Severe Thunderstorm Warning 66, NWS Miami, FL

Area Forecast Discussion
National Weather Service Miami FL
122 PM EDT Sat Jun 17 2023

...New LONG TERM...

.SHORT TERM...
(Rest of today through Sunday)
Issued at 1249 PM EDT Sat Jun 17 2023

Unsettled weather continues today as an upper level trough amplifies
over the southeast US and a mid-level shortwave slides over South
Florida. Scattered to numerous showers and thunderstorms will impact
much of South Florida this afternoon as sea-breeze driven convection
combines with the remnants of an MCS to our north as they advect
into the area. Latest mesoanalysis this morning shows an area of
robust instability (CAPE > 3000 J/kg), strong shear (EBDW ~35-45
kts), moderate lapse rates (6-7 C/km) and enhanced PWATs (up to 2
inches) moving into our area, which will bolster the chance for a
few strong to severe storms. With the environmental conditions as
they area, damaging winds will be the more likely severe impacts
with these storms, although small hail (up to the size of a quarter)
and a few funnel clouds cannot be ruled out, especially along
boundary collisions and the East Coast sea breeze. Flooding will
also be a concern for the East Coast metro areas as multiple rounds
of storms and even some backbuilding could result in continued
rainfall.

With the shortwave advecting eastward away from the region tonight
into Sunday, the best dynamics for strong to severe storms will
depart. However given the continued southwesterly flow of moist and
unstable air across the region, shower and thunderstorm chances will
remain elevated in nature. A few of the CAMs indicate the potential
for nocturnal shower and thunderstorm activity to persist into the
overnight hours into early Sunday, followed by an additional round
of diurnal showers and thunderstorms during the afternoon hours.
Although convection is not anticipated to be as robust as today
given warmer 500mb temperatures and less steep lapse rates, stronger
winds aloft could lead to a few storms become severe in nature, with
damaging winds and an isolated tornado possible.

Temperatures and heat indices will remain exceedingly warm today and
tomorrow. Temperatures this afternoon are expected to reach the low
to mid 90s across the East Coast and lower 90s over the interior and
southwest, while heat indices could approach the 103-105 range along
the East Coast. Increased cloud coverage with storms will bring some
relief to areas impacted, helping keep conditions below record
values.

&&

.LONG TERM...
(Sunday night through next Friday)
Issued at 120 PM EDT Sat Jun 17 2023

An active yet increasingly complex synoptic evolution will continue
into early next week, as mid-level ridging over the western Gulf of
Mexico will gradually give way to a retrograding cut-off low/Rex
Block set-up mid-late week. All the while, low-lvl W-SWrly flow will
continue to supply deep tropical moisture.  As mentioned in previous
long term discussions, the predictability and evolution of each of
these synoptic features and the upstream implications of their
strength and positioning could alter our weather here in South
Florida greatly.

Monday: To start the period we will remain in the mid-lvl NWrly flow
regime as we remain downstream of the south-central US ridge.
Convectively-enhanced disturbances will continue to crest the ridge
and will interact with the climatologically rich moisture (PWATs
generally 75-85th percentile) and a likely pinned sea-breeze
boundary near the east coast. If the disturbance phases well with
peak heating strong-severe storms will be possible, as well as
localized flooding concerns along the immediate east coast due to
the pinned boundary. It will be quite hot prior to convective
initiation, with highs in the low to mid 90s and heat indices
approaching advisory criteria Monday afternoon.

Tuesday/Wednesday: The mid-week period will see the pattern shift as
the cut-off low sets up to our north and meanders over the northern
gulf coast. The focus for precipitation will remain the eastern half
of the area, given the continued SWrly steering flow and convergence
along the nearly-pinned east coast sea breeze. Heavy rainfall and
locally strong storms remain a threat, with some of the convective
potential dependent upon areas of vorticity ejecting around the cut-
offs southern periphery.

Thursday/Friday: The cut-off low may retrograde a bit west late in
the period, although given the low-predictability nature inherent to
these types of patterns this is not high confidence. This will
enable high pressure over the eastern US to build westward,
resulting in some backing of the low-lvl flow more S-SErly. The
enhanced southerly flow between the Atlantic high and the western
low may enable subtropical moisture to funnel the area
Thursday/Friday maintaining the enhanced rain chances (with a
potential continued hydro risk). Temperatures may decrease to near
climo by this period due to increased cloud cover and a somewhat
cooler airmass.

