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000
FXUS62 KJAX 280104
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
904 PM EDT Wed Sep 27 2023

...MINOR TO MODERATE TIDAL FLOODING...

....COASTAL SHOWERS FOR NE FL, GUSTY ONSHORE FLOW NORTH OF ST.
AUGUSTINE...

...New UPDATE, HYDROLOGY...

.UPDATE...
Issued at 825 PM EDT Wed Sep 27 2023

A coastal convergent band streaming onshore between St. Augustine
and Palm Coast early this evening extended well offshore to the
NE. Overall rainfall hourly rainfall rates have been < 0.50 inches
with these broken showers and remained low enough to not cause
localized flooding concerns for our coastal communities with the
evening high tide cycle, so cancelled the flood watch early.

Through the night, this convergent band may pivot a bit northward
impacting potentially the Duval county coast with more shower
activity as broad surface low pressure deepens offshore of the
Treasure Coast, but the higher instability and strongest
convergence support coastal shower and possibly isolated t`storms
is expected to focus along the NE FL coast, with convection
generally weakening as it shift farther inland toward the St.
Johns River basin through the night as the 00z JAX RAOB shows a
subsidence inversion near 850 mb (5 kft agl) and backing mid/upper
level flow limiting upper level lift. Mostly cloudy skies will
prevail through the night at the coast, especially for locations
north of St. Augustine where the low level gradient will be
strongest. Winds were still gusting between 25-35 mph from Mayport
to Brunswick this evening. Low temps for coastal areas toward
GNV/OCF will trend above climo in the lower 70s.

Drier, more stable conditions filtered southward across SE GA and
the northern Suwannee River Valley limiting rainfall but
widespread low clouds continue through the night as mild low temps
fall into the mid to upper 60s. Some patchy shallow ground fog is
possible nearing sunrise, but overall mainly expect low stratus.

&&

.NEAR TERM...
Issued at 428 PM EDT Wed Sep 27 2023

An inverted trough is deepening over the coastal waters along the
front that is draped across the area. The pressure gradient
tightens along the GA waters bringing a surge of northeasterly
winds across the waters and along the coast. Showers and storms
will be focused along and south of the boundary mainly across NE
FL. The moist tropical airmass (PWATs 2+ in) will continue the
threat of locally heavy rainfall across coastal NE FL and north-
central FL. A Flood Watch continues for the I-95 corridor as
potentially 1-3 inches could fall on already saturated soils. Weaker
instability and slightly drier air over SE GA has limited
convection today. Moist onshore flow and lift from the front will
continue showers and storms along the frontal boundary as it
shifts southeastward into north central FL. Convection wanes this
evening in the wake of the front. Overnight lows will be in the
mid 60s in inland SE GA to the mid 70s along the NE FL coast.

&&

.SHORT TERM...
(Thursday through Friday night)
Issued at 428 PM EDT Wed Sep 27 2023

Stalled frontal boundary over north-central FL will provide the
primary focus for convection Thursday into Friday. Breezy
northeasterly winds continues as a wedge of surface high pressure
builds down the SE seaboard and an inverted trough over the
coastal waters shifts southward. Moist onshore flow will maintain
the juicy tropical airmass (PWATs ~ 2 in) over NE FL. Meanwhile,
a drier airmass slowly filters in from the north limiting rain
chances to NE FL and coastal SE GA. Convergent bands in the
onshore flow will maintain elevated rain chances along the NE FL
coast into the overnight hours. Temps will be below normal with
highs in the upper 70s to mid 80s and lows in the mid 60s to lows
70s.

&&

.LONG TERM...
(Saturday through next Tuesday)
Issued at 428 PM EDT Wed Sep 27 2023

Surface high pressure remains over the eastern CONUS this weekend
and into early next week. Dry airmass (PWATs ~ 1 in) filtering in
from the north combined with subsidence will lower rain chances
across inland SE GA and Suwannee Valley. Moist northeasterly flow
will continue to bring showers and storms onshore mainly across
the NE FL coast and into north-central FL. Temps will be around
normal with highs in the low to mid 80s and lows in the mid 60s to
low 70s.

