Special Weather Statement, NWS Jacksonville, FL

Area Forecast Discussion
National Weather Service Jacksonville FL
357 PM EDT Tue Aug 8 2017

.CURRENTLY...
Afternoon surface analysis depicts Atlantic high pressure (1022
millibars) centered near Bermuda, with its axis extending across
central Florida. A cold front was pushing slowly southward through
the coastal Carolinas and into central, with high pressure (1024
millibars) blanketing the upper Midwest. Aloft...deep-layered
ridging over the central Atlantic Ocean extends westward across
the Florida peninsula, while a broad trough is in place from the
northern Rockies southeastward through the Upper Midwest, Great
Lakes States, and the northeastern U.S. A few shortwave troughs
are embedded within west-southwesterly flow that extends from
coastal Texas across the deep South. Scattered convection has
developed along the Atlantic sea breeze, which has been mostly
pinned to the east of I-95. Southwesterly steering flow has
carried a few thunderstorms into the near shore coastal waters,
with a funnel cloud being reported earlier just east of the
Intracoastal Waterway near Nocatee. Convection is increasing in
coverage over the Okefenokee Swamp closer to the shortwave energy
within the deeper southwesterly flow, with sparse coverage so far
along the Gulf coast sea breeze in the Suwannee Valley. Outside of
convection, temperatures inland are generally in the lower 90s,
with coastal temperatures dropping back into the mid and upper 80s
due to the passage of the sea breeze. Dewpoints are generally in
the mid to upper 70s.

.NEAR TERM (This Afternoon through Wednesday)...
Outflows and sea breeze boundaries should merge during the late
afternoon and early evening hours in between the U.S. 301 corridor
and I-95, with a west-southwesterly steering flow bringing
convection back into coastal locations towards or shortly after
sunset. Likely POPs were placed in the forecast grids for these
areas, with scattered coverage elsewhere. Storms may pulse into
the strong to marginally severe category through early evening,
with damaging wind gusts of 40-60 mph, frequent lightning, and
localized flooding as storms tend to back-build or train over the
same locations. Short-term, high resolution guidance indicates
that shortwave energy moving east-northeastward along the frontal
surface in south central Georgia will spark a couple of additional
rounds of convection during the mid to late evening hours that
should progress quickly eastward. We have left likely POPs over
coastal southeast Georgia through midnight, with scattered POPs
continuing through around midnight along much of the I-95 corridor
and a good portion of inland southeast Georgia. Convection should
then finally depart into the coastal waters shortly after
midnight. Plenty of cloud cover and a warm south-southwesterly
flow will keep lows in the mid 70s inland to near 80 at area
beaches.

Wednesday will be a transition day in our weather pattern as the
frontal boundary approaching the Altamaha River from the north
stalls and the 1000-500 millibar ridge axis slowly lifts
northward towards the I-10 corridor late in the day. A very loose
pressure gradient will essentially allow the surface ridge that
will be moving eastward towards the Mid-Atlantic region to bridge
the front, while a mostly westerly flow prevails aloft. Deep
moisture will continue to reside over our region to the south of
the frontal boundary, while drier air associated with the deep-
layered ridge attempts to move into north central Florida from the
south late in the day. Winds will become light and onshore early
in the day, with scattered thunderstorms expected to develop along
the I-95 corridor and points eastward by the late morning hours.
Outflows and sea breeze boundaries will likely collide along or
just west of the U.S. 301 corridor during the afternoon hours.
Likely to categorical POPs were used for most areas west of I-95
during the afternoon hours. Very light steering flow will equate
to slow moving convection, with the potential for localized
flooding expected to be greater than the past few days. WPC
currently highlights our northern Georgia counties within a
marginal risk for excessive rainfall, where the added influence of
the nearby frontal boundary may keep convection going well into
the evening hours for inland locations. Onshore winds developing
during the morning hours will keep coastal highs in the mid to
upper 80s, with lower 90s expected for most inland locations
before convection develops.

.SHORT TERM (Thursday through Friday...
A fairly weak pressure pattern will be across the local forecast
area with weak ridging aloft and low level troughs meandering
across the local forecast area. One trough axis is expected to
stall and meander along the SE Atlantic seaboard including SE GA,
while another surface trough axis in the form of a tropical wave
will move across south Florida late Thu. Both of these features
will drift westward late Thu into Fri as a surface ridge begins to
build across south Florida. These garbled surface synoptic
features will bring fairly light and varied wind directions until
the sea breeze circulations set-up each day, which will likely
occur by midday as high temps warm into the low/mid 90s inland.
Indicated scattered 30-50% rain chances Thu for inland areas where
sea breezes merge because although airmass will be saturated,
weak upper level pressure pattern under mean layer ridge axis
would tend to suppress deep convective growth. Fri trended back
above normal for rain chances as the ridge axis breaks down and
high moisture and diurnal instability will remain high. Convection
will decrease each evening with loss of heating through midnight,
with only a low chance of a precip after midnight through sunrise
mainly across SE GA near weak and diffuse low level trough. Min
temps will range in the 70s under partly to mostly cloudy skies.

.LONG TERM (Saturday through Tuesday)...
Synopsis: Will be monitoring a tropical area of low pressure as it
drifts west toward the Bahamas during the later half of the
weekend. Currently the National Hurricane Center indicated a 30%
chance of tropical cyclone development over the next 5 days. Both
the GFS40 and ECMWF indicated the surface low drifting toward the
Bahamas early next week, but the models diverge with the structure
and intensity of the low as it begins to interact with the
deepening upper level trough across the eastern CONUS. At this
time, based on the latest forecast model guidance, an increase in
rip currents along the local coast next week is the main impact
from this system. Locally, daily sea breeze storms are expected
with a continuation of muggy and seasonably warm temperatures.

