836 
FXUS62 KJAX 100712
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
312 AM EDT Fri Sep 10 2021

...DRIER TODAY FOR SE GA WITH CONVECTION ACROSS NE FL...

.NEAR TERM [Through Tonight]...

A surface front in the wake of departing post-tropical cyclone 
Mindy will slide across the local area this morning as surface 
high pressure builds northwest to north of the region. In the 
upper levels, a long wave trough extended from New England to 
across the central Gulf Coast states, with embedded mid level 
lobes of PVA tracking across the local area from the WSW. As the 
surface front slides southward across SE GA this morning, a drier,
more stable airmass will prevail into the afternoon under partly 
cloudy skies and breezy onshore flow at the coast. The higher 
rain chances will focus across NE FL where the front will begin to
stall and linger as a wave of low pressure develops across north-
central FL into the afternoon under the deepening upper level 
trough. 

Early this morning, a cluster of showers and storms was edging 
inland from the GOMEX just head of the approaching surface front 
under passing mid level PVA. Through late morning, this convection
will drift eastward across our southern FL zones, with additional
showers or isolated storm possible along the actual surface front
which was shifting south of the GA waters around 3 am. The 
stronger mid level short wave trough fueling the early morning 
storms across the Suwannee River Valley will shift eastward 
through 15-18z, with convection expected to decrease across our 
western zones but increase across our eastern FL zones as upper 
level dynamics phase over the stalling surface front, inducing a 
broad surface low along the boundary across north-central FL into 
the afternoon and early evening hours. Surface convergence near 
this wave of low pressure under a strengthening jet within the 
deepening upper level trough combined with cool 500 mb temps of -8
to -9 deg C will bring the potential for locally heavy rainfall 
and a few strong pulse storms generally after 18z across NE FL 
into the early evening hours especially across the St. Johns 
River basin and toward toward the Atlantic coast. Convection will 
tend to shift WSW through 00z as the surface ridge strengthens 
north and northeast of the region into the evening, shifting the 
broad surface low westward. Strong storms today will have the 
potential today and this evening will have the potential to 
produce gusty winds of 40-60 mph, small hail, locally heavy 
rainfall and frequent lighting. 

Although precipitation will decrease in coverage and intensity
into the evening over inland areas, the lingering trough axis will
serve as a convergent zones tonight which will bring the potential
for showers and isolated storms to coastal areas of NE FL through
the night. 

Temperatures will trend near to just below normal with highs in
the mid to upper 80s inland to the low/mid 80s along the local
coast. Lows tonight will cool into the mid 60s across much of SE
GA under partly cloudy to mostly clear skies and backing ENE
drainage winds. NE FL lows will range in the 70s under lingering
clouds and coastal showers/isolated tstorms. 

.SHORT TERM [Saturday Through Sunday Night]...

A stalled boundary near the Florida / Georgia border will become 
progressively more diffuse and hardly discernible this weekend. 
As a result, north of the front, a slightly cooler and drier air 
mass will prevail across inland portions of southeast GA through
this weekend allowing lows to fall into the mid to upper 60s each
night. The aforementioned weak frontal boundary and deepening 
onshore flow will again develop scattered to numerous mainly 
afternoon and evening convection for locations along and south 
of I-10 on Saturday, with higher areal coverage and intensity 
expected during the late afternoon hours across north central FL 
where dewpoints will be in the lower to mid 70s. Strong storms 
will again be possible for locations south of Gainesville due to 
lingering cool temperatures aloft (-10C, 500 mb) as well as 
mesoscale boundary collisions, which could produce strong
downburst winds as well as localized heavy rain / potential 
flooding due to expected slow storm motion. Highs will generally 
remain in the mid to upper 80s again area-wide, with higher 
humidity values keeping lows in the 70s for most of northeast 
and north central FL.

Upper level troughing will then progress off the U.S. eastern seaboard
by Saturday night, allowing for the massive ridge currently in place
over the Rockies to expand eastward into our region with center 
of ridge over the Mid South extending into Georgia. Consequently, 
there will be a big moisture gradient across the region Sunday 
with precipitable water values across SE Georgia between 1.25 and 
1.50 inches with 1.75 to 2 inches across northeast and north 
central Florida. This change in the weather pattern should allow 
for only isolated to widely scattered afternoon and evening 
convection to develop for locations south of I-10 on Sunday. Our 
local pressure gradient will also loosen as high pressure over the
Carolinas weakens. Highs will climb to the upper 80s to near 90 
for inland locations, while a lingering onshore breeze keeps 
coastal highs mostly in the mid 80s.

.LONG TERM [Monday Through Thursday night]...