&&

.AVIATION...
(00Z TAFS)
Issued at 737 PM EDT Wed Sep 27 2023

Prevailing MVFR ceilings through the forecast period with bases
this evening 1500-2000 ft agl under gusty NE winds 8-10 kts inland
to 13-15 kts with gusts 20-30 kts at the coast. Main focus for
showers will be near SGJ, GNV and CRG over the next few hours,
then just SGJ overnight with < 30% chance near CRG and GNV
through the night.

Increasing confidence of IFR ceilings as winds weaken tonight and
indicated prevailing IFR for JAX, VQQ, CRG and GNV after 07-08z
through 14z Thu when bases will begin to rise back to prevailing
MVFR as gusty NE winds increase once again. Best rain and isolated
TS potential will focus at SGJ through Thu.

&&

.MARINE/COASTAL FLOODING...
Issued at 428 PM EDT Wed Sep 27 2023

A cold front is draped across southeast Georgia waters and will
move southeastward across the northeast Florida waters tonight,
stalling just south of the area on Thursday. A trough of low
pressure is developing along the front towards the coast causing a
surge of northeasterly winds to spread across the coastal waters.
Small craft advisory conditions will prevail through Thursday.
The trough will remain nearly stationary through Friday before
shifting northeast off to sea this weekend. A ridge of high
pressure will then slowly move into area waters Friday and through
the weekend.

The Coastal Flood Watch from Mayport FL northward has been
upgraded to a Coastal Flood Warning due to the both PETSS
and ETSS showing areas along the coast meeting moderate coastal
flooding with this evening`s and tomorrow evening`s high tide
cycles. Coastal Flood Advy was hoisted this morning for the St
Johns river due to the elevated high tides and freshwater inflow
potentially rising to minor flood levels. The coastal flood advy
continues further south along the NE FL coast where areas could
reach minor flood stage.

Rip Currents: Rip current risk is high for area beaches through
Thursday as onshore conditions build. May need to extend this
hazard further out in time due to persistent northeast flow.

&&

.HYDROLOGY...
Issued at 825 PM EDT Wed Sep 27 2023

Update: Evening tides peaked in the Minor to just near Moderate
Flood stage along the coast, with the tide now pushing into the
St. Johns River basin and ICWW where Minor tidal flooding is
expected. The St Simons Island Village Pier peaked near 2.49 ft
MHHW (minor tidal flooding, moderate tidal flooding begins at
2.50 ft MHHW), Fernandina NOS peaked at 2.43 ft MHHW (minor
flooding, moderate begins at 2.50 ft MHHW) and Mayport Bar Pilot`s
station peaked at 1.93 ft MHHW (minor, moderate begins at 2.30 ft
MHHW).

The higher tides are expected through Friday evening for
the coast with the astronomical high tide. For the St. Johns
River basin, the combination of the high astronomical tides and
persistent onshore flow, tidal flooding will likely continue for
an extended duration through at least early next week. Higher
tides for the St. Johns River Basin may begin early next week due
to trapped tides seiche in the river basin.

Previous Discussion: The Coastal Flood Watch from Mayport FL
northward has been upgraded to a Coastal Flood Warning due to the
both PETSS and ETSS showing areas along the coast meeting moderate
coastal flooding with this evening`s and tomorrow evening`s high
tide cycles. Coastal Flood Advy was hoisted this morning for the
St Johns river due to the elevated high tides and freshwater
inflow potentially rising to minor flood levels. The coastal flood
advy continues further south along the NE FL coast where areas
could reach minor flood stage.

Rip Currents: Rip current risk is high for area beaches through
Thursday as onshore conditions build. May need to extend this
hazard further out in time due to persistent northeast flow.



&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  66  78  66  84 /  10  10  10  10
SSI  72  78  72  82 /  30  20  20  20
JAX  71  80  70  82 /  40  30  20  30
SGJ  74  82  72  82 /  60  60  40  50
GNV  71  83  70  83 /  30  30  20  40
OCF  72  84  71  84 /  30  70  20  40

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...Coastal Flood Advisory until 11 PM EDT Friday for FLZ033-038-132-
     133-137-138-225-325.

     Coastal Flood Warning until 11 PM EDT Friday for FLZ124-125.

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

GA...Coastal Flood Warning until 11 PM EDT Friday for GAZ154-166.

     High Rip Current Risk through late Friday night for GAZ154-166.

AM...Small Craft Advisory until 6 PM EDT Thursday for AMZ450-452-470-
     472.

&&

$$