739
FXUS62 KJAX 151616
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
1216 PM EDT Mon Jul 15 2024

...HEAT ADVISORY TODAY FOR THE COASTAL COUNTIES...
...AFTERNOON AND EVENING STORMS FOCUS ALONG THE I-95 CORRIDOR...

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 1215 PM EDT Mon Jul 15 2024

Early afternoon surface analysis depicts the axis of Atlantic high
pressure (1024 millibars) extending its axis across the FL
peninsula and into the southeastern Gulf of Mexico.
Aloft...ridging was centered off FL`s Atlantic coast, or just
north of the northwestern Bahamas, while troughing was progressing
eastward across the eastern Great Lakes, Ohio and Tennessee
Valleys. Meanwhile, a leftover Mesoscale Convective Vortex (MCV)
from widespread thunderstorm activity that occurred last evening
along the Interstate 4 corridor in central FL was spinning over
the Nature Coast, and this feature was activating isolated
convection along the Gulf coast sea breeze along the FL Big Bend
and Nature Coasts, with a few showers otherwise developing in the
hot and humid air mass along the I-75 corridor in the Suwannee
Valley as well as the U.S. Highway 84 corridor across inland
southeast GA. Latest GOES-East derived Total Precipitable Water
imagery indicates that deep moisture remains in place throughout
our region, with PWATS in the 1.9 - 2.2 inch range. Multi-
layered cloudiness was prevalent closer to the MCV feature across
north central FL, with a healthy cumulus field otherwise
developing across our area. Temperatures at the noon hour were
skyrocketing to the upper 80s and lower 90s, with dewpoints in the
mid to upper 70s creating heat index values that generally ranged
from the upper 90s to around Heat Advisory criteria (108 degrees).

The presence of deep tropical moisture and the aforementioned MCV
feature will trigger scattered to numerous thunderstorms this
afternoon, with activity initially focused along the inland moving
Gulf Coast sea breeze along the I-75 corridor in the Suwannee
Valley and north central FL, with isolated activity developing
elsewhere along differential heating boundaries as well as the
Atlantic sea breeze boundary. Southwesterly low level flow will
tend to slow the inland progress of the Atlantic sea breeze this
afternoon, setting up a collision of outflow boundaries and
eventually the Atlantic and Gulf coast sea breezes for locations
between U.S. Highway 301 and Interstate 95 during the late
afternoon and early evening hours. Storms may pulse as mesoscale
boundaries collide, with stronger activity being capable of
producing downburst winds of 40-50 mph, frequent lightning
strikes, and locally heavy downpours. Steering flow will remain
light, resulting in slow moving storms that could result in
localized flooding, especially if activity moves slowly or
back-builds over urban or normally flood prone locations. Outflow
boundaries will also migrate northward across inland southeast GA
this afternoon, where convection may linger past sunset tonight.

High temperatures this afternoon will soar to the mid and upper
90s, except for north central FL, where thicker multi-layered
cloudiness should keep highs in the lower 90s. Peak Heat Index
values should reach Heat Advisory criteria of 108-112 degrees
behind the inland moving Atlantic sea breeze this afternoon for
the coastal zones in both northeast FL and southeast GA, while
peak values elsewhere mostly reach the 103-107 degree range.
Debris cloudiness from this afternoon and evening`s convection
will gradually thin out overnight, with lows mostly falling to the
mid 70s inland, ranging to around 80 at coastal locations.

&&

.SHORT TERM...(Tuesday through Wednesday Night)

Not much change in the pattern is expected for most of this
period, as a modest south to southwest flow continues to prevail.
The flow is expected to remain just strong enough for the sea
breeze to be mainly pinned near I-95 during peak heating, with the
Gulf sea breeze and other boundary collisions helping to fuel
numerous convection area wide. Temps will also remain generally a
bit above average as well, generally in the mid 90s except near
the immediate coast. Dew points in the mid to upper 70s keep some
areas close to heat advisory levels as well.