Sat & Sun...Mean layer 1000-500 mb SSW steering flow will be weak
10 kt or less across the area between the Bermuda-Azores high
pressure ridge axis settling southward from north-central FL Sat
to across south FL Sun as a trough axis begins to deepen over
Great Lakes and TN River Valley. This steering pattern combined
with high atmospheric moisture content (PWATs 2-2.25 inches per
the GFS40) will fuel scattered to numerous daily sea breeze
induced showers and tstorms. Light steering flow will enable both
the Gulf Coast and Atlantic Coast sea breezes to develop by early
afternoon with convection drawn inland toward the diurnal thermal
trough into the afternoon as high temps rise into the lower 90s. A
few strong storms capable of gusty wet downbursts will be possible
as well as locally heavy rainfall each day with the peak in
convective intensity late afternoon and early evening across
inland areas generally between I-75 and the St. Johns River basin.
Muggy conditions will continue overnight with a gradual decrease
in convective after sunset with min temps ranging into the 70s.

Mon & Tue...Stronger SW flow develops as the trough axis deepens
across the region with a stronger west coast sea breeze expected
under a continued moist airmass (PWATs 1.9-2.2 inches). Diurnally
driven convection will blossom across both the Suwannee River
Valley by late morning/early afternoon due to WSW flow, but also
across inland SE GA near trough axis. Precip will further blossom
with diurnal heating each day, with activity advancing toward the
Atlantic coast into the afternoon/evening. The potential for
isolated strong to severe storms will increase this period
especially across SE GA where stronger forcing will reside near
the upper level trough axis. High temps will rise into the 90s
with mins ranging in the 70s.

&&

.AVIATION...
Showers and thunderstorms will impact the terminals periodically
through around 03Z, with gusty winds up to 30 knots and periods
of IFR visibility during heavier activity. Another round of
thunderstorms is possible after 03Z at SSI, with VFR conditions
otherwise prevailing after 03Z at the northeast Florida terminals.
Showers and a few thunderstorms may develop towards 15Z on
Wednesday at the coastal terminals.

&&

.MARINE...
Atlantic ridging extends across central Florida, with a cold front
making slow progress southward through the Carolinas and north
Georgia. South-southwesterly surface winds of 10 to 15 knots
currently prevail over the coastal waters. Our local pressure
gradient will remain loose enough to allow the Atlantic sea breeze
to develop over the near shore waters early this afternoon.
Showers and thunderstorms are expected to impact portions of
mainly the near shore waters late this afternoon and this evening,
with activity potentially impacting the offshore waters from this
evening through the overnight hours. Outside of evening
thunderstorm activity, we expect a southwesterly wind surge to
bring sustained speeds up to near caution levels in the offshore
waters for a brief period of time before gradually relaxing after
midnight. The cold front will stall just north of our Georgia
waters on Wednesday, with a prevailing light southeasterly wind
flow developing and continuing through the upcoming weekend as the
front lifts northward and weak high pressure remains in place
locally.

Rip Currents: A lingering easterly ocean swell will create a low-
end moderate risk at the northeast Florida beaches this afternoon.

&&

.FIRE WEATHER...Low daytime dispersion 15-20 units expected
through Thu due to very weak transport winds of 5-10 mph.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  74  89  74  90 /  30  70  40  50
SSI  80  85  77  86 /  60  40  40  20
JAX  74  90  76  90 /  60  50  30  30
SGJ  78  88  77  88 /  60  40  20  20
GNV  73  93  75  91 /  40  60  40  50
OCF  74  92  75  92 /  40  60  40  50

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...None.
AM...None.
&&

Nelson/Enyedi/Elsenheimer

Hazardous Weather Outlook
National Weather Service Jacksonville FL
428 AM EDT Tue Aug 8 2017

AMZ450-452-454-470-472-474-FLZ020>025-030>033-035>038-040-124-125-
GAZ132>136-149>154-162>166-090830-
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-
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-
Hamilton-Suwannee-Columbia-Baker-Inland Nassau-Inland Duval-Union-
Bradford-Clay-St. Johns-Gilchrist-Alachua-Putnam-Flagler-Marion-
Coastal Nassau-Coastal Duval-Coffee-Jeff Davis-Bacon-Appling-
Wayne-Atkinson-Ware-Pierce-Brantley-Inland Glynn-Coastal Glynn-
Echols-Clinch-Charlton-Inland Camden-Coastal Camden-
428 AM EDT Tue Aug 8 2017

...STRONG THUNDERSTORMS POSSIBLE THIS AFTERNOON AND EARLY EVENING WITH
LOCALLY HEAVY RAIN AND GUSTY WINDS...
...MODERATE RISK OF RIP CURRENTS AT AREA BEACHES...

This Hazardous Weather Outlook is for Northeast Florida,
Southeast Georgia and the Adjacent Coastal Waters.

.DAY ONE...Today and Tonight...

Scattered to numerous thunderstorms are expected to develop
during the mid to late afternoon mainly across the inland areas
although a few storms may make it to the coast this evening before
fading. A few storms may become strong and produce strong gusty
winds in addition to frequent lightning. Locally heavy rainfall
may cause temporary flooding in low lying areas.

There is a Moderate Risk of rip currents at the northeast
Florida beaches due to easterly swells.

A River Flood warning is in effect for the St. Marys River at
Macclenny where minor flooding will occur.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday...

Scattered mainly afternoon and evening thunderstorms are expected
each day. A few strong storms will be possible.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed.

For additional information, visit the National Weather Service in
Jacksonville website on the internet at weather.gov/jax.

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