039
FXUS62 KMFL 191355
AFDMFL

Area Forecast Discussion
National Weather Service Miami FL
955 AM EDT Sun May 19 2024

...New UPDATE...

.UPDATE...
Issued at 935 AM EDT Sun May 19 2024

We continue to monitor evolving conditions across South Florida this
morning ahead of a potentially active and stormy afternoon. Data
from the 12z sounding and ACARS flights depict an atmosphere
already primed for convective activity and potentially severe
impacts across the immediate East Coast and Lake Okeechobee
regions.

With MUCAPE > 5000 J/kg, 700-500mb lapse rates above 6
C/km, EBWD > 40 kts, DCAPE > 1000 J/kg and PWATs of 1.65 inches,
damaging wind gusts and severe hail (up to the size of a quarter)
could accompany some of the stronger thunderstorms that could
develop after noontime today. At this time, the limiting factor
for hail development are the mid level temperatures which remain
above -10C. However, temperatures will continue to drop and lapse
rates will steepen as a pronounced shortwave will approach the
region later today, thus enhancing the risk for hail across the
area. A limited risk of tornadoes will also exist with the
activity expected this afternoon, but chances will be limited to
areas where low-level shear exceeds threshold values, namely along
the immediate East Coast sea breeze boundaries.

Models have begun to converge on timing for convective
initiation sometime around/after 2PM, with activity persisting
through sunset. This could allow temperatures to continue to warm
up across the CWA, reaching the mid 90s by early afternoon. Heat
indices are already climbing this morning, and peak apparent
temperatures of 106-110 degrees look probable for at least Miami-
Dade and Broward counties for this afternoon. Given that cloud
cover and rain chances will increase by early afternoon over
northern portions of the area, suspect that these areas should
largely remain below advisory criteria. Nevertheless, would not
be surprised to see localized readings near advisory levels in
portions of Collier and PB counties particularly if
convection/cloud cover is slower to move in than currently
forecast.

&&

.SHORT TERM...
(Today through Monday)
Issued at 225 AM EDT Sun May 19 2024

The mid-lvl ridge which has been positioned over SFL the last couple days
will be displaced southeast of the area today as a pronounced shortwave
trough shifts southeastward toward the area (along with some
lower-amplitude convectively-enhanced perturbations). At the surface,
low pressure will develop off the FL/GA coast with a warm but relatively
weak southwesterly flow prevailing over SFL, which should help pin the
east coast sea breeze near the immediate coast (and perhaps not even
progressing inland at all). The encroaching shortwave will result in
both cooling mid-lvl temperatures and also increasing mid-lvl W-SWrly
flow, which will support an increasingly favorable convective parameter
space over portions of SFL this afternoon. Surface temperatures should
once again increase well into the 90s which along with seasonably cool
500mb temps (-9/-10C) will result in steep lapse rates through the lower
troposphere with SBCAPE values in excess of 3000-3500 J/kg along with
DCAPE > 1200 J/kg progged. As mid-lvl flow increases, 0-6km bulk shear
will likely increase to over 40 kts over northern portions of the area
this afternoon which would favor organized multi-cell clusters with
isolated supercells possible, particularly along any east coast sea
breeze where shear will locally be enhanced.

The main questions regarding convective evolution and the overall severe
threat will be the presence of increasing synoptic cloud cover ahead of
the approaching wave along with the potential evolution/inland progression
of the east coast sea breeze. Even with those question marks, given the
aforementioned environment, there exists a (greater than climo) risk of
large hail, damaging winds, and potentially even an isolated tornado
(mostly dependent upon the sea breeze) with afternoon thunderstorms. The
best chances of severe storms look to be over Palm Beach and Broward
counties where the most favorable intersection between the increasing
forcing, the sea breeze progression, and diurnal timing appears to exist.
This coincides with the latest day 1 outlook from SPC which places a
slight risk over northern portions of the east coast, largely driven by
the wind and hail risk.

The other concern of the day will be excessive heat as the hot air mass
remains in place. It won`t quite be as oppressive as yesterday (which
basically featured record high heat indices for May) but peak apparent
temperatures of 106-110 degrees look probable for at least Miami-Dade
and Broward counties, so another heat advisory has been issued for
those locations. Given that cloud cover and rain chances will increase
by early afternoon over northern portions of the area, suspect that these
areas should largely remain below advisory criteria. That being said,
would not be surprised to see localized readings near advisory levels in
portions of Collier and PB counties particularly if convection/cloud cover is
slower to move in than currently forecast.

The weak low will remain over the Atlantic on Monday and a weak frontal
boundary will shift southward towards the area. This, along with the once
again pinned east coast sea breeze will support scattered to numerous
showers and thunderstorms once again, although reduced instability and
gradually decreasing large-scale ascent (as the trough shifts east)
should support a lower risk of severe storms than Sunday. Although
temperatures and heat indices will remain above normal, they should be a
few degrees lower than Sunday so heat headlines are not expected.

&&

.LONG TERM...
(Monday night through Saturday)
Issued at 225 AM EDT Sun May 19 2024

The weak cold front should finally make it through the area on Tuesday
although a trailing shortwave will likely support at least scattered
showers and storms particularly over southern portions of the area closer
to the boundary. Mid-lvl ridging should then build into the area for the
mid-late week period, with generally light easterly surface flow
prevailing as weak high pressure builds into the Atlantic. Drier air and
the presence of the ridge will keep PoPs lower than the early week period
(largely in the isolated-scattered category), with the synoptic easterly
flow favoring the highest PoPs over the Interior and SW Florida. The
easterly flow will result in cooler (but still above average) high
temperatures over SEFL (mostly upper 80s) while low to mid 90s can be
expected over SWFL and the Interior.

&&

.AVIATION...
(12Z TAFS)
Issued at 721 AM EDT Sun May 19 2024

Sub-VFR conditions could be possible for all terminals this
afternoon as convection overspreads the region, with SHRA/TSRA
likely after 15Z. Short-fuse TEMPOs will likely be needed through
the afternoon especially for East Coast sites. Winds will remain
light and variable this morning, becoming SW at 8-10 kts near
noon-time. There is some uncertainty regarding the inland
intrusion of the Atlantic sea breeze; at this time, erred on the
side of caution with SSE winds at all East Coast sites except KOPF
and KTMB after 18Z. Conditions should improve overnight.

&&

.MARINE...
Issued at 225 AM EDT Sun May 19 2024

Mainly benign marine conditions are expected over the period with light to
moderate southwesterly to westerly flow expected today which will generally
shift to the northwest on Monday as a cold front approaches. Scattered to
Numerous showers and thunderstorms can be expected today, with locally
enhanced winds and seas possible in storms particularly over the Atlantic
waters.

&&

.PRELIMINARY POINT TEMPS/POPS...
Miami            93  78  91  75 /  60  30  70  50
West Kendall     95  75  93  72 /  50  30  60  40
Opa-Locka        94  77  92  75 /  60  30  70  50
Homestead        94  76  92  74 /  40  40  60  50
Fort Lauderdale  91  77  90  75 /  70  40  70  50
N Ft Lauderdale  92  76  90  75 /  70  40  70  50
Pembroke Pines   95  77  93  75 /  70  30  70  50
West Palm Beach  92  74  90  72 /  70  40  60  50
Boca Raton       93  75  91  74 /  70  40  70  50
Naples           91  76  89  74 /  40  40  40  30

&&

.MFL WATCHES/WARNINGS/ADVISORIES...
FL...Heat Advisory until 6 PM EDT this evening for FLZ071>074-172>174.

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

$$

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