Special Weather Statement, NWS Miami, FL

Area Forecast Discussion
National Weather Service Miami FL
258 PM EDT Sun Jul 5 2020

.Short Term...

Rest Of This Afternoon (Mesoscale Update)...

Visible satellite loops indicate more widespread boundary-layer
cumulus development across South Florida today compared to
yesterday -- indicative of greater tropospheric moisture content
responding to mass fluxes along the periphery of a northern Gulf
cyclonic-flow perturbation. As a result, convective coverage
today should be greater today than yesterday -- more scattered to
numerous today. Precipitable water has increased by around 0.2
inch during the past day, which will increase the conditional
potential for precipitation loading to strengthen downdrafts,
while midlevel lapse rates remain at a similar 6.0-6.5 C/km.
Midlevel winds today are west-southwesterly around 15 kt -- about
5 kt weaker than those yesterday. Given the marginal decrease in
already modest vertical shear, though still locally enhanced along
and east of the east-coast sea-breeze boundary that has edged
inland, the boosted tropospheric moisture should still maintain a
microburst potential with convection maturing and advancing
toward the east coast in through 7PM. Lateral expansion of
related strong-wind potential could accompany cold-pool
amalgamation toward the east-coast vicinity after around 4PM. An
isolated damaging wind gust could occur as a reasonable worst-
case scenario, especially where low-level lapse rates steepen the
most from metro/coastal Broward into metro/coastal Palm Beach
County. Also, isolated hail -- mostly small -- could accompany
incipient updraft stages. Though, sufficiently cool midlevel
profiles could support an isolated risk for quarter-size hail.
Frequent lightning and torrential downpours are expected, and
backbuilding convection could yield a localized-flooding risk.

Overnight and Monday...

Overnight tonight temperatures will drop into the mid 70s over the
interior with upper 70s along the gulf coast and near to low 80s over
the east coast metro. Showers and thunderstorms will be possible
over the Gulf and Atlantic waters overnight.

Another day of unsettled weather is expected with the start of the
week. High pressure with a light and variable wind flow across the
region. A low pressure system along a stalled frontal boundary is
expected to move in the Northern Gulf of Mexico. Meanwhile across
South Florida abundant moisture remains with PWATs around 1.9-2
inches. Sea breezes will develop in the afternoon with this being
the main forcing mechanism to initiate convection, Additional
convection will develop along sea breeze and outflow boundary
interactions. Main impacts will continue to be the same across South
Florida with frequent lightning, gusty winds, heavy rainfall and
small hail possible.

Afternoon temperatures will continue to be above normal in the lower
to mid 90s across the area. Heat indices will continue to soar into
the triple digits up to 106.

.Long Term...

Monday Night through Tuesday...

Broad mid/upper troughing will prevail across the southeast States,
with zonally elongated ridging extending from the western Atlantic
through the Bahamas and southeast Gulf of Mexico. A surface front
attendant to the upper wave will remain draped across the coastal
Gulf Coast states, with surface cyclogenesis potentially occurring
somewhere along the frontal zone well to our north. Our location
along the western periphery of the upper ridge will maintain weak
southwesterly flow aloft with light south/southeasterly flow through
the lower troposphere. The reservoir of relatively deep moisture
remains in place, with model forecast precipitable water values
remaining at or above 2 inches through the period. While the mid
levels shouldn't be particularly cool given the ridging in place,
low-level diabatic heating and the aforementioned moisture should
result in plentiful thermodynamic instability and convective
initiation along the inland advancing sea breeze boundaries. Given
the rather light flow pattern thunderstorm development may spread
back towards coastal areas later in the afternoon along colliding
outflow boundaries. It appears that thunderstorm coverage may be a
bit more widespread on Tuesday given slightly deeper moisture and
less influence from the low level ridge. That said afternoon PoPs of
40-50 percent are still anticipated for inland areas each afternoon.
A few stronger storms are possible, and a localized/urban flooding
risk may develop given slow storm motions. Very little change in
temperatures is expected during this period with above average
readings expected. Highs away from the coasts will be well into
the 90s, with lows in the 70s inland and lower 80s along the
coasts. Maximum heat indices of 100 to 108 degrees are likely, so
caution should be exercised by those working outdoors.

