee
  Resort, Intersection I-75 And Griffin Road, Pennsuco, Intersection
  Krome And U.S. 27 and Country Club.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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.

This activity was also developing in an environment favorable for the
formation of funnel clouds. Stay tuned to NOAA weather radio and
local media for additional updates and possible warnings.

To report severe weather, contact your nearest law enforcement
agency. You can also share your report with NWS Miami on Facebook and
Twitter.

&&

LAT...LON 2573 8053 2588 8069 2613 8038 2604 8021
TIME...MOT...LOC 1842Z 210DEG 18KT 2584 8052

13

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MIAMI FL
301 PM EDT MON MAY 18 2020

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

0230 PM     FLOOD            BOYNTON BEACH           26.53N 80.09W
05/18/2020                   PALM BEACH         FL   BROADCAST MEDIA

            WPTV RETWEETED A VIDEO THAT SHOWS FLOODING
            NEAR THE INTERSECTION OF CONGRESS JUST SOUTH
            OF WOOLBRIGHT IN BOYNTON BEACH. ONE CAR IS
            STALLED ON 30TH AVE, WHILE OTHERS HAVE
            TURNED AROUND ON THAT STREET. (CORRECT:
            LAT/LON 26.4973, -80.0897).

&&

HVN

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MIAMI FL
358 PM EDT MON MAY 18 2020

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

0230 PM     TSTM WND GST     2 W WELLINGTON          26.66N 80.29W
05/18/2020  M46 MPH          PALM BEACH         FL   MESONET

            MESONET STATION FW5300 IN WELLINGTON
            MEASURED A 46 MPH WIND GUST OUT OF THE SE AT
            2:30 PM.

&&

RAG

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MIAMI FL
401 PM EDT MON MAY 18 2020

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

0257 PM     TSTM WND GST     15 W WESTON             26.14N  80.63W
05/18/2020  M48 MPH          BROWARD            FL   MESONET

            THE BROWARD SHERIFF'S OFFICE FIRE RESCUE STATION ON
            ALLIGATOR ALLEY REPORTED A 48 MPH WIND GUST AT 257 PM.

&&

EVENT NUMBER MFL2000075

RAG

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MIAMI FL
410 PM EDT MON MAY 18 2020

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

0356 PM     HEAVY RAIN       2 NNE DELRAY BEACH      26.48N  80.08W
05/18/2020  M7.37 INCH       PALM BEACH         FL   MESONET

            A TOTAL OF 7.37 INCHES OF RAIN MEASURED AS OF 4 PM AT
            WEATHER UNDERGROUND SITE KFLDELRA71 NEAR LAKE IDA IN
            DELRAY BEACH.

0404 PM     HEAVY RAIN       2 NW DELRAY BEACH       26.48N  80.11W
05/18/2020  M5.41 INCH       PALM BEACH         FL   MESONET

            MEASURED RAINFALL OF 5.41 INCHES AT WEATHER UNDERGROUND
            STATION KFLDELRA49 IN THE SABAL LAKES COMMUNITY OF
            DELRAY BEACH.

0407 PM     HEAVY RAIN       2 SSW OCEAN RIDGE       26.50N  80.07W
05/18/2020  M5.43 INCH       PALM BEACH         FL   MESONET

            MEASURED RAINFALL OF 5.43 INCHES AT WEATHER UNDERGROUND
            STATION KFLBOYNT1 NEAR BETHESDA HOSPITAL EAST IN BOYNTON
            BEACH AS OF 4:05 PM.

&&

EVENT NUMBER MFL2000076
EVENT NUMBER MFL2000077
EVENT NUMBER MFL2000078

MOLLEDA

Special Weather Statement
National Weather Service Miami FL
412 PM EDT Mon May 18 2020

FLZ067-068-071>074-168-172-173-182100-
Inland Broward County FL-Coastal Broward County FL-
Coastal Palm Beach County FL-Metro Broward County FL-
Metropolitan Miami Dade FL-Inland Palm Beach County FL-Inland Miami-
Dade County FL-Metro Palm Beach County FL-
Coastal Miami Dade County FL-
412 PM EDT Mon May 18 2020

...SIGNIFICANT WEATHER ADVISORY FOR NORTHERN MIAMI-DADE...BROWARD AND
SOUTHEASTERN PALM BEACH COUNTIES UNTIL 500 PM EDT...

* At 411 PM EDT, National Weather Service meteorologists were
  tracking strong thunderstorms along a line extending from near
  Loxahatchee NWR to Twin Lakes to Broadview Park to near
  Intersection I-75 And Griffin Road to Pennsuco. Movement was east
  at 15 mph.

* Nickel size hail, funnel clouds, and winds in excess of 45 mph
  possible with these storms.

* Locations impacted include...
  Miami, Hialeah, Fort Lauderdale, Pembroke Pines, Hollywood,
  Miramar, Coral Springs, Pompano Beach, Davie, Miami Beach,
  Plantation, Sunrise, Boca Raton, Deerfield Beach, Boynton Beach,
  Delray Beach, Tamarac, Margate, Coral Gables and Lake Worth.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Funnel clouds occasionally touch down and produce tornadoes or
waterspouts. Move indoors and stay away from windows.

To report severe weather, contact your nearest law enforcement
agency. You can also share your report with NWS Miami on Facebook and
Twitter.

&&

LAT...LON 2661 8003 2623 8003 2612 8006 2571 8009
      2584 8083 2617 8075 2614 8055 2633 8041
      2658 8038
TIME...MOT...LOC 2011Z 277DEG 14KT 2650 8018 2620 8016 2609 8023 2603
8039 2590 8041

13