545
FXUS62 KJAX 171532
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
1132 AM EDT Sun Aug 17 2025

...HEAVY DOWNPOURS AND LOCALIZED FLOODING POSSIBLE ACROSS
NORTHEAST AND NORTH CENTRAL FL THIS AFTERNOON AND EVENING...
...POWERFUL OCEAN SWELLS FROM DISTANT MAJOR HURRICANE ERIN ARRIVE
AT AREA BEACHES ON MONDAY AFTERNOON...
...MINOR COASTAL FLOODING AND MODERATE BEACH EROSION POSSIBLE ON
WEDNESDAY AFTERNOON AND EVENING...

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 1133 AM EDT Sun Aug 17 2025

Late morning surface analysis depicts a weak frontal boundary /
surface trough situated along the Interstate 10 corridor.
Meanwhile, weakening high pressure (1018 millibars) stretches
from coastal New England southwestward through the Tennessee and
lower Mississippi River Valleys. Otherwise, strong high pressure
(1028 millibars) was building southeastward across the Great Lakes
region. Aloft..."Heat Wave" ridging stretches from the Mid-
Mississippi Valley southward through the Ozarks to Texas, while
troughing over the southeastern states was poised to cutoff from
the main flow pattern over our region as another potent shortwave
trough traverses eastern portions of the Great Lakes. Latest
GOES-East derived Total Precipitable Water imagery indicates that
deep tropical moisture remains in place across our area, with
PWATs generally ranging from 2 - 2.25 inches. Substantially drier
air was located just north of the Altamaha River basin in GA as
well as south of the Interstate 4 corridor in the FL peninsula.
Convection has been firing along the aforementioned weak
stationary boundary /surface trough over the Atlantic waters
adjacent to northeast FL, with this activity recently moving
onshore along portions of the Duval and northern St. Johns County
coastlines. Low stratus ceilings have been surprisingly stubborn
to lift across a good portion of northeast and north central FL
this morning, with temperatures beneath this thick cloud cover
remaining in the upper 70s to around 80 late this morning in the
Suwannee Valley. Multi-layered cloudiness prevails elsewhere, with
temperatures slowly climbing through the low and middle 80s as of
15Z, with dewpoints mostly in the 70s across our region.

We expect showers and thunderstorms to blossom in coverage and
intensity across our region as low stratus ceilings continue to
gradually lift, allowing convective temperatures (upper 80s per
the morning sounding at Jacksonville) to be reached by the early
to mid afternoon hours. Abundant tropical moisture and support
aloft from troughing that will be cutting off over our area should
allow for locally heavy downpours to develop, and mesoscale
boundary collisions could support a few storms pulsing and
becoming strong. Stronger storms this afternoon and early this
evening will be capable of producing downburst winds of 40-50 mph,
frequent lightning strikes, and torrential downpours. Weak high
pressure wedging down the southeastern seaboard this afternoon
will generally provide for a west-southwest storm motion, which
will tend to shift convective activity inland towards the I-75
corridor by the late afternoon and early evening hours. Cloud
cover and increasing rainfall chances should keep highs in the
upper 80s to lower 90s, with maximum heat index values remaining
below Heat Advisory levels for the first time in several days, as
values generally peak in the 100-105 range during the early to mid
afternoon.

Convection may linger this evening near the I-75 corridor, with
a few additional showers and possibly a few embedded storms
moving onshore from the Atlantic waters along the I-95 corridor.
Coastal showers and convection may re-ignite along the northeast
FL coast again during the predawn hours as low level northeasterly
flow begins to increase. Meanwhile, the drier air mass currently
positioned north of the Altamaha River will advect slowly
southward into interior portions of southeast GA, where patchy fog
and low stratus clouds may develop during the predawn and early
morning hours on Monday. Lows tonight will remain in the 70s
area-wide.

&&

.SHORT TERM...
(Monday through Tuesday night)
Issued at 150 AM EDT Sun Aug 17 2025

Diffuse frontal boundary will sink slightly further southward on
Monday as a weak ridge of high pressure builds down the
southeastern seaboard and into the area. Very high moisture
content will be in place across the majority of the area through
at least Monday afternoon, however guidance is in good agreement
that uptick in northeasterly flow thanks to the pressure gradient
between ridging in place and Hurricane Erin passing well to the
east will also start to advect some drier air in aloft from
northeast to southwest Monday evening and Night, settling overhead
on Tuesday. The result of this setup will be a fairly sharp
gradient in expected convection/rain chances on Monday, with the
highest POPs being mainly south of I-10 in Florida in the 50-70%
range, and the lowest being from about Waycross northward in the
10-30% range. These chances drop even further on Tuesday, mostly
in the 20-40% range for most of the area with once again the
higher end of the range being areas furthest south and east.

Temperatures will be near normal on Monday, with mostly low 90s
except upper 80s near the coast and St. Johns River. The highest
readings will likely be over interior southeast GA where lower
precip chances and cloud cover will be. After mainly low to mid
70s Monday Night, highs temps will be slightly warmer on Tuesday
with less rain/cloud cover overall as low to mid 90s will be
common area-wide. Similarly, low temps will be just a touch higher
Tuesday Night though still mainly in the low to mid 70s.

&&

.LONG TERM...
(Wednesday through Saturday)
Issued at 150 AM EDT Sun Aug 17 2025

Hurricane Erin will continue to turn north and northeastward away
from the region Wednesday and Thursday, shifting the flow from
onshore/northeasterly towards the south to southwest for the end
of the week and the start of next weekend. Enough dry air looks to
remain in place Wednesday to taper rain chances once again,
however more moist south to southwest flow and an approaching
frontal boundary late in the week is expected to return higher
chances/coverage of showers and t`storms accordingly from Thursday
onward. This front is likely to stall just north of the region,
maintaining a setup featuring plentiful moisture advection south
of the boundary and numerous convection heading into next weekend.
Temperatures overall trend slightly above normal for most or all
of the long term period.

