Flood and Heavy Rain in Florida, September 14, 2024

Area Forecast Discussion
National Weather Service Jacksonville FL
1228 PM EDT Sat Sep 14 2024

...New AVIATION...

.UPDATE...
Issued at 941 AM EDT Sat Sep 14 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

This afternoon/evening...Wave of energy aloft over the NE Gulf
will track into NE FL with a slow wiggle northward of frontal
boundary into the local area, while at the surface a surge of
breezy Northeast winds flowing southward across SE GA will meet
the old frontal boundary near the FL/GA border and expect numerous
to widespread shower activity to break out, along with a few
embedded storms with locally heavy rainfall continuing as the main
impact, although a few strong storms with some gusty winds to
40-50 mph cannot be ruled out. Main corridor for the heavy
rainfall threat will be from the I-10 corridor of NE FL northward
across SE GA and will keep Flood Watch in place across inland SE
GA for now, although heavy rainfall/localized flooding threat
could occur anywhere these two systems meet. Max temps generally
topping out in the 80s, at slightly below normal levels. Along
with the rainfall impact, Northeast winds will become breezy along
the Atlantic Coastal areas, mainly along the SE GA coastal
counties where NE winds will increase to 15-20G25-30 mph range
through the afternoon/evening hours.

Tonight...After sunset, the energy aloft will shift East of the
region and inland storm activity will fade, but the old frontal
boundary at the surface will be left behind across NE FL with a
continued North to Northeast flow at the surface and expect at
least scattered shower activity to linger across many locations
with best chances along the Atlantic Coast from Brunswick to
Jacksonville where some isolated storms will also be possible and
some heavy downpours will continue to be possible in any coastal
convergent bands that develop through the overnight hours. Further
inland south of the frontal boundary across inland NE FL/I-75
corridor, some patchy fog will be possible, but enough low level
flow should be around to keep it from become dense. Low temps will
generally be in the lower 70s inland and mid/upper 70s along the
Atlantic Coast.

&&

.SYNOPSIS...
Issued at 428 AM EDT Sat Sep 14 2024

Early morning surface analysis depicts a persistent, wavy and
nearly stationary frontal boundary extending across the FL
panhandle, Big Bend, and Nature Coast eastward across the
Interstate 4 corridor. Meanwhile, weak low pressure (1009
millibars) was poised to organize over the Gulf Stream waters off
the Carolina coast. Otherwise, high pressure (1023 millibars)
remains situated along coastal New England, with a stronger high
pressure center (1030 millibars) building southward from Quebec.
Aloft, a "Rex Block" has become established over the eastern half
of the nation, with ridging becoming anchored over the eastern
Great Lakes, trapping Francine's remnant trough to the south over
the Ozarks and the lower Mississippi River Valley. Latest GOES-
East derived Total Precipitable Water imagery indicates that a
slightly drier air mass has temporarily advected into our region
from the west, with PWAT values falling to the 1.7 - 1.9 inch
range for most locations. Isentropic lift associated with
Francine's remnant trough was developing low-topped showers for
locations west of Alma and north of Homerville in interior
southeast GA. Low stratus ceilings have overspread much of
the Suwannee Valley and southeast GA, with patchy fog developing
along and east of U.S. Highway 301 in northeast and north central
FL. Temperatures and dewpoints at 08Z were in the 70s area-wide.

&&

.NEAR TERM...
(Today and Tonight)
Issued at 428 AM EDT Sat Sep 14 2024

Low stratus and patches of locally dense fog are expected to
expand at inland locations through the early morning hours today.
Meanwhile, shower activity over inland southeast GA will persist
this morning for locations from Alma westward across Douglas,
Pearson, and Hazelhurst. Fog and low stratus will erode by the
mid-morning hours.

The remnant trough associated with Francine will meander over the
Deep South this weekend as low pressure gradually organizes over
the Gulf Stream waters off the southeastern seaboard. Our local
pressure gradient will begin to tighten from north to south this
afternoon and tonight as reinforcing, strong high pressure over
eastern Canada and New England wedges down the southeastern
seaboard. The leading edge of this wind surge will likely develop
slow moving downpours and embedded thunderstorms by early
afternoon across southeast GA, with activity then expanding along
the I-95 corridor in northeast FL during the early to mid
afternoon hours before shifting towards I-75 corridor later this
afternoon. Slow moving downpours may result in localized flooding,
with the flood threat being high enough due to saturated soils
from heavy downpours on Friday afternoon and evening to warrant a
Flood Watch for locations from Alma westward this afternoon, where
1-2 inches of rainfall and localized totals of 3-4 inches cannot
be ruled out through early this evening. Rainfall amounts of 0.5 -
1 inch appear likely elsewhere, but locally higher totals may
result in localized flooding, especially at urban and normally
flood prone locations. A few breaks in the multi-layered
cloudiness later this morning and early this afternoon should
boost highs to the mid to upper 80s, with a few locations
approaching 90 in north central FL, where heat indices could reach
100 this afternoon.

Onshore winds will remain breezy tonight at coastal locations as
low pressure continues to organize over the Gulf Stream waters off
the Carolinas. Convergent low level onshore winds may organize a
band of convection towards sunrise along the southeast GA coast,
with evening convection along the I-75 corridor and inland
portions of southeast GA expected to dissipate before midnight.
Low stratus clouds will likely develop at inland locations during
the predawn hours, with patches of locally dense fog possible
along and west of the I-75 corridor in the Suwannee Valley and
north central FL. Lows tonight will only fall to the low and mid
70s inland, while breezy onshore winds keep coastal lows in the
upper 70s.

