967
FXUS62 KJAX 021637
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
1237 PM EDT Tue Jul 2 2024

...STRONG STORMS AND HEAVY DOWNPOURS LATE THIS AFTERNOON AND
EVENING FOR LOCATIONS ALONG THE INTERSTATE 75 CORRIDOR...
...SCATTERED TO NUMEROUS AFTERNOON AND EVENING STORMS ON WEDNESDAY
AND INDEPENDENCE DAY...
...DANGEROUS HEAT INDEX VALUES FROM FRIDAY THROUGH MONDAY...

For the latest NE FL and SE GA Daily Key Messages please visit:
https://www.weather.gov/media/jax/briefings/nws-jax-briefing.pdf

.UPDATE...
Issued at 1235 PM EDT Tue Jul 2 2024

Early afternoon surface analysis depicts a stalled and weakening
frontal boundary positioned across the Deep South. Meanwhile, high
pressure (1027 millibars) centered over the eastern Great Lakes
extends southward down the spine of the Appalachian mountains.
Aloft..."Heat Wave" ridging continues to build eastward from the
lower Mississippi and Tennessee Valleys towards the southeastern
seaboard as troughing departs the New England and Mid-Atlantic
coasts. Latest GOES-East derived Total Precipitable Water imagery
indicates that deep moisture remains in place throughout our
region, with PWAT values mostly in the 1.9 - 2.1 inch range, while
a much drier air mass exists to the north of the frontal boundary
across the Carolinas and northeastern GA. Scattered and slow
moving convection developed late this morning just south of the
stalled front across inland portions of southeast GA, with widely
scattered showers and thunderstorms also developing along the
Atlantic sea breeze boundary that is positioned along the
northeast FL coast. Thick, multi-layered cloud cover was located
across inland southeast GA for locations north of Waycross, which
was keeping temperatures in the 75-80 degree range, while
temperatures elsewhere outside of ongoing convection were
generally in the 85-90 degree range as of 16Z.

The presence of the stalled frontal boundary, differential heating
due to cloud cover north of the Okefenokee Swamp, and mesoscale
boundary collisions in a deeply moist air mass should allow for
convective coverage to increase across southeast GA through the
mid to late afternoon hours. Slow movement of convection may
result in localized flooding, especially where heavy downpours
train over urban areas such as Brunswick and Waycross, or over
normally flood prone locations. The Weather Prediction Center has
placed all of southeast GA and most of northeast FL within a
"Marginal" risk of Excessive Rainfall today (Level 1 of 4) for
this isolated flooding probabilities. Further south, plenty of
insolation this morning has destabilized the atmosphere, setting
the stage for scattered to numerous showers and thunderstorms this
afternoon and evening.

High pressure wedging down the southeastern seaboard will
increase low level easterly flow somewhat later this afternoon,
providing an inland push to the Atlantic sea breeze boundary. The
Gulf coast sea breeze will also push inland towards Interstate 75
towards sunset, setting up a collision of these sea breezes that
will result in increasing chances for convection, mainly for
locations west of the I-95 corridor. Storms will pulse in an
environment that features ML CAPE values of 1,500 - 2,500 j/kg for
locations along and south of I-10, with stronger storms this
afternoon and evening being capable of producing downburst winds
of 40-50 mph, frequent lightning strikes, and localized flooding
due to slow movement of thunderstorms. Highs this afternoon will
remain in the mid to upper 80s for locations north of Waycross,
with upper 80s and lower 90s elsewhere, except mid 90s for
portions of north central FL. Peak heat index values should remain
just below Heat Advisory criteria in northeast and north central
FL, with maximums generally in the 103-107 range.

Convection may be slow to wind down for locations west of the U.S.
Highway 301 corridor this evening as mesoscale boundary collisions
continue. Also, light onshore winds could develop isolated
convection at coastal locations during the overnight and predawn
hours on Wednesday. Low stratus ceilings are expected to develop
towards sunrise across inland southeast GA due to the presence of
the weakening frontal boundary. Lows tonight will fall to the low
and mid 70s at inland locations, with coastal lows in the upper
70s to around 80.

&&

.SHORT TERM...
(Wednesday through Thursday night)
Issued at 415 AM EDT Tue Jul 2 2024

Weak, nearly stationary frontal boundary lays generally west to
east across eastern GA on Wednesday and will briefly be stalled.
Sfc high pressure will gradually build north of the boundary by
Thursday helping to push the diffuse boundary southward into
northeast FL. Mid to upper level ridge will be parked over the
southeast states Wednesday through Wednesday night and then
slightly retrograde on Thursday as some mid level troughing drops
in over SC and eastern GA. PWATs are still forecast to remain
elevated at about 2 to 2.3 inches on Wednesday with mean steering
flow from the east but only at 5-10 knots. With sea breezes,
daytime heating, and the weak frontal boundary, numerous showers
and thunderstorms are expected Wed and will fade in coverage Wed
night. Locally heavy rainfall and gusty winds expected with the
stronger storms mainly inland areas, given the push of the
easterly flow moving storms inland.

Thursday, shower and storm coverage remains in the scattered to
numerous range with the frontal boundary shifting southward, and
the axis of higher precip chances drifting southward as well. The
lighter synoptic flow and PWATs of at least 2 inches will support
locally heavy rainfall/localized flooding. Some drier air will
likely be working in from the northeast late Thu into Thur night
as the mid level trough from SC pushes deeper moisture further
southward.