&&

.AVIATION...
(12Z TAFS)
Issued at 821 AM EDT Sun Aug 17 2025

LIFR ceilings will prevail at the Duval County terminals and GNV
through around 13Z. Ceilings should lift to MVFR at CRG and JAX by
14Z, with IFR conditions likely continuing through around 15Z at
VQQ and GNV. MVFR ceilings and at least vicinity showers are
likely to develop at SGJ and SSI by 15Z. Showers and embedded
thunderstorms currently developing over the near shore Atlantic
waters will likely spread onshore by 16Z, with coverage and
intensity then increasing at the Duval County terminals and SGJ
during the early to mid afternoon hours. Convection is expected to
approach GNV towards 20Z. TEMPO groups for brief wind gusts
around 30 knots and IFR conditions during heavier downpours were
placed at each TAF site in northeast FL this afternoon, while
confidence was only high enough for a PROB30 group at this time
for the SSI terminal during the early to mid afternoon hours.
Activity will migrate towards the Interstate 75 corridor by
sunset, with MVFR conditions likely continuing at GNV through
around 02Z tonight. VFR conditions should then prevail at the
regional terminals by 04Z Monday. MVFR visibilities are likely to
develop at VQQ overnight, with lower confidence for showers
redeveloping near the SSI, Duval County, and SGJ terminals during
the predawn hours. Northerly surface winds sustained around 5
knots early this morning will shift to east-northeasterly by 15Z,
with speeds outside of thunderstorm activity increasing to around
10 knots towards 17Z. Surface winds will shift to northeasterly
with diminishing speeds after 23Z.

&&

.MARINE...
Issued at 1133 AM EDT Sun Aug 17 2025

A weak surface trough will linger across our local waters today,
with showers and thunderstorms expected to increase in coverage
and intensity this afternoon. Stronger storms will be capable of
creating briefly strong wind gusts, frequent lightning strikes,
and possible waterspouts. Seas of 2 to 3 feet will prevail both
near shore and offshore through tonight. High pressure will then
strengthen over the Great Lakes region on Monday, with this
feature wedging down the southeastern seaboard through midweek,
resulting in gradually strengthening northeasterly winds across
our local waters. Meanwhile, Major Hurricane Erin will turn
northwestward later today and then northward by Tuesday, remaining
east of northeast of the Bahamas. Easterly swells from Erin will
begin to increase within our local waters on Monday afternoon and
evening, with Small Craft Advisory conditions expected to begin on
Monday night offshore, as seas build to 5-8 feet. Seas near shore
will build to Caution levels of 4-6 feet on Monday night, with
Small Craft Advisory level seas of 5-8 feet developing on Tuesday.
Small Craft conditions continue will through Thursday night as
Erin turns north-northeastward, remaining well offshore of the
U.S. eastern seaboard. Seas will peak in the 8-10 foot range near
shore on Wednesday, with 9-13 foot seas offshore.

Rip Currents / Beach Erosion: Easterly swells of 9-10 seconds will
create a moderate rip current risk at area beaches this afternoon.
Powerful swells emanating from distant Major Hurricane Erin will
arrive at area beaches on Monday afternoon, with swell periods
increasing to 14-16 seconds, with breaker heights building to 3-5
feet for the northeast FL beaches and 2-4 feet at the southeast GA
beaches, creating a high risk for deadly rip currents by Monday
afternoon at all area beaches. Breaker heights will continue to
build on Tuesday, with High Surf Advisory conditions expected at
the northeast FL beaches, as breakers build to 6-8 feet, while
breakers at the southeast GA beaches build to 3-6 feet. Breakers
will peak in the 9-10 foot range at the northeast FL beaches on
Wednesday, with values of 4-7 feet currently forecast for the
southeast GA beaches. Pounding surf and elevated astronomical
tides will likely create at least moderate beach erosion at the
northeast FL beaches towards midweek, especially during the late
afternoon and early evening high tide cycles.

&&

.FIRE WEATHER...
Issued at 1133 AM EDT Sun Aug 17 2025

Northeasterly transport winds around 10 mph will prevail this
afternoon, with breezy surface speeds expected at coastal
locations. Increasing clouds and rainfall / cloud cover should
keep daytime dispersion values generally poor, except low across
north central FL. Transport winds will shift slightly to east-
northeasterly on Monday, with breezy northeasterly surface winds
expected at coastal locations. A drier air mass and higher mixing
heights for locations north of Waycross will yield good daytime
dispersion values, with fair values forecast elsewhere, except
poor across north central FL. Breezy northeasterly surface and
transport winds will then overspread our area by Tuesday
afternoon, creating good daytime dispersion values, with
marginally high values possible for portions of inland northeast
FL, the Suwannee Valley, and north central FL.

&&

.HYDROLOGY / COASTAL FLOODING...
Issued at 1133 AM EDT Sun Aug 17 2025

River flooding...Minor flooding will continue along upper portions
of the Altamaha River through this evening before water levels
fall below flood stage after midnight tonight.

Coastal flooding...latest PETSS and ETSS guidance indicate
inundation up to Minor flood stage possible around high tides
along the Atlantic coast and within the St. Johns River basin
towards midweek, with most locations reaching Action Stage on
Wednesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  90  72  92  71 /  60  30  20   0
SSI  87  77  88  77 /  60  20  20  10
JAX  89  76  91  75 /  80  30  50  10
SGJ  88  76  88  77 /  70  40  60  10
GNV  91  74  91  74 /  80  50  70  10
OCF  90  74  90  74 /  90  50  70  10

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...None.
AM...None.
&&

$$