Area Forecast Discussion
Issued by NWS Jacksonville, FL

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FXUS62 KJAX 230944
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
435 AM EST Thu Nov 23 2017

...HEAVY RAINFALL OVER NORTHEAST FLORIDA TODAY...
...STRONG STORMS POSSIBLE IN NORTH CENTRAL FLORIDA...

.CURRENTLY...
Early morning surface analysis depicts low pressure (1012 millibars)
centered over the northeastern Gulf of Mexico. A developing warm
front was pushing northward into north central Florida. High
pressure (1026 millibars) extends from the Ohio and Tennessee
Valleys to the Arklatex region. Aloft...a sharp trough over the
central Gulf of Mexico was progressing slowly eastward, creating
deepening southwesterly flow aloft over our region. Shortwave energy
embedded within this deep southwesterly flow are combining with
strengthening isentropic lift along and north of the warm front have
pushed mostly stratiform rains over most of our region, with a few
convective cells developing along the warm front and moving into
southwestern Marion County as of 0930Z. Temperatures and dewpoints
as of 09Z ranged from the 55-60 over inland southeast Georgia to the
mid/upper 60s over coastal northeast Florida.

.NEAR TERM /Today and Tonight/...
A jet streak rounding the base of the sharp trough over the Gulf of
Mexico will place our region within the divergent right rear
quadrant of this feature from this morning through early this
afternoon. These dynamics, in combination with strengthening
isentropic lift along and north of a warm front positioned over
north central Florida with result in widespread moderate to heavy
rainfall over north central and northeast Florida today, with
embedded thunderstorms expected to develop this morning for
locations south of Interstate 10. Short-term, high resolution
guidance suggests that the highest convective potential will exist
to the south and east of a line from Gainesville to St. Augustine,
or basically where we expect a surface low to track later this
afternoon.

A few rotating supercells may develop within the warm sector over
Marion, southern Putnam and Flagler Counties. The Storm Prediction
Center has indicated a marginal risk for severe thunderstorm
development in north central Florida, and the latest 06Z NAM
operational model indicates that a highly veered low level wind
field will move into these locations shortly after sunrise. The main
threats within any isolated supercells that develop in north central
Florida today would be damaging wind gusts, hail, and a possible
rogue tornado. We expect waves of moderate to heavy rainfall to
overspread the rest of northeast Florida during the early morning
hours, with rainfall amounts by this evening of 1.5 to 3.5 inches
for most locations to the south of Interstate 10. Model soundings
indicate that a drier air mass above 900 millibars (3000 feet) will
filter into southeast Georgia this afternoon as the surface low
pressure center moves onshore along the Florida Big Bend coast, with
rainfall intensity quickly decreasing this afternoon and limiting
rainfall totals generally to the quarter to half inch range for most
inland locations, with half inch to inch totals expected along the
coastal counties of southeast Georgia. Highs over southeast Georgia
will only climb to the lower 60s, with mid 60s along the I-10
corridor, ranging to near 70 in north central Florida.

Our local pressure gradient will tighten late this afternoon as low
pressure emerges into the Atlantic waters, with breezy north
northeasterly winds developing this afternoon and continuing
overnight along and east of I-95. Low stratus clouds will envelop
most of our region overnight, but drying aloft should result in a
shrinking area of showers from northwest to southeast as the night
progresses. Likely POPS will continue for most of the night along
and east of I-95, but convection will move offshore of Flagler
County by early evening as low pressure begins to accelerate away
from our area. Northerly winds in the wake of the departing low
pressure center will usher a cooler air mass into inland southeast
Georgia, where lows will fall to the 45-50 range by sunrise on
Friday. Lows elsewhere will fall into the 50s.

