Area Forecast Discussion
Issued by NWS Jacksonville, FL

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434
FXUS62 KJAX 171956
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
356 PM EDT Tue Oct 17 2017

...PROLONGED STRONG ONSHORE WIND EVENT WITH HIGH SURF...A HIGH
RISK OF RIP CURRENTS...AND COASTAL FLOODING THROUGH THURSDAY...

.CURRENTLY...
Afternoon surface analysis depicts a cold front decelerating on
its southward push towards Lake Okeechobee, with strong high
pressure (1031 millibars) sprawling over the Tennessee Valley and
Appalachians. Aloft...a broad trough is in place over the eastern
U.S., with an embedded shortwave digging slowly southeastward
through Georgia. A band of heavy showers and embedded
thunderstorms were located over the offshore waters adjacent to
northeast Florida, with a few light showers occasionally sneaking
into far southern Flagler County. A tight pressure gradient
remains in place over our region, with strong onshore
northeasterly winds sustained around 20 mph along the coast, with
occasional gusts of 30-35 mph persisting at area beaches. A much
drier air mass has plunged into inland southeast Georgia and the
northern Suwannee Valley, where temperatures are rising to the
70-75 range with dewpoints in the 40s and 50s. Multi-layered
cloudiness persists over the rest of coastal southeast Georgia,
northeast and north central Florida, with temperatures in upper
60s to lower 70s, with dewpoints generally in the upper 50s to mid
60s.

.NEAR TERM.../THROUGH WEDNESDAY/...
The shortwave over Georgia will continue to slowly pivot
southeastward overnight, and this feature will likely add some
lift and will team up with coastal convergence resulting from deep
onshore flow to increase shower chances overnight over Flagler,
Putnam, and St. Johns Counties. Short-term, high resolution
guidance indicates that these showers will expand in coverage
after midnight tonight, with likely POPS placed in the forecast
grids for most of Flagler County through Wednesday morning. Widely
scattered showers may also begin advecting onshore over the rest
of the coastal counties by the mid to late morning hours on
Wednesday. We expect deeper moisture to remain displaced just to
the south of our area through Wednesday, with mainly light QPF
amounts anticipated. Meanwhile, a seasonably cool and dry air
mass will continue to overspread inland southeast Georgia and the
northern Suwannee Valley. Inland winds will gradually decouple
overnight, with mostly clear skies expected. This weather pattern
will allow lows tonight to fall to the upper 40s near the Altamaha
River, ranging to the mid 50s along inland portions of the I-10
corridor. These values are about 5-8 degrees below mid- October
climo. A tight pressure gradient in place over our region will
keep breezy to occasional windy northeast winds in place for
locations along and east of I-95, setting up a large low
temperature gradient over our area. Coastal lows will generally
range from 65-70, which is a few degrees above climo.

Breezy to windy conditions will prevail for locations along and
east of I-95 on Wednesday, with breezy northeasterly winds
developing over inland northeast and north central Florida by the
mid to late morning hours. The approaching new moon will add an
increasing astronomical component to ongoing tidal flooding along
the Atlantic coast and within the St. Johns River basin (see
Hydrology discussion below). A stratocumulus cloud field will
gradually advect into the inland northeast and north central
Florida counties during the afternoon hours, with mostly sunny
skies and just a few cumulus clouds expected over inland southeast
Georgia. Highs on Wednesday will range from the mid to upper 70s,
except lower 80s for inland north central Florida. These values
are near or perhaps a degree or two below climo.

.SHORT TERM.../WEDNESDAY NIGHT THROUGH FRIDAY/...
High Pressure will remain anchored over the Mid Atlc/Carolinas
through the period with the old cold frontal boundary well south
of the region over the Southern FL Peninsula. The pressure
gradient between the two features will slowly weaken through the
period but the E to NE steering flow will remain in place and will
continue at least breezy conditions along the coast with NE sfc
winds at 15-25G30-35 mph at times along with scattered coastal
showers pushing into the I-95 corridor at times. Some locally
heavy rainfall appears possible along the NE FL coast south of
Jacksonville but does not appear to be organized enough that it
will warrant a Flood Watch. The onshore flow along with the
approach of the New Moon on the 19th will continue Minor Coastal
Flooding along the coast and down the St Johns River Basin and
expect Coastal Flood Advisories to continue through this period.
Temps will remain closer to normal with Lows in the 50s/60s inland
and near 70 along the coast while Highs will rebound back into the
lower 80s due to onshore flow from the warmer waters and possibly
reaching the Mid 80s over far inland areas. Much of inland NE FL
and inland SE GA will remain dry through this period with light NE
sfc winds at 10-15G20-25 mph at times during the afternoon hours.

.LONG TERM.../SATURDAY-TUESDAY/...
Sat...Lingering easterly flow will continue with breezy conds
along the coast and coastal showers remaining possible at times.
Temps back above normal with highs into the lower/middle 80s.