High temps both Wed and Thu expected in the lower 90s most areas
with heat indices topping out around 104-108, so near or just
below heat advy criteria. This will need to be monitored but at
this time not enough area to indicate advisories would be
warranted. Lows generally in the mid 70s given the soupy airmass
and debris clouds from daytime convection.

&&

.LONG TERM...
(Friday through Monday)
Issued at 415 AM EDT Tue Jul 2 2024

Mid to upper layer ridging will prevail over the area Friday through
the weekend, with some drier air continuing to work into the area
from the east and northeast Friday and Saturday. The mid level ridge
will shift southeastward on Monday as mid level troughing drops
into the Great Lakes and most of the MS valley area. Sfc ridge
will be across north central FL area Friday and slowly shift
southward over the weekend and into Monday. Sea breezes and
daytime heating expected to support generally just scattered
showers and storms each day, but drier air Fri and Sat and warm
temps aloft could potential result in just widely scattered
(25-30 percent) coverage. Best coverage of storms looks to be
near and west of Highway 301 over northeast FL Friday through
Sunday. A slight uptick in rain chances for most zones is
indicated for Monday as deep moisture levels rise over the area.
Ridging and drier air will allow high temperatures to quickly rise
into the mid/upper 90s through the weekend. Heat indices will
likely rise into heat advisory criteria by the weekend.

&&

.AVIATION...
(12Z TAFS)
Issued at 829 AM EDT Tue Jul 2 2024

VFR conditions will prevail at the regional terminals through at
least 16Z. Isolated showers may develop near SSI and the Duval
County terminals this morning, with brief periods of MVFR ceilings
possible. Showers and thunderstorms will then develop along the
Interstate 95 corridor along the inland moving Atlantic sea breeze
boundary shortly after noon. PROB30 groups were maintained through
the afternoon hours at SSI and the Duval County terminals, with
lower confidence for impacts at SGJ, where vicinity coverage was
used at the PROB30 group was eliminated. Higher probabilities for
IFR impacts and brief wind gusts around 30 knots are expected
late this afternoon through early this evening at VQQ and GNV,
where the Atlantic and Gulf coast sea breezes will collide towards
sunset tonight along the U.S. Highway 301 corridor. PROB30 groups
were maintained at these two terminals through around 02Z for
now, but will likely be upgraded to TEMPO groups for the 18Z TAF
package. Thunderstorm coverage at the inland terminals should
dissipate before 04Z, with MVFR visibilities likely to develop at
VQQ before 06Z. VFR conditions should otherwise prevail overnight
at the regional terminals. Light and variable winds through around
14Z will shift to southeasterly before noon, with speeds outside
of thunderstorm activity expected to remain in the 5-10 knot range
at the inland terminals, with speeds increasing to around 10 knots
at the SGJ and SSI coastal terminals after 17Z.

&&

.MARINE...
Issued at 1235 PM EDT Tue Jul 2 2024

A frontal boundary will remain stalled over the Georgia waters
through Wednesday. Prevailing winds will shift to easterly this
afternoon as high pressure building over the Mid-Atlantic states
wedges down the southeastern seaboard. Showers and thunderstorms
will increase in coverage across our local waters along and south
of this stalled frontal boundary through Wednesday. The frontal
boundary will gradually dissipate over the Georgia waters by
Thursday, with prevailing onshore winds continuing as high
pressure weakens off the eastern seaboard. Coverage of showers and
thunderstorms are expected to decrease across our local waters
late this week through Saturday, with prevailing winds then
shifting to southwesterly during the weekend ahead of the next
weakening frontal boundary that will be entering the southeastern
states. Seas of 2 to 4 feet will prevail both near shore and
offshore during the next several days.

Rip Currents: Onshore winds will become breezy this afternoon at
area beaches and will combine with a lingering east-southeasterly
ocean swell to create a low-end moderate rip current risk. This
moderate risk is expected to continue at all area beaches through
Independence Day.

&&

.FIRE WEATHER...
Issued at 1235 PM EDT Tue Jul 2 2024

Light and generally easterly transport winds will continue through
Wednesday, with scattered to numerous afternoon and evening
showers and thunderstorms and more extensive cloud cover keeping
daytime dispersion values in the poor to fair range throughout our
region. Mixing heights will begin to rise on Thursday, but
generally light transport wind speeds will keep daytime dispersion
values in the fair range at most locations during the afternoon
hours.

&&

.HYDROLOGY...
Issued at 400 AM EDT Mon Jul 1 2024

High moisture (PWATs ~2.3 inches) over the region will lead to
heavy downpours from convection especially along and ahead of an
approaching frontal boundary/trough from the north. WPC has placed
SE GA and small area of northeast FL in a marginal risk of
excessive rainfall today. Localized areas could see rain amounts
of 3 inches in a short period of time.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  89  74  91  74 /  80  60  70  30
SSI  87  79  89  79 /  50  50  50  30
JAX  92  75  92  75 /  60  30  70  20
SGJ  91  77  91  78 /  50  40  40  20
GNV  93  73  93  75 /  70  50  80  40
OCF  93  74  92  75 /  70  50  70  40

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...None.
AM...None.
&&

$$