Area Forecast Discussion
Issued by NWS Jacksonville, FL

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FXUS62 KJAX 221602

Area Forecast Discussion
National Weather Service Jacksonville FL
1202 PM EDT Fri Sep 22 2017


Early afternoon surface analysis depicts high pressure (1022
millibars) centered over the eastern Great Lakes states and
extending southward down the spine of the Appalachians. Major
Hurricane Maria was located about 850 miles to the southeast of
Mayport, FL as of 15Z and was moving northwestward at 8 mph. A
coastal trough was situated over the northeast Florida waters.
Aloft...a trough extending southwestward from weakening Tropical
Storm Jose off New England continues over our region, while a
narrow ridge centered over the eastern Great Lakes extends
southwestward into eastern Texas. The combination of cold and
unstable air aloft (-10 degrees Celsius at 500 millibars per the
12Z sounding at JAX) from the upper trough and the coastal trough
has generated persistent deep convection over the northeast
Florida coastal waters this morning, with outflows from this
activity pushing occasional lighter showers westward into Flagler
and southern St. Johns Counties. Breezy northeasterly winds are
now in place along the coastal counties, with a healthy cumulus
field developing over much of our region. Temperatures at 17Z
were generally climbing into the mid 80s, with dewpoints ranging
from the upper 60s to the mid 70s.

Despite deepening onshore flow and cold, unstable conditions
aloft, deep-layered moisture is lacking over most of our land
zones today (PWATS generally 1.5 inches or less), which should
limit convective coverage this afternoon to widely scattered. The
best chances for showers and thunderstorms this afternoon will be
south of Interstate 10 and also for a small portion of inland
southeast Georgia to the north of Waycross. A few strong storms
containing gusty winds of 40-50 mph, frequent lightning strikes,
and locally heavy rainfall will be possible in these areas as
storms generally move westward around 10 mph. Highs today will
range from the upper 80s well inland to the low/mid 80s at the
coast. A surge of deeper moisture will advect westward from the
Atlantic waters into the coastal counties after midnight tonight,
with increasing chances for showers and thunderstorms during the
predawn hours from the St. Johns River basin eastward.


Periods of MVFR ceilings around 2500 feet will be possible at the
Duval County terminals and SGJ through tonight, with occasional
showers possible through tonight at SGJ. A period of MVFR
conditions will also be possible from 18Z-00Z at GNV as showers
and isolated thunderstorms potentially impact the terminal. MVFR
ceilings are expected to prevail after 06Z at the Duval County
terminals, SGJ, and SSI, with shower coverage increasing during
the predawn hours on Saturday. East-northeasterly surface winds
will be sustained at 10-15 knots at the regional terminals through
00Z, with occasional gusts to 20 knots at SGJ and the Duval County
terminals after 18Z. Surface winds will remain sustained around
10 knots after 00Z at SGJ and SSI.


An east-southeasterly swell originating from Hurricane Maria is
gradually building, with seas in the offshore waters set to reach
Small Craft Advisory levels of 5-7 feet this afternoon. Small
Craft should Exercise Caution in the nearshore waters, where seas
will build to 4-6 feet this afternoon. Small Craft Advisory level
seas of 5-7 feet will likely move into the near shore waters
during the predawn or early morning hours on Saturday. Our local
pressure gradient will tighten on Saturday night as Maria makes
its closest approach to our waters (more than 550 miles east of
Mayport), with east-northeast winds strengthening to caution
levels of 15-20 knots offshore and just under caution levels near
shore. Offshore seas will peak in the 8-11 foot range on Saturday
night and Sunday, with near shore seas peaking at 6-9 feet. Winds
will turn to a more northerly direction and will begin to decrease
by Monday, allowing near shore seas to fall back to caution
levels by Tuesday.

Rip Currents: Moderate risk today as east-southeasterly swells
from Major Hurricane Maria gradually build. High risk will be
needed for all area beaches this weekend and likely early next
week due to high surf and long period swells from Maria.


A Coastal Flood Advisory remains in place through the evening
high tide cycle tonight for the St. Johns River basin, as minor
flooding continues during each high tide cycle from Jacksonville
southward to Palatka, while near moderate flooding continues south
of Palatka into the Welaka and Ocklawaha River basins.
Strengthening onshore winds may keep the risk of minor to moderate
flooding in place during times of high tide into early next week.

Moderate flooding continues along portions of the Santa Fe and St.
Mary`s Rivers, with minor flooding along the Satilla River east of
Waycross and portions of the Upper Suwannee River.


AMG  88  70  87  69 /  30  10  40  10
SSI  82  77  81  74 /  10  30  40  20
JAX  86  73  84  72 /  20  30  50  20
SGJ  83  78  82  74 /  40  30  50  20
GNV  87  71  87  70 /  30  20  50  10
OCF  87  71  87  71 /  40  20  60  10


FL...Coastal Flood Advisory until midnight EDT tonight for Clay-
     Coastal Duval-Flagler-Inland Duval-Putnam-St. Johns.

AM...Small Craft Advisory for hazardous seas until 3 AM EDT Tuesday
     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.



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