&&

.AVIATION...
(18Z TAFS)
Issued at 1249 PM EDT Sat Jun 17 2023

Periods of sub-VFR conditions will materialize this afternoon as
scattered to numerous showers develop near terminals sites. Have
first round of TEMPOs in place but more amendments could needed
as conditions evolve. Showers could linger overnight, with
additional chances of storms tomorrow. Breezy southwesterly winds
could give way to more southerly flow at East Coast sites this
evening, before returning from the SW tomorrow.

&&

.MARINE...
Issued at 1249 PM EDT Sat Jun 17 2023

A generally moderate to robust south to southwesterly flow in the 10
to 15 kt range is expected to continue across the Atlantic marine
zones, and around 5 to 10 kt over the Gulf waters through the
weekend. Expect seas mainly around 2 feet or less over the Gulf
waters and 3 feet or less over the Atlantic waters. Scattered
showers and thunderstorms will be possible each day, with higher
chances Saturday and Sunday. Any thunderstorms that form could
produce brief periods of rough seas and gusty winds.

&&

.PRELIMINARY POINT TEMPS/POPS...
Miami            77  92  79  93 /  70  70  40  70
West Kendall     76  93  76  94 /  60  60  30  70
Opa-Locka        76  92  78  93 /  60  70  40  70
Homestead        76  91  76  92 /  60  60  30  60
Fort Lauderdale  76  91  77  91 /  60  70  40  70
N Ft Lauderdale  76  92  78  92 /  60  70  40  80
Pembroke Pines   76  92  77  93 /  60  70  40  70
West Palm Beach  75  91  76  93 /  50  80  50  80
Boca Raton       76  93  76  93 /  60  70  50  80
Naples           81  91  81  92 /  60  80  50  60

&&

.MFL WATCHES/WARNINGS/ADVISORIES...
FL...Heat Advisory until 7 PM EDT this evening for FLZ063-066>075-168-
     172>174.

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

SHORT TERM...ATV
LONG TERM....Carr
AVIATION...ATV

Hazardous Weather Outlook
National Weather Service Miami FL
952 AM EDT Sat Jun 17 2023

AMZ610-630-650-651-670-671-FLZ063-066>075-168-172>174-GMZ656-657-676-
181400-
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 County-Metro Palm Beach County-
Coastal Collier County-Inland Collier County-Inland Broward County-
Metro Broward County-Inland Miami-Dade County-
Metropolitan Miami Dade-Mainland Monroe-Coastal Palm Beach County-
Coastal Broward County-Coastal Miami Dade County-Far South Miami-
Dade County-
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-
952 AM EDT Sat Jun 17 2023

This Hazardous Weather Outlook is for Atlantic coastal waters,
southeast Florida, southern Florida, southwest Florida and Gulf of
Mexico.

...A Few Strong To Severe Thunderstorms Possible Today...
...Potential for Localized Flooding for East Coast Metro...
...Heat Indices in the Triple Digits This Afternoon...

.DAY ONE...Today and tonight.

Thunderstorms: Scattered to numerous thunderstorms are possible
today. A few could become strong to severe in nature, with the
potential of damaging wind gusts, small hail (up to the size of a
quarter), and frequent lightning. An isolated funnel cloud cannot be
ruled out as well.

Flooding: With the potential for heavy downpours with storms today
and additional rounds of activity, localized flooding will be
possible especially across the east coast metro areas.

Heat Index: Peak heat indices are expected to reach or exceed 105
degrees this afternoon, with potential for localized values
approaching 108 to 110 degrees. A Heat Advisory is in effect for
most of South Florida this afternoon.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Scattered to numerous thunderstorms will be possible each day
through the middle of the week. The strongest storms could contain
heavy downpours, gusty winds, small hail, funnel clouds and frequent
lightning.

Peak heat indices in the 104-107F range will be possible each day
through Monday.

The risk of rip currents increases for Gulf Coast beaches on Sunday.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report high wind, hail, and
flooding to the National Weather Service forecast office in Miami.

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