Sun/Mon...Steering flow will shift to the south ahead of the next
trof and expect deeper moisture assocd with the old frontal
boundary will lift back northward and this will lead to much
better rain chances area-wide with scattered to numerous showers
mainly diurnal in nature along with an isolated thunderstorm
possible at times. Temps remain above normal with highs into the
middle 80s and lows in the 60s/lower 70s.

Tue...Long-range models still trying to come together with next
significant cold frontal passage with timing and amount of
shower/storm activity and for now still have low confidence in
details. But some shower/storm activity will be possible in this
time frame before much cooler/drier airmass filters in the rest of
the week.

&&

.AVIATION...
MVFR ceilings of 2000-2500 feet are expected to prevail through
around 00Z at the regional terminals. Ceilings tonight should
rise into the VFR range, generally 3000-4000 feet. Sustained
northeasterly surface winds will generally be around 15 knots late
this afternoon, with frequent gusts of 20-30 knots expected at
the regional terminals. Speeds will remain elevated overnight at
SGJ, with sustained speeds around 20 knots and generally 10-15
knots elsewhere, except 5-10 knots at VQQ and GNV. Showers may
begin to impact SGJ towards 12Z, with MVFR ceilings of 2000-3000
feet expected to redevelop at SGJ towards sunrise. Gusty
northeasterly surface winds will also redevelop shortly after
sunrise at each terminal.

&&

.MARINE...
A tight pressure gradient will prevail over our region into the
upcoming weekend as high pressure remains situated to the north of
our region and the cold front that pushed through the coastal
waters last evening stalls over south Florida. Northeasterly winds
of 20-25 knots with occasional gusts to Gale Force will prevail
through Wednesday night, with Small Craft Advisories posted for
all area waters. Near shore seas of 6-9 feet are expected through
Wednesday afternoon, and seas offshore peaking this afternoon in
the 8-11 foot range and will then gradually decrease back to 6-9
feet by Wednesday night and Thursday. Onshore winds may fall back
to caution levels of 15-20 knots by Thursday, but seas offshore
will likely remain in the Small Craft Advisory range throughout
the weekend, with seas near shore falling back to caution levels
of 4-6 feet by Thursday and remaining elevated through the
weekend.

Rip Currents: High risk to continue through at least Wednesday,
with breakers of 5-7 feet at area beaches also continuing through
Wednesday and minor beach erosion possible during times of high
tide.

&&

.HYDROLOGY...
Elevated water levels that were in place from onshore winds this
weekend in the St. Johns River Basin have been elevated further by
the northeasterly wind surge last night. In addition, the upcoming
new moon will add a few tenths of a foot to the water levels
beginning on Wednesday. Tide gauges along the St. Johns and
Flagler County coasts are approaching moderate flood levels
during high tide, with coastal levels reaching action stage at
Mayport, Fernandina Beach, and Cumberland Island. The astronomical
cycle associated with the new moon will likely bring water levels
into minor flood status on Wednesday along the Nassau,Camden, and
Glynn coasts on Wednesday morning, and a Coastal Flood Advisory
will go into effect beginning at 5 AM Wednesday. Gauges along the
St. Johns River from downtown Jacksonville southward through
Putnam County are close to reaching moderate flood levels during
high tide on Wednesday, so a coastal flood warning will likely be
issued for the St. Johns Basin this evening or overnight to
replace the advisory currently in place.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  49  77  56  82 /   0   0   0   0
SSI  64  76  66  79 /  10  30  30  30
JAX  60  77  64  81 /  10  30  20  30
SGJ  69  78  70  81 /  30  40  40  50
GNV  62  81  63  84 /  10  10  10  20
OCF  64  82  65  85 /  10  20  10  30

&&

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

     Coastal Flood Advisory from 5 AM Wednesday to 11 AM EDT Thursday
     for Coastal Nassau.

     Coastal Flood Advisory until 7 PM EDT Thursday for Clay-Coastal
     Duval-Flagler-Inland Duval-Putnam-St. Johns.

     High Surf Advisory until 7 PM EDT Wednesday for Coastal Duval-
     Coastal Nassau-Flagler-St. Johns.

GA...High Rip Current Risk through Wednesday evening for Coastal
     Camden-Coastal Glynn.

     Coastal Flood Advisory from 5 AM Wednesday to 11 AM EDT Thursday
     for Coastal Camden-Coastal Glynn.

AM...Small Craft Advisory until 6 AM EDT Friday 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.

     Small Craft Advisory until 10 PM EDT Wednesday for Coastal
     waters from Altamaha Sound to Fernandina Beach FL out 20 NM-
     Coastal waters from Fernandina Beach to St. Augustine FL
     out 20 NM-Coastal waters from St. Augustine to Flagler
     Beach FL out 20 NM.

&&

$$

Nelson/Hess/Corless



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