709
FXUS62 KJAX 241100
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
700 AM EDT Tue Sep 24 2024

...New AVIATION...

.NEAR TERM...

Clear skies and near calm winds early this morning will see the
potential for some fog to development along inland locations
during the predawn hours. Any fog that does develop should begin
to clear a hour or so after sunrise. Otherwise, another day of
mostly dry conditions as the ridge of high pressure from the past
few days begins to shift off towards the western Atlantic as the
day progresses. Daytime Highs expected in the low 90s along inland
locations with coastal locations in the upper 80s as onshore
winds will keep temperatures a bit cooler. Overnight into
Wednesday, temperature lows will primarily be in the low 70s with
coastal locations a bit warmer in the mid 70s.

~~ MESSAGE OF THE DAY ~~

With another day of quiet weather, review plans and ensure
necessary supplies are assembled in the event of tropical storm or
hurricane impacts later on this week. Please pay close attention
to the forecast information locally as well as from the National
Hurricane Center to stay abreast of the latest forecast
information.

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

&&

.SHORT TERM...(Wednesday through Friday)...

A tropical system (currently Potential Tropical Cyclone Nine, but
forecast to become Hurricane Helene) will begin to accelerate
north- northeastward in the eastern Gulf of Mexico through
Wednesday and is forecast to rapidly intensify into a Major
Hurricane prior to landfall somewhere along the eastern Panhandle
and Big Bend region of Florida Thursday. This will be a broad
system and impacts will extend well away from the cyclone`s center
with impacts beginning locally across Northeast Florida as early
as late Wednesday night and linger through early Friday.

Ahead of the main window of impacts, coastal conditions will
become breezy through Wednesday as gradients begin to tighten
between PTC-9 and a surface high situated to the north. There may
be some convergent bands of showers amid the southeasterly flow
ahead of the actual rainbands spiraling from the accelerating
tropical system. Increasing chances are expected early Thursday as
rain bands begin to push northward across the area.

If timing hold, which is not a certainty given the speed the
system is predicted to gain, the early hours Thursday may be a
period of concern regarding isolated tornadoes. Additional
concerns will be the potential for tropical storm force winds,
flooding rainfall, and at least moderate tidal flooding Thursday
and into Friday.

Despite the relatively fast movement of system, a footprint of 3
to 6 inches of rainfall along the I-75 corridor in NE FL, Suwannee
Valley and interior counties of SE GA is predicted. Undoubtedly,
there will be locally if not scattered areas where amounts are
higher. Given the moderate confidence in excessive rainfall,
elected to hoist a Flash Flood Watch for those aforementioned
areas (this may be expanded eastward with any shifts in the track
to the east).

By Thursday night and through Friday the tropical cyclone will be
pulled to the north and begin to phase with the baroclinic,
stacked low centered to the northwest. The so-called "tail" may
linger across NE FL Friday continuing chances for showers which
may train the area through the afternoon. Power outages and lack
of adequate cooling on Friday may lead to heat impacts as
temperatures rise into the upper 80s and low 90s and heat index
pushing into the lower 100s.

&&

.LONG TERM...(Friday night through next Tuesday)...

What`s left of Potential Tropical Cyclone Nine (PTC-9; likely to
become Tropical Storm Helene) will pull away to the north as it
phases with the near stationary low pressure system along the mid
Mississippi River valley. As it does so, a trailing front will
push south of the area briefly before lifting back to the north
and stalling across northeast Florida through at least early next
week. Southwesterly flow between the broad cutoff upper low to the
northeast and upper ridge east of the Bahamas will steer
shortwave impulses along the aforementioned stationary boundary,
triggering waves of showers and scattered thunderstorms each day.
Though there isn`t a significant amount of cumulative rain
forecast (1-3") with those passing impulses, there may be flood
concerns given the heavy dose of rainfall expected with PTC9 on
Thursday, creating more sensitive conditions this weekend and
early next week. Temperatures will trend down initially and are
expected to hover in the 80s for high temperatures due to
prevailing cloudiness and waves of rainfall.

&&

.AVIATION...
(12Z TAFS)
Issued at 0700 AM EDT Tue Sep 24 2024

VFR conditions through the TAF period. Wind will begin to
redevelop by 15Z-17Z with speeds from 5-10 kts. Winds will again
begin to wane by 00Z on Wednesday night.

&&

.MARINE...

The lingering high pressure will shift off towards the east
through today. Southeasterly winds will begin to increase through
the day getting into the 10-15 kt range by this evening. Come
Wednesday, Small Craft Advisory conditions is expected to develop
during the evening hours. As Potential Tropical Cyclone 9 heads
into the gulf on Wed morning, winds will continue to strengthen
with tropical storm conditions possible by early Thursday and
continue into Thursday night. There is still uncertainty in the
scale, intensity, and track of the tropical system as it develops.
All of those factors will influence the local coastal water
conditions. Some gradual improvement on Friday as the system pulls
away to the north. A trough may linger over the region Friday
night into the weekend with winds and seas below small craft
advisory levels.

Rip Currents: Moderate risk of rip currents this afternoon for
area beaches. High risk of rip currents on for all area beaches by
Wednesday as southeast flow increases as the approach of the
tropical system from the Gulf brings impacts to the local area
waters.

&&

.HYDROLOGY...

Action to minor tidal flooding continues within the St Johns
River basin through mid week before influences from potential
tropical cyclone 9 tracking northward across the eastern Gulf of
Mexico begin. Strong southeasterly flow in response to the
tropical system may bring tidal levels back into Minor or low-end
Moderate flood at times of high tide along the Atlantic coast by
Thursday evening. Given the current elevated tides already ongoing
in the St Johns River, the potential for Moderate Flooding and
impacts are possible during at least Thursday and Friday high
tides. With the potential for increase rainfall from the potential
tropical cyclone, A Flash Flood Watch from Wednesday evening
through Friday morning for locations to the western counties of
the CWA.

Preparations should be considered for low-lying areas along the
St Johns River, especially in the Downtown Jacksonville, San
Marco, & Riverside areas along with other flood prone locations in
the upper St Johns in Clay, St Johns, and Putnam counties.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  91  69  88  72 /   0   0  20  50
SSI  86  76  85  76 /   0   0  10  50
JAX  90  74  88  76 /   0   0  30  60
SGJ  88  76  88  76 /   0   0  30  70
GNV  91  71  89  74 /   0   0  40  70
OCF  93  73  90  76 /   0   0  50  70

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...Flood Watch from Wednesday evening through Friday morning for
     FLZ021-035-120-136-220-236-240-322-340-422-522.

     Coastal Flood Advisory until 5 PM EDT Wednesday for FLZ033-038-
     125-132-137-225-325.

GA...Flood Watch from Wednesday evening through Friday morning for
     GAZ132-133-149-162-163.

AM...None.
&&

$$