Ridging aloft will briefly reside over the SE U.S. early next 
week and will then progress eastward towards midweek,
with deepening southeasterly flow expected towards midweek.
Moisture levels will gradually increase each day, but convective
coverage should be limited to widely scattered early next week,
with less coverage expected across southeast GA. Higher rain
chances will then develop towards midweek as tropical moisture 
overspreads our area from southeast to northwest. Highs early next
week will generally climb to around 90 inland and the mid 80s at 
coastal locations, followed by highs cooling slightly towards 
midweek as cloud cover and convective chances increase. The 
lingering dry and subsident air mass should allow lows to fall to 
the 60s again on Monday night in southeast GA, but 70s will then 
prevail area-wide by midweek as humidity levels climb.

&&

.MARINE...

A front will move south across the local waters this morning then
begin to stall across north-central Florida this afternoon. A wave
of low pressure will form along the surface front this afternoon,
then will shift west across the Gulf of Mexico tonight as high
pressure strengthens northeast of the region. An extended period
of easterly flow is expected Saturday through Tuesday. Elevated
combined seas due to long-period swells will gradually subside
late this weekend. 

Continued Small Craft Advisory headline for the outer today and 
tonight due to marginal combined seas near 7 ft, with a Small 
Craft Exercise Caution headline for the near shore waters due to
combined seas near 6 ft at times. Latest NWPS run was trending
about 1-2 ft at times too high for wave heights based on buoy 
observations, and if this trend continues will update to trend 
more toward the WNA guidance which lowers seas to below SCEC over 
the near shore waters today and has only a brief period of near 7 
ft seas tonight (Fri night) near the Gulf stream for waters south 
of St. Augustine. 

Rip Currents: A high rip current risk will continue for all local
beaches through Saturday due to persistent, long period easterly
swells combined with strengthening onshore flow. Swells dampen
Sunday into Monday, with a moderate rip current risk likely by
early next week.

&&

.HYDROLOGY...

Minor flooding continued along lower portions of the Santa Fe 
River near the Three Rivers Estates gauge. River levels upstream
will rise to action stage during the weekend due to recent 
runoff.

&&

.PREV DISCUSSION [221 AM EDT]...

.AVIATION...
[Through 06Z Saturday]

Prevailing VFR conditions expected through 12z with tempo MVFR at
VQQ due to shallow ground fog. Will also need to monitor inland
progression of early morning convection drifting inland from the
Gulf Coast region which could impact GNV through 12z and at this
time indicated VCSH by 08z. NE winds increase at SSI this morning
trailing an early morning frontal passage. This front is expected
to stall and linger across NE FL this afternoon as a wave of low
pressure develops along the boundary across north-central FL this
afternoon. Showers and storms will increase in coverage and intensity
after 17z across NE FL into the early evening under easterly 
winds. Advertised VCSH BY 16z for NE FL terminals with VCTS by 
16-19z. Easterly winds increase at coastal terminals through the
day today from SSI to SGJ with gusts of 11-13 kts into the early 
evening. Precip coverage will tapper off inland during the early 
evening, but onshore low level flow under a deepening mid/upper 
level trough will continue isentropic lift over the area along the
meandering front along the NE FL coast tonight, which could bring passing
showers or TS to SGJ, CRG and potentially JAX through 06z Saturday.
SREF probabilities suggest the highest potential for MVFR 
ceilings at SGJ this afternoon and evening between 18z-00z.


.FIRE WEATHER...

Breezy westerly surface and transport winds will quickly diminish 
this evening and will shift to northwesterly towards midnight and 
then northerly towards sunrise on Friday. Breezy northeasterly 
surface and transport winds will then develop towards noon at 
coastal locations and will gradually spread inland towards the 
Suwannee Valley. Lighter wind speeds will prevail across inland 
southeast Georgia as well as north central Florida, where low 
daytime dispersion values are expected. Meanwhile, a drier air 
mass will filter into inland portions of southeast Georgia from 
Friday through the weekend, where minimum relative humidity values
will fall to 40-45 percent during the afternoon hours. Breezy 
easterly surface and transport winds will continue across 
northeast Florida this weekend, with lower speeds over north 
central FL resulting in marginally low daytime dispersion values.

&&

.PRELIMINARY POINT TEMPS/POPS...

AMG  86  66  87  65  88 /  10  10  10   0  10 
SSI  84  73  86  75  86 /  10  10  20  10  20 
JAX  86  70  87  73  88 /  30  30  30  10  20 
SGJ  85  74  85  74  86 /  50  50  50  10  30 
GNV  88  71  87  70  88 /  50  40  50  10  30 
OCF  88  71  88  72  89 /  60  50  50  10  30 

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...High Rip Current Risk through late Saturday night for Coastal 
     Duval-Coastal Flagler-Coastal Nassau-Coastal St. Johns.

GA...High Rip Current Risk through late Saturday night for Coastal 
     Camden-Coastal Glynn.

AM...Small Craft Advisory until 7 AM EDT Saturday for Waters from 
     Altamaha Sound GA to Fernandina Beach FL from 20 to 60 NM-
     Waters from Fernandina Beach to St. Augustine FL from 20 to 
     60 NM-Waters from St. Augustine to Flagler Beach FL from 20 
     to 60 NM.

&&