&&

.SHORT TERM...
(Sunday through Monday)
Issued at 428 AM EDT Sat Sep 14 2024

The local gradient tightens as high pressure wedges down the
eastern seaboard and a low pressure system off the coast of the
Carolinas strengthens and approaches the Carolinas coast.
Meanwhile, the low's associated frontal boundary remains draped
across northern FL. A lingering moist airmass, convergence along
the frontal boundary, and upper energy from the remnants of
Francine will support daily scattered to numerous showers with
embedded thunderstorms. Slight decrease in convective coverage
over NE FL on Sunday due to mid-level dry air being ushered in
around the south side of Francine's remnants. Breezy northeasterly
winds develop with gusts of 20 mph along the coast. Highs will be
in the low 80s in SE GA to around 90 in north-central FL.
Overnight lows will be in the upper 60s and low 70s.

&&

.LONG TERM...
(Tuesday through Friday)
Issued at 428 AM EDT Sat Sep 14 2024

Frontal boundary remains over north FL through Wednesday as its
associated low potentially moves onshore to the Carolinas and
into the Mid-Atlantic region. There is a medium chance that this
low could gradually acquire subtropical or tropical
characteristics and there is still uncertainty with its track and
intensity. The wet pattern continues through mid-week next week
with scattered to numerous showers and storms. Rain chances then
decrease as drier air filters into the region for the end of the
work week as the front sinks southward down the FL peninsula.
Temperatures will be around seasonal with highs in the 80s and
lows in the upper 60s and low 70s.

&&

.AVIATION...
(18Z TAFS)
Issued at 1216 PM EDT Sat Sep 14 2024

Convection breaking out across the TAF site area in NE FL/Coastal
SE GA with numerous to widespread showers expected and TEMPO's
will be needed for all TAF sites in the 19-23Z time frame for
potential TSRA activity, as conds will be mainly MVFR with TEMPO
IFR VSBYS in TSRA activity. Northeast flow will slowly increase at
SSI to 14g21kt this afternoon, with lesser NE winds at NE FL TAF
sites. After sunset time frame (around 00Z) this evening expect
TSRA chances to fade back to lingering showers (VCSH) through the
overnight hours at SSI/JAX/CRG/SGJ, while the inland TAF sites of
VQQ are expected to drop to IFR CIGS after 06Z and LIFR CIGS at
GNV. Shower activity will increase after 15Z on Sunday and will
add PROB30 groups for this potential increase at SSI/JAX/CRG
towards the end of the period.

&&

.MARINE...
Issued at 428 AM EDT Sat Sep 14 2024

High pressure centered off the New England coast will be
reinforced by a stronger high pressure center on Sunday, with this
feature wedging down the southeastern seaboard through early
portions of the upcoming week. Meanwhile, low pressure will
develop over the Gulf Stream waters adjacent to the southeastern
seaboard on Sunday, with this system potentially acquiring
tropical characteristics early in the upcoming week as it moves
northwestward towards the Carolina coast. Otherwise, a stationary
frontal boundary will remain situated just south of our local
waters through midweek, bringing episodes of showers and
thunderstorms.

Strengthening northeasterly winds and building seas will bring
Small Craft Advisory conditions to the offshore Georgia waters
this afternoon, where wind speeds will increase to around 20
knots, with seas building to Caution levels of 4-6 feet this
afternoon and then 5-7 feet tonight. Caution conditions are expected
for the near shore Georgia waters this afternoon, as wind speeds
increase to 15-20 knots and seas build to 3-5 feet this afternoon,
building further to 4-6 feet tonight. Small Craft Advisory
conditions will then overspread the rest of our local waters on
Sunday and Sunday night as northeasterly winds continue to
strengthen and seas build. Seas will peak in the 7-10 foot range
offshore on Monday and Monday night, with 5-7 foot seas near
shore. Winds and seas will then gradually diminish towards
midweek as low pressure pivots northward across the coastal
Carolinas and moves towards the Mid- Atlantic states.

Rip Currents / High Surf: Strengthening onshore winds this
afternoon will combine with a persistent northeasterly ocean
swell to create a high rip current risk at all area beaches. Surf
heights will continue to build on Sunday, and a High Surf Advisory
may be required by Monday at the northeast FL beaches, where
breakers will build to 4-5 feet on Sunday and 6-7 feet on Monday.
A high rip current risk will likely persist through Tuesday at
area beaches.

&&

.HYDROLOGY...
Issued at 428 AM EDT Sat Sep 14 2024

Slow moving downpours and embedded thunderstorms are expected
across portions of inland southeast GA this afternoon. Saturated
ground conditions for locations from Alma westward will exacerbate
the Flood potential, and a Flood Watch has been issued through
early this evening. 1-2 inches of rainfall are expected within the
Flood Watch area today, with localized totals of 3-4 inches
possible. Slow moving downpours and embedded thunderstorms
elsewhere this afternoon and evening may result in localized
flooding, especially at urban and normally flood prone, low-lying
areas. This localized flood potential will likely extend into
early portions of the upcoming week, as waves of downpours
potentially stream onshore from the Atlantic waters due to
strengthening onshore winds.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  82  70  81  68 /  60  40  40  30
SSI  82  74  82  72 /  60  60  60  40
JAX  85  73  83  72 /  80  50  40  40
SGJ  86  74  85  74 /  80  40  40  40
GNV  87  71  87  71 /  60  20  40  20
OCF  89  72  89  72 /  70  20  40  20

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...Coastal Flood Advisory until 5 PM EDT Sunday for FLZ033-038-132-
     137-325.

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

GA...High Rip Current Risk through Monday evening for GAZ154-166.

     Flood Watch until 8 PM EDT this evening for GAZ132>134-149.

AM...Small Craft Advisory until 5 AM EDT Tuesday for AMZ450-470.

&&