Severe Thunderstorm Warning 206, NWS Jacksonville, FL

Area Forecast Discussion
National Weather Service Jacksonville FL
112 PM EDT Thu Jul 13 2017

...NEAR TERM WARMING TREND WITH LOWER RAIN CHANCES FRIDAY...

.NEAR TERM...Today & Friday...

This afternoon...Deeper ESE flow today compared to yesterday with
a return of higher moisture. PWAT values were almost 0.5 inches
more than 24 hrs ago with JAX at 1.97" this morning per the 12Z
RAOB. This increase in moisture along with diurnal heating created
an earlier start to convection today with scattered showers
popping across the St. Johns River basin by 11 am. The surface
ridge axis extended across SC from a center across the western
Atlantic. This increased subsidence will limit convective growth
across SE GA today, with the highest rain chances expected across
NE FL. As the afternoon progresses, the east coast sea breeze will
continue to press farther inland serving as the main foci for
scattered to numerous showers/tstorms, mainly west of Highway 301
by mid-afternoon, then more toward the I-75 corridor through the
late afternoon and early evening hours. Given the presence of dry
mid level air generally above 615 mb, even drier than yesterday,
the Downdraft CAPE (DCAPE) from the JAX RAOB was over 1000 J/kg.
This index indicates an increased potential in strong wet
downbursts from deeper tstorms, with gusts of 40-60 mph possible.
Thus, a few strong to severe are possible this afternoon and
evening, generally west of Highway 301.

Tonight...Expect a clear evening along the Atlantic coast, and
dry conditions after sunset for most locations as convection
inland near the I-75 corridor fades with loss of heating and
drifts farther west. Given fog and stratus across SE GA this
morning, and that SREF guidance yesterday handled this well,
advertised patchy fog in the forecast for inland SE GA and the
northern Suwannee River Valley tonight. Fog could be locally dense
at times. Low temps will range in the 70s inland to near 80 along
the St. Johns River basin and Atlantic coast due to onshore flow.

Fri...The low level ridge axis will settle farther south across
SE GA. The east coast sea breeze will continue to be dominant with
morning coastal showers possible mainly along the NE FL coast,
then additional convective growth will spread inland through the
day toward I-75, while the east coast clears into the mid
afternoon. Rainfall coverage is expected to be less with drier air
spreading across the area and the increase in low level
subsidence, but this could support some isolated stronger storms
capable of gusty winds. In addition, slower storm motion will
bring locally heavy rainfall to some areas. With less cloud cover
and rising thicknesses, high temperatures will warm into the
mid/upper 90s inland to near 90 coast. Heat index values will near
105 degrees.

.SHORT TERM...Saturday & Sunday...

Sat will be the transition day with the hottest temps across NE
FL as the mean ridge axis shifts farther south over north Florida
and a trough begins to deepen across the eastern CONUS. Drier air
with PWAT values only near 1.5 inches will limit rainfall
potential across NE Florida, while deeper moisture with PWATs
nearing 2 inches filters across SE GA Sat afternoon ahead of the
frontal zone. Both sea breezes will develop and drift inland, with
convergence between I-75 and Highway 301 in the late afternoon.
Saturday high temps will continue to soar into the mid/upper 90s
inland to near 90 coast.

Sun rain chances increase as the frontal boundary edges a bit
farther south and moisture increases from 1.75 to over 2 inch
PWATs across the forecast area under WSW steering flow. Best
coverage of afternoon convection will focus across SE GA, with
more scattered convection across NE FL especially near the St.
Johns River basin in the late afternoon where sea breezes/outflows
will converge. Temperatures will begin to trend slightly cooler
with increase cloud cover with highs in the low/mid 90s.

.LONG TERM...Monday through Thursday...

An unsettled and generally wet pattern is expected next week as
the trough lingers across the Atlantic coast states while the
1000-700 mb ridge axis persists across south-central Florida. This
regime will continue prevailing WSW steering flow and generally
high moisture content streaming over the forecast area with a
dominant west coast sea breeze regime. The GFS started to indicate
a deeper mid/upper level trough axis digging southward across the
eastern Gulf Wed, with a continuation of high moisture across NE
FL and coastal SE GA, but with drier air with PWATs falling below
1.5 inches across our WNW GA zones. For now trended with lower
rain chances Wed across inland SE GA, but above normal rain
chances increase Thu once again as the trough axis shifts westward
as moisture plume lifts back north. Temps will trend near to
slightly above normal with highs in the low/mid 90s and muggy
overnight conditions with lows in the 70s.

&&

.AVIATION...Easterly flow will focus best chances of afternoon TS
at VQQ and GNV with potential MVFR conditions due to rainfall.
Stronger wind gusts in tstorms expected today. Coastal locations
including SSI, CRG and SGJ will have low chance of afternoon/evening
shower, so kept out of 18Z TAFs for now. There is low potential
for any restrictions at terminals most terminals tonight except
for GNV and VQQ where SREF guidance suggested about 12-305
probabilities of MVFR conditions and 10-20% of LIFR conditions.
Given that the SREF performed well yesterday with low stratus
across SE GA, suggested this potential in the 18Z TAFs with SCT005
for both GNV and VQQ after 08Z Friday.

&&

.MARINE...Onshore ESE flow expected through Friday with speeds
generally 10 kts or less with scattered showers and a low chance
of isolated thunderstorms. Combined seas 3-5 ft. Winds will veer
more SSW late Friday through early next week as a frontal zone
stalls north of the waters. Nocturnal SW winds surges will near 15
kts over the outer waters, while nearshore winds will become
onshore with the east coast sea breeze in the afternoon. Thunderstorm
activity will increase next week as well with afternoon and evening
storms drifting offshore each day.

Rip Currents: Moderate risk due to persistent onshore flow and ESE
swells with 10-11 second periods.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  74  96  75  96 /  10  20  10  40
SSI  78  89  77  90 /  10  10   0  20
JAX  75  92  74  95 /  10  20   0  20
SGJ  77  89  76  91 /  10  20   0  10
GNV  74  94  74  95 /  10  30  10  20
OCF  74  93  74  95 /  20  40  10  20

&&

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

Enyedi/Sandrik/Walker

Hazardous Weather Outlook
National Weather Service Jacksonville FL
252 PM EDT Thu Jul 13 2017

AMZ450-452-454-470-472-474-FLZ020>025-030>033-035>038-040-124-125-
GAZ132>136-149>154-162>166-141900-
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-
252 PM EDT Thu Jul 13 2017

...MODERATE RISK OF RIP CURRENTS...

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

.DAY ONE...This Afternoon and Tonight...

Scattered thunderstorms will continue to track west mainly west of
Highway 301 this afternoon and toward the Interstate 75 corridor
through the early evening. A few strong to severe storms will be
capable of producing damaging wind gusts up to 60 mph, excessive
lightning and locally heavy rainfall. Storm motion is to the west-northwest
around 15 mph.

Thunderstorms will track west of I-75 through the early evening
with dry conditions expected the rest of the night. Patchy dense
fog will be possible across inland areas early Friday morning
which could cause local visibilities below a quarter mile.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday...

Isolated thunderstorms are expected Friday and Saturday, then
storms will become more numerous Sunday through Wednesday.
Locally heavy rainfall...gusty winds...and frequent lightning will
be possible in the strongest thunderstorms.

.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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