&&

.LONG TERM...(Thursday Through Sunday)

Numerous to even widespread convection looks to continue into
most of the long term as a frontal boundary starts to slowly sag
southward and stall just north of the area. An upper trough starts
to dig southward into the southern Plains by the end of the week,
but slows any progress further southeastward as stacked high
pressure ridging remains in place across the FL peninsula in a
blocking-like pattern. There is certainly discrepancies amongst
guidance as to how this trough behaves, especially into this
weekend. However, general outlook will be a persistent south to
southeasterly flow with an unsettled pattern for the long term.
Temperatures are expected to trend near to slightly above normal
during this period.

&&

.AVIATION...
(12Z TAFS)
Issued at 754 AM EDT Mon Jul 15 2024

VFR conditions will prevail at the regional terminals through at
least 17Z. Showers and thunderstorms will begin developing along
the inland moving Atlantic and Gulf coast sea breezes during the
early to mid afternoon hours, with a prevailing low level
southwesterly flow expected to focus convection along the
Interstate 95 corridor late this afternoon. Convection along the
Gulf coast sea breeze may move over the GNV terminal an hour or
two earlier than the rest of the terminals, and a few strong
storms will be possible late this afternoon for the Duval County
terminals, SSI, and SGJ, with localized strong downburst winds,
frequent lightning strikes, and slow moving downpours being
possible within stronger convection. TEMPO groups were placed at
each terminal for brief wind gusts up to 30 knots and IFR
visibilities during heavier downpours, generally between 19Z and
00Z. Convection should then move offshore of the Atlantic coast
towards sunset, with periods of MVFR visibilities developing
overnight at VQQ. Southwesterly surface winds sustained at 5-10
knots will shift to southeasterly and will increase to around 10
knots at the SSI and SGJ coastal terminals after 17Z. Surface
winds will then shift to southerly after convection ends around or
shortly after sunset, with surface speeds diminishing to around 5
knots by 06Z at the coastal terminals and less than 5 knots
inland.

&&

.MARINE...
Issued at 1215 PM EDT Mon Jul 15 2024

The axis of Atlantic high pressure will stretch across the Florida
peninsula through midweek, keeping a prevailing southerly wind
flow in place across our local waters. A few strong thunderstorms
will be possible late this afternoon and early this evening,
mainly over the near shore waters, with stronger storms being
capable of producing briefly strong wind gusts, heavy downpours,
and frequent lightning strikes. Outside of thunderstorm activity,
southerly winds will surge this evening before shifting to
southwesterly and weakening after midnight. A similar weather
pattern will prevail on Tuesday, followed by Atlantic high
pressure sinking southward later this week as a frontal boundary
enters the southeastern states. Seas of 3-5 feet will prevail both
near shore and offshore through Tuesday night. Mainly afternoon
and evening thunderstorms will increase in coverage throughout our
local waters later this week as this boundary stalls to the
northwest of our local waters. Seas will diminish to 2-4 feet
throughout our local waters towards midweek.

Rip Currents: A persistent east-southeasterly ocean swell will
combine with breezy onshore winds during the afternoon hours to
create a moderate rip current risk at all area beaches through at
least midweek.

&&

.FIRE WEATHER...
Issued at 1215 PM EDT Mon Jul 15 2024

Southwesterly transport winds this morning will tend to shift to a
more southerly direction by late afternoon, outside of developing
thunderstorm activity. Stronger thunderstorms will tend to focus
along the Interstate 95 corridor during the late afternoon hours,
with stronger storms later this afternoon being capable of
producing briefly strong wind gusts, frequent lightning strikes,
and slow moving, heavy downpours. Lighter transport winds and
more cloud cover over north central FL will keep daytime
dispersion values generally poor today, with fair to good values
expected elsewhere away from coastal locations. Light
southwesterly transport winds will continue on Tuesday and
Wednesday, with scattered to numerous afternoon and evening
thunderstorms expected across our region.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  96  75  95  75 /  50  30  60  20
SSI  93  78  93  79 /  40  30  60  30
JAX  95  76  96  76 /  70  30  70  30
SGJ  94  77  94  77 /  60  30  70  30
GNV  92  73  93  73 /  80  30  60  20
OCF  93  75  94  75 /  80  40  60  30

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...Heat Advisory until 6 PM EDT this evening for FLZ124-125-133-138.

GA...Heat Advisory until 6 PM EDT this evening for GAZ154-166.

AM...None.
&&

$$