740
FXUS62 KJAX 251149
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
749 AM EDT Wed Sep 25 2024

...New AVIATION...

.NEAR TERM...
Issued at 432 AM EDT Wed Sep 25 2024

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

Calm and clear skies will continue through the overnight hours.
By the morning hours, southeast winds will begin to see an uptick
as the pressure gradient over the area begins to tighten as high
pressure settles over the western Atlantic and Helene begins to
move into the Gulf of Mexico. Winds for inland location will range
from 10 to 15 mph with gusts up to 25 mph possible, while coastal
locations will have winds from 15 to 25 mph and gusts up to 30
mph. Showers and thunderstorms during the afternoon to evening
hours as outer rain bands of Helene begin to filter into the area.
The highest rainfall amounts will be found over NE FL as some
locations can get near 1" during the afternoon, with overnight
amounts nearing the 1"-2" range. With the outer bands rotating
into the area, there will be some potential for tornados,
particularly along the coast, but instability will remain on the
weaker side. During the overnight hours, precipitation chances
will increase further as more rain bands continue to arrive to the
area. Some rotation again will be possible within showers and
storms, again coastal locations will be the spot to keep an eye on
for any tornados that develop, but the overall instability will
still be rather on the weak side.

&&

.SHORT TERM...
(Thursday through Friday night)
Issued at 432 AM EDT Wed Sep 25 2024

This will be the most impactful period of weather as Tropical Storm
Helene makes landfall along the Florida Panhandle or Big Bend region
of northeast as possibly a Major Hurricane around sunset Thursday.

Bands spiraling from the broad (soon to be) Hurricane will continue
to push in from south to north across the area bring period of heavy
rain and possibly scattered thunderstorms. Significant rainfall
may lead to periods of flooding, some of which could become
considerable along the Suwannee Valley region in particular
through Thursday night. In addition to tropical storm conditions
and potential hurricane conditions along the I-75 corridor and
into Suwannee Valley, there will also be an Enhanced Convective
risk through Thursday, mainly north of I-10, where scattered
tornadoes may occur within the outer bands (squalls). More
isolated tornado occurrences are possible elsewhere; the tornado
threat will carry through all of Thursday into the nighttime hours
as well.

Helene will race northward after making landfall where it will be
consumed by the large cutoff low to the northwest. Conditions will
quickly improve Friday as the system pulls farther away. There is
uncertainty in where the trailing frontal zone will stall out. Right
now it appears that trailing boundary will stall to the south, which
will usher in a dry slot across the region Friday. Jumping to the
post-event (recovery) period, temperatures will be fairly warm in
the upper 80s to around 90.

&&

.LONG TERM...
(Saturday through Tuesday)
Issued at 432 AM EDT Wed Sep 25 2024

Helene will fully merge with the aforementioned upper low over
the Mississippi River Valley area Friday Night, with a dry slot
across most of the area and a lingering frontal boundary just to
our south. The upper low moves very little through the weekend
while becoming more broad and elongated. Meanwhile, surface high
pressure sits near or just northeast of the northern Bahamas. This
setup will allow a mostly southwesterly flow across the area.
After a pretty short wrap around dry slot southwest of departing
Helene on Friday and Friday Night, layer moisture looks to start
to increase with the southwest flow along the nearly stationary
boundary for the weekend. Guidance currently varies regarding the
position of the boundary and therefore how much drier air remains
entrained over the area aloft for the weekend. Regardless, looks
as though highest rain chances will be over southern areas. Given
the recent wet pattern and Helene passage, leaning towards a
wetter solution for now and therefore included chances for most of
the CWA.

The elongated trough at mid levels looks to make some progress
southeastward into the beginning of next week, which could
continue a push of drier air aloft into the region, as well as
southerly push of the aforementioned boundary to the south of the
area with the development of a more west to northwest flow. The
ECMWF suggests a wetter solution compared to the GFS similar to
the weekend with a more limited southward push of the mid level
trough and surface boundary, though both suggest generally lower
POPs to start next week as compared to the weekend.

Primarily southwest flow for the weekend should keep the area near
to above average temperature wise, followed by closer to normal
for Monday and Tuesday.

&&

.AVIATION...
(12Z TAFS)
Issued at 735 AM EDT Wed Sep 25 2024

Winds will begin to build from out of the southeast by around
14-15z with sustained winds rising to be about 10-15 knots and
gusts reaching upwards of 20-25 knots by around 18-19z. Increased
chances for rainfall and possible thunderstorms this afternoon
with more numerous developments forming ahead of the outer bands
of Helene moving northward from out of the gulf overnight and into
Thursday morning.

&&

.MARINE...
Issued at 432 AM EDT Wed Sep 25 2024

Tropical Storm Helene heads into the gulf this morning.
Southeasterly winds will gradually strengthen through the day
reaching tropical storm strength by Thursday morning, lingering at
these levels into Friday. The tropical system will begin to move
away from the area sometime on Friday. With a trough lingering
over the area into the weekend, conditions are not expected to be
at small craft advisory levels.

Rip Currents: High risk of rip currents on for all area beaches
through Friday as southeasterly flow increases ahead Tropical
Storm Helene over the Gulf of Mexico.

&&

.HYDROLOGY...
Issued at 432 AM EDT Wed Sep 25 2024

A Flood Watch for all of southeast Georgia and northeast Florida
is in effect. Excessive rainfall due to Tropical Storm Helene
will likely result in scattered areas of flash flooding and
isolated episodes of considerable flash flooding, particularly in
urban flood prone locations and areas that received a lot of
rainfall this month. Widespread 3-6" of rain is forecast, with
locally higher amounts. 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.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  88  72  81  72 /  30  80 100  80
SSI  86  75  84  77 /  10  80  90  80
JAX  88  75  86  76 /  30  80  90  80
SGJ  88  76  87  77 /  40  80  90  80
GNV  89  74  84  75 /  60  80 100  70
OCF  91  75  86  77 /  60  80  90  70

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...Tropical Storm Warning for FLZ023-024-030-031-033-038-124-125-
     132-133-136>138-140-225-232-237-240-325-425.

     Hurricane Warning for FLZ021-035-120-220-236-322-340-422-522.

     Flood Watch from this evening through Friday morning for FLZ021-
     023-024-030-031-033-035-038-120-124-125-132-133-136>138-140-
     220-225-232-236-237-240-322-325-340-422-425-522.

     Coastal Flood Advisory until 8 AM EDT Friday for FLZ033-038-125-
     132-137-225-325.

     High Rip Current Risk through Friday evening for FLZ124-125-133-
     138.

GA...Hurricane Warning for GAZ162-163.

     Flood Watch from this evening through Friday morning for
     GAZ132>136-149-151>154-162-163-165-166-250-264-350-364.

     High Rip Current Risk through Friday evening for GAZ154-166.

     Tropical Storm Watch for GAZ132>136-149-151>154-165-166-250-264-
     350-364.

AM...Tropical Storm Warning for AMZ450-452-454-470-472-474.

&&

$$