Area Forecast Discussion
Issued by NWS Jacksonville, FL

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FXUS62 KJAX 182006

Area Forecast Discussion
National Weather Service Jacksonville FL
406 PM EDT Wed Oct 18 2017

Afternoon surface analysis depicts strong high pressure (1031
millibars) centered over the Carolinas and Virginia. The cold
front that passed through our region on Monday night remains
stalled over southern Florida. Aloft...a broad low to mid level
trough over our region is beginning to move offshore, with
ridging amplifying over the western Gulf of Mexico. A tight
pressure gradient prevails over our region, with windy conditions
prevailing along the coast and breezy northeasterly winds over
inland portions of northeast Florida. Fair skies prevail over
inland southeast Georgia, where temperatures have climbed into the
upper 70s with comfortable dewpoints in the 50s. Convergent
onshore winds have advected a cumulus and stratocumulus cloud
field over northeast and north central Florida, with a weak
trough over the coastal waters combining with the departing trough
aloft to generate scattered showers that are migrating into the
near shore waters. Temperatures in northeast and north central
Florida were generally in the 75-80 range with dewpoints in the

Ridging aloft will continue to amplify over the western and
central Gulf of Mexico, while surface high pressure moves only
slowly northeastward over the Mid-Atlantic states while gradually
weakening. This weather pattern will maintain a northeasterly flow
from the surface up through about 10,000 feet over our region,
with flow above that veering to northwesterly. Weak coastal
troughs will migrate onshore over coastal southeast Georgia and
northeast Florida through early Thursday afternoon, bringing
periods of scattered showers to locations east of the U.S. Highway
301 corridor. Activity will remain low-topped and generally brief
in nature tonight, with short-term, high resolution models
targeting coastal Camden, Nassau and Duval Counties with the best
chances for measurable rainfall overnight. Low level flow will
veer to a more easterly direction over southeast Georgia
overnight, which will shut off cool air advection. However,
radiational cooling conditions are expected inland later tonight,
with lows over inland southeast Georgia and the northern Suwannee
Valley falling to the 55-60 range. Lows elsewhere over inland
northeast and north central Florida will fall to 60-65, with
breezy onshore winds keeping lows for locations east of I-95 in
the upper 60s to lower 70s.

Our local pressure gradient will loosen slightly on Thursday, but
near windy conditions will prevail in coastal locations and breezy
conditions will redevelop over inland northeast and north central
Florida during the late morning and afternoon hours. Drier air
will push southward into southeast Georgia on the heels of the
northwesterly flow pattern aloft, which should keep scattered
showers mostly confined to coastal northeast Florida. A few
showers may move inland past the U.S. Highway 301 corridor during
the afternoon hours. Highs will climb back above normal as heights
aloft rise, with low to mid 80s expected inland, with onshore
winds keeping coastal highs in the upper 70s to near 80.

Thursday night through Saturday night...Large and strong surface
high to the north will gradually shift east off the east coast by
Saturday. Breezy northeast winds will continue as the pressure
gradient remains tight. Isolated to scattered showers along the ne
Fl coast will develop north and affect the Ga coast as winds
become more east to southeast Saturday and Saturday night.

A return flow will bring warmer and more humid conditions
starting Sunday as an approaching vigorous trough approaches the
lower Ms river valley from the west. A more unstable airmass will
result in scattered to numerous showers and thunderstorms Sunday
and Monday. Storms may become strong to severe Monday afternoon
into Monday night as vertical shear increases with upper shortwave
trough and associated cold front to the west. Models indicate a
deepening surface low near the central Gulf region Monday...moving
into the ne U.S. on Tuesday. Models similar in moving upper
trough and frontal boundary across the area early Tuesday morning
with drier and cooler air spreading across se Ga/ne Fl. Surface
high pressure will build into the southern plains which will
produce breezy offshore winds and cool conditions through
Wednesday with temperatures at or below average.


MVFR ceilings around 1500 feet are expected at SSI through at
least 06Z, with occasional MVFR ceilings around 2500 feet possible
at the Duval County terminals. Showers are expected to move
onshore into Duval County towards 00Z, with periods of ceilings
around 2000 feet possible at the Duval County terminals during
the evening and overnight hours. Otherwise, VFR conditions will
prevail. Gusty northeasterly winds are expected through 00Z at the
regional terminals, with sustained surface speeds near 20 knots
at SGJ and around 15 knots elsewhere, with frequent gusts of 20-30
knots possible. Winds will decrease after 00Z, but will remain
breezy at SGJ and SSI.


Strong high pressure will remain centered to the north of our
region through the upcoming weekend, keeping a tight pressure
gradient in place over our region. Small Craft Advisory conditions
will continue through Thursday morning over the near shore waters
and through at least Thursday night offshore. Seas of 5-7 feet
will prevail near shore, with 6-9 foot seas prevailing through at
least Thursday afternoon offshore. Small Craft will need to
exercise Caution in the near shore waters on Thursday, as
northeasterly winds will remain in the 15-20 knot range with seas
of 4-6 feet. Winds and seas will remain at caution levels near
shore through the weekend, and seas offshore may remain at SCA
levels past Thursday night into the weekend. A strong cold front
will approach our region from the west by late Monday, with
winds becoming southerly by Monday afternoon. Showers and
thunderstorms should overspread area waters by Monday night along
the front.

Rip Currents/High Surf: High risk of rip currents continues
through Thursday at area beaches. Breaker heights of 5-7 feet will
continue this afternoon, with the High Surf Advisory set to expire
at 7 PM this evening.


The coastal flood warning has been extended into Duval County, as
tide gauges in downtown Jacksonville and on surrounding
tributaries within the St. Johns Basin reached moderate flood
levels during the morning high tide. Strong onshore winds and the
approach of the new moon will keep water levels elevated during
the next several days. A coastal flood advisory continues for
Nassau, Camden, and Glynn Counties through at least Thursday
morning, with minor coastal flooding expected along the beaches.
The coastal flood warning is in effect for the St. Johns Basin
through at least Thursday morning, with moderate flooding also
occurring along coastal St. Johns and Flagler Counties during
times of high tide.


AMG  56  82  55  82 /   0  10   0   0
SSI  67  79  67  80 /  30  10  10  10
JAX  63  80  66  81 /  40  20  10  20
SGJ  72  81  70  81 /  30  40  20  20
GNV  63  84  64  85 /  10  20  10  10
OCF  64  84  65  86 /  10  20  10  20


FL...High Rip Current Risk through Thursday evening for Coastal Duval-
     Coastal Nassau-Flagler-St. Johns.

     Coastal Flood Advisory until 11 AM EDT Thursday for Coastal

     Coastal Flood Warning until 11 AM EDT Thursday for Clay-Coastal
     Duval-Flagler-Inland Duval-Putnam-St. Johns.

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

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

     Coastal Flood Advisory until 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 9 AM EDT Thursday 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.



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