Wednesday through Sunday...

The upper trough will gradually lift from the Southeast CONUS into
the mid Atlantic States as ridging at the surface and aloft briefly
expands across the southern Gulf of Mexico and northwest Caribbean
Sea. A low pressure system, potentially with subtropical
characteristics, should be in the vicinity of the coastal Carolinas
early in the period, before pulling away to the north by late week.
However, residual troughing may extend southwest of this feature for
a time. Given deep moisture, light tropospheric flow, and the usual
sea breeze circulation patterns daily shower/thunderstorm
development is anticipated. However, there is some murkiness with
convective trends and coverage by late week depending upon the
evolution of the large scale pattern. It's possible that a more
widespread heavy rain/localized flooding risk could develop during
this time. Keep up with forecast changes. Otherwise the warm pattern
looks to continue with above average temperatures expected.

&&

.Marine...

Generally benign boating conditions continue through the
forecast period for all South Florida coastal waters. Only exception
will be with any thunderstorm that may form, which will bring brief
localized periods of rough seas and gusty winds.

&&

.Aviation (18z TAFs)...

Light winds this morning with some lingering smoke/haze from
fireworks last night trapped in the inversion layer causing some
limited vis. Light winds will continue until both seabreezes
begin to pick up around 16Z. VCTS for all terminals this
afternoon. Sub-VFR conditions for cigs/vis with showers and
storms that move over the terminals, with best chances after 18Z
for east coast. Light winds once again overnight tonight.

&&

.Preliminary Point Temps/PoPs...
West Palm Beach  77  92  78  92 /  60  60  20  50
Fort Lauderdale  80  91  80  91 /  40  40  30  50
Miami            80  93  80  92 /  30  50  20  50
Naples           77  92  78  94 /  20  50  10  40

&&

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

This Afternoon...Cohen
Tonight through Monday and Aviation/Marine...Kelly
Monday Night through Sunday...SPM

Hazardous Weather Outlook for South Florida
National Weather Service Miami FL
326 PM EDT Sun Jul 5 2020

AMZ610-630-650-651-670-671-FLZ063-066>075-168-172>174-GMZ656-657-676-
060730-
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-
326 PM EDT Sun Jul 5 2020

...Strong to Severe Thunderstorms Possible This Afternoon...
...Heat Index Values around 105 This Afternoon...

This hazardous weather outlook is for South Florida.

.DAY ONE...THIS AFTERNOON AND TONIGHT

Thunderstorms: Scattered thunderstorms will affect mainly eastern interior
and east coast metro areas this afternoon and early evening. The
main threats are lightning, gusty winds, small hail, and locally
heavy rainfall.

Waterspouts: Waterspouts are possible this morning with showers in
the Gulf and Atlantic waters. This afternoon showers and
thunderstorms that move over Lake Okeechobee or offshore the Atlantic
waters will be capable of producing waterspouts.

Wind: Thunderstorm wind gusts of 50 mph or greater are possible with
the stronger storms this afternoon and evening.

Hail: Strongest storms will be capable of producing small hail this
afternoon and evening.

Heavy Rainfall: Heavy rainfall is possible in the strongest
thunderstorm activity. Some localized flooding, especially in urban
and poor drainage areas will be possible.

Temperatures: Heat index values around 105 this afternoon over
portions of South Florida.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

Scattered thunderstorms are forecast to affect portions of South
Florida each and every afternoon and evening through the period.
Strong wind gusts, frequent lightning, hail, and torrential rainfall
could accompany this activity. Best chances remain over interior and
east coast areas.

.SPOTTER INFORMATION STATEMENT...

Widespread spotter activation is not anticipated, however individual
spotters are encouraged to report high wind, hail and flooding to
the National Weather Service forecast office in Miami.

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

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