Area Forecast Discussion
Issued by NWS Jacksonville, FL

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FXUS62 KJAX 270657

Area Forecast Discussion
National Weather Service Jacksonville FL
257 AM EDT Tue Jul 27 2021

.NEAR TERM [Through Tonight]...

Pre-dawn hours...
A weak surface low was located over Glynn County Georgia this morning
and will make a very slow drift toward northward across southeast
Georgia this morning. Surface based convergence is indicated
along the Georgia coast and coastal plains of Georgia where the
best rainfall and instability resides with embedded convection
continues particularly near the the mouth of the Altamaha River
Basin. Across the Suwannee Valley some isolated convection is
occurring with showers extending into Alachua County. During the
remaining pre-dawn hours isolated to scattered showers will
continue across Southeast Georgia and Northeast Florida with a
prevailing southwesterly flow with abundant tropical moisture with
precipitable water values in the 2.1 to 2.4 inch range.

Elevated rain chances with a remnant and wake trough axis across
SE GA and near the I-10 corridor of NE FL brining the potential
for locally heavy, potentially flooding rainfall. The Excessive
Rainfall Outlook from WPC still has SE GA to a Slight Risk for
today. The low will continue to drift toward Savannah, potentially
towards the South Carolina coast, but remaining in a weakened
state. At the same time, subtropical ridge from the Atlantic will
extend west across the south-central Florida peninsula and into
the eastern Gulf. With the ridge axis to the south, a southwest
flow regime will prevail across the region. This pattern will
support scattered showers and storms over the Gulf waters and
along west coast of Florida during the early morning hours, with
the convection then shifting east over the Suwannee Valley and
interior southeast Georgia by late morning and increasing in areal
coverage east of highway 301 toward the coast each afternoon and
early evening along the sea breeze boundaries where the highest
rain chances (Pops 50- 70%) will reside. Locally heavy rain and
localized minor flooding in addition to localized strong gusts and
frequent lightning. Southwest flow will aid in very warm
temperatures reaching the low to mid 90s, with much higher
moisture leading to head indices of 101 to 106 degrees.

With the loss of daytime heating, showers and thunderstorms will
gradually subside to scattered in areal coverage this evening
with numerous showers and storms mainly confined to the coastal
areas during the early to mid evening. During the pre-dawn hours
early start to activity along the Big Bend is expected, with some
showers spilling into the north central Florida and Suwannee
Valley near daybreak. Overnight lows in the mid 70s.

.SHORT TERM [Wednesday Through Thursday]...

A shortwave trough over the US east coast will move into the western
Atlantic waters on Wednesday with SW flow aloft. At the surface, high
pressure ridging will extend from the western Atlantic into south FL,
keeping west to southwest low level flow over the area with high PWAT
levels well over 2.0 inches remaining over the area. The SW low level
flow will also allow the Gulf coast seabreeze to progress inland and
collide with a weaker Atlantic seabreeze. The shortwave energy aloft,
diurnal heating and seabreeze collisions will lead to numerous showers
and thunderstorm coverage across NE FL and SE GA. Mid level 500 mb
temperatures will be near climatology around -6 to -7 Celsius which
should only support a strong wind gust potential in cell mergers and
locally heavy rainfall due to slow storm motions.

Thursday, the shortwave trough will exit east of the region and mid
level ridging will move in from the NW. Drier air will move in from
the north around surface high pressure centered over the mid south.
Higher PWATS around 2.0 inches will linger over NE FL areas leading
to numerous showers and storm coverage while drier air with PWATs
closer to 1.5 inches should limit storm coverage across SE GA with
isolated to scattered coverage expected.

High temperatures will be in the upper 80s over inland NE FL areas
along the I-75 corridor due to the inward progressing Gulf seabreeze
on Wednesday to around 90 degrees along the first coast and near
seasonal highs in the low 90s on Thursday. Lows Thursday morning
will be in the low to mid 70s inland and the upper 70s at the

.LONG TERM [Friday Through Tuesday]...

A mid level ridge will be NW of the region over the southern plains
while mid to upper level troughing will be over the northeast US.
Surface high pressure will be over the central Gulf of Mexico and
keep light southwest winds over the area. Drier air aloft will limit
convection Friday and Saturday with scattered storm coverage.

The mid to upper level trough will deepen from Sunday into early
next week as a shortwave rounds the base of the east coast trough
and pushes a cold front southward towards the region. This will allow
moisture to increase over the area while shortwave energy aloft and
diurnal heating enhance storm coverage into early next week.

Temperatures will become hotter late this week with mid 90s across
the area Friday into the weekend, then cooling to slightly below
seasonal values early next week in the upper 80s to around 90.
Heat index values will increase to near advisory levels Friday
into the weekend in the 106-110 range.


[Through 06Z Wednesday]

Light southerly winds across NE FL terminals to southeasterly near
SSI, just east of the surface low. Winds will continue back further
WSW this morning across FL terminals and the surface low drifts
farther north, while winds at SSI veer SE to SSW through sunrise
and during the daylight morning hours trailing the low. Most
terminals are low end VFR this early morning, with SSI will be
just below with MVFR cigs through sunrise. After sunrise all
terminals will be VFR. SW winds will bring showers and isolated
tstorms inland from the Gulf Coast region toward GNV through
midday. A weaker east coast sea breeze will back winds at coastal
terminals to SSE in the early afternoon. Giving lingering tropical
moisture, a couple weak surface troughs meandering over the area
and both west and east coast sea breezes, expect an increase in
shower and thunderstorm coverage this afternoon and into the
evening and indicated VCTS for all terminals beginning near 17z
for GNV to 20z for Atlantic coast terminals with TEMPO
thunderstorms between 20z and 24z with reduced VSBYS with the `



Today nearshore waters will have waves of 2 to 3 feet and
offshore waters 3 to 4 feet. The rest of the week the local waters
will have mainly weak winds. Seas 2 feet nearshore, and up to 3
feet offshore. Prevailing winds today will be southerly in the
wake of the low moving up the Georgia coast into South Carolina.
Wednesday through the end of the week, prevailing winds will be
offshore and west-southwesterly. Over the nearshore waters, the
east coast seabreeze will be mainly pinned over the local waters.
A couple afternoons the sea breeze main move near the coast with
winds briefly shifting to the SE/S behind it at 10-15 knots. The
highest coverage of showers/storms will occur late in the day with
the west coast sea breeze will be the most dominate. Cloud-to-
ground lightning strikes and a few wind gusts to 35 knots will be
the main threats to mariners.

Rip Currents: Moderate risk through today. Low risk the rest of
the week.



An area of low pressure north of the Altamaha River Basin will
continue to move northward over the coastal Plains of Georgia
toward South Carolina late in the day. Very weak steering flow
today will allow storms to move very slow this afternoon.
Rainfall rates of 1-3 inches per hour are possible this afternoon
This will lead to locally heavy rainfall, with ponding on roads
and localized flooding possible.

Rivers levels continue to fall with minor flooding ongoing along
the lower portions of the Santa Fe River.



AMG  92  74  89  73  93 /  60  60  80  20  30
SSI  90  77  89  77  91 /  60  50  70  40  30
JAX  92  76  90  75  91 /  60  40  70  40  50
SGJ  91  76  90  75  90 /  50  30  60  40  50
GNV  90  74  89  74  89 /  50  30  80  30  70
OCF  91  74  90  74  90 /  50  30  70  30  70


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