.SHORT TERM.../FRIDAY-SATURDAY/...
Fairly sharp mid-upper level trough across the area early Friday
will move offshore and dampen out as additional shortwave energy
moves into the TN valley Friday night and Saturday. The associated
frontal system and sfc low that are affecting the local area today
will be moving offshore of the southeast U.S. coast on Friday and
Friday night while sfc high pressure moves in from the northwest. As
a result...drier and cooler air will begin moving from northwest to
southeast through Friday with all rains likely moving out late
Friday. The GFS and NAM are dissimilar on Friday with details of the
sfc low and winds off the southeast U.S. coast but GFS likely more
realistic than NAM but used a basic blend of guidance. We advertised
chance of showers for southeast zones early Friday at 30-50 percent
and dropping down to 30 percent or less in the aftn confined to
mainly along the northeast FL coast. A breezy north to northeast
flow expected along the coast and skies should gradually improve
from north to south. Highs should be below normal in the 60s to near
70. Seasonably cool temps Friday night in the mid 40s to around 50.
Saturday...weak high pressure will move in from the west with light
winds and mostly sunny skies except for increasing high clouds as a
shortwave approaches from the west-northwest. Temps expected to rise
to near normal in the upper 60s and around 70. Saturday night...Mid
level shortwave trough will push through the area and an associated
weak reinforcing cold front will push into southeast GA. Only a
period of partly cloudy skies and slight wind shift expected
overnight.

.LONG TERM.../SUNDAY-WEDNESDAY/...
Weak cold front will move south of the area Sunday while sfc high
pressure across the Mid MS Valley pushes east. High Pressure will
move to NC Monday and offshore Tuesday allowing winds to veer and
temps to gradually modify. High pressure ridge will extend west
across the area from the Atlantic on Wednesday. Cool high temps
expected Sunday and Monday slightly below normal but Monday morning
min temps coldest of the mornings around 40-45 inland and upper 40s
near the coast. Temps will warm gradually through mid week. Only a
few showers possible late Tuesday and Wednesday due to onshore flow
and weak coastal trough. Best chance of a shower would likely be
along the coastal counties and marine waters.

&&

.AVIATION...
IFR ceilings will prevail at GNV through at least 15Z, with heavier
rainfall and potential embedded thunderstorms likely resulting in
prevailing IFR visibilities from 10Z-15Z. MVFR visibilities and
light rainfall should overspread SGJ by 10Z, with heavier rainfall
and potential embedded thunderstorms likely from 13Z-18Z. IFR
ceilings should overspread the Duval County terminals by 11Z, with
periods of IFR visibilities during heavier rainfall from 12Z through
around 18Z. IFR visibilities and light rainfall should reach SSI by
13Z. Surface winds around 10 knots with strengthen to 15-20 knots at
SGJ and SSI after 15Z, with sustained winds of 10-15 knots
elsewhere. IFR or LIFR ceilings are expected region-wide by 00Z.

&&

.MARINE...
Low pressure over the eastern Gulf of Mexico early this morning will
move east-northeastward across north central Florida this afternoon,
emerging into the Atlantic waters early this evening.
This low pressure will then gradually strengthen as it accelerates
northeastward off the southeastern seaboard. Our local pressure
gradient will tighten quickly this morning as the low pressure
center approaches the Florida Nature Coast, with northeasterly winds
strengthening to Small Craft Advisory (SCA) levels of 20-25 knots by
the late morning hours. Occasional gusts to Gale Force will be
possible late this afternoon and evening, mainly over the offshore
waters. Seas in the offshore waters will build to 6-8 feet later
this afternoon, with near shore seas peaking in the 5-7 foot range
from late this afternoon through early Friday morning. Winds will
shift to a northerly direction by late this evening, and offshore
seas will peak tonight in the 6-9 foot range. Winds and seas will
fall back to caution levels in the near shore waters during the late
morning hours on Friday, with seas remaining at SCA levels through
early Friday evening. Weak high pressure will then build into our
area Friday night and Saturday. Seas will remain at caution levels
of 4-6 feet on Friday night, with headlines not expected this
weekend as a stronger high pressure center builds to the north of
our region, resulting in some enhancement to northeasterly winds by
Sunday.

Rip Currents: Moderate risk expected through the weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  60  47  64  43 /  60  40  20  10
SSI  63  51  63  49 /  80  70  30  10
JAX  65  55  65  47 /  90  80  40  10
SGJ  68  58  67  52 / 100  80  50  10
GNV  67  56  67  47 /  90  70  30  10
OCF  68  58  70  49 /  90  70  40  10

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...None.
AM...Small Craft Advisory from 9 AM this morning to 10 PM EST 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 from 10 AM this morning to 10 AM EST Friday
     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/Shashy



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