Area Forecast Discussion
Issued by NWS Jacksonville, FL
FXUS62 KJAX 231907
Area Forecast Discussion
National Weather Service Jacksonville FL
310 PM EDT SAT JUL 23 2016
Afternoon surface analysis depicts high pressure (1021 millibars)
centered near Bermuda, with its axis extending westward across
central FL. Aloft, a massive heat wave ridge is centered over the
Texas panhandle and extends from the desert southwest to the
southeastern U.S. On the far eastern periphery of this ridge, an
upper level cyclone has cutoff just north of the Bahamas.
Northeasterly flow on the western side of this circulation continues
to funnel dry and subsident air into southeast GA, where a meager
and flat cumulus field exists per latest visible satellite imagery.
Isolated convection was developing along the Atlantic sea breeze
over northeast FL as it crosses the St. Johns River. Convection has
been slow to materialize along the Gulf coast sea breeze.
Temperatures at 18Z range from the mid 90s inland to near 90 at the
beaches, compliments of the Atlantic sea breeze. Dry air that was
seen in the low levels on the 12Z Jacksonville sounding is mixing
down to the surface at inland locations, where dewpoints are falling
into the mid/upper 60s, while coastal dewpoints were in the mid 70s
behind the inland moving sea breeze boundary.
.Near Term /through Sunday/...
Convection should gradually increase in coverage along the U.S.
Highway 301 corridor as the afternoon progresses and the Atlantic
sea breeze presses further inland. Hi-res models indicate that the
Gulf and Atlantic sea breezes will meet over central or western
Marion County around 21Z, with outflows from this merger moving
northward and increasing coverage over the Suwannee Valley, during
the late afternoon and early evening hours. The 12Z operational NAM
continues to be the most bullish with coverage over inland northeast
and north central FL, and we increased POPs to likely along the U.S.
Highway 301 corridor in northeast FL from 7 PM-10 PM.
Unseasonably dry air extending into the low levels will enhance the
possibility of microbursts over the Suwannee Valley and the Highway
301 corridor. Outflows from this activity should initiate convection
this evening over our western and southern GA counties, but the
subsident air mass just to the east of these areas should keep
coverage scattered. Otherwise, the upper low just north of the
Bahamas should retrograde slowly westward overnight, perhaps
allowing for high altitude cloud cover to persist over northeast and
north central FL. Debris clouds elsewhere will then after midnight,
with inland lows to fall to the low/mid 70s, with upper 70s expected
at the coast.
The upper level low will continue to retrograde slowly westward
across south FL on Sunday, with some enhanced vorticity pivoting
into northeast and north central FL during the late afternoon hours.
Pockets of higher moisture may also advect onshore, but the overall
environment will remain rather stable for late July, with mid level
temps progged around -6 C. Widely scattered convection should ignite
during the late afternoon hours, with isolated convection possible
into the parched coastal locations as the upper low makes its
closest approach. Rain chances will be higher over north central FL,
closer to the upper low and also where slightly deeper moisture will
be present. Highs will again reach the upper 90s over inland
southeast GA, where heat index values will climb to near 105. Mid
90s are forecast for inland northeast and north central FL, with
lower 90s expected at the coast. Convection will shift westward
towards the I-75 corridor on Sunday evening and should wane by
.Short Term /Monday and Tuesday/...
A weak mid-upper low shifts west of the Fl peninsula into the
eastern Gulf on Monday. Increased moisture will lift north as a se
flow deepens across the area late Monday into Tuesday which should
result in an uptick in rain chances. Scattered coverage of
showers/storms expected for Monday and Tuesday. Temperatures will
remain a few degrees above normal.
.Long Term /Wednesday through Saturday/...
Upper level ridging will remain over the area through the end of the
week. A dry airmass with warm temperatures aloft will keep shower
and thunderstorm activity isolated to scattered. This will lead to
below normal rain chances and above normal temperatures through the
VFR conditions will prevail at the terminals through at least 21Z.
Thunderstorms may approach GNV and VQQ towards 22Z, and activity at
GNV may linger through around 02Z. We included a tempo group for
gusty winds and sub-VFR visibilities at GNV and VCTS at VQQ, where
confidence was lower. Otherwise, southeasterly surface winds of 10-
15 knots will continue through around 23Z at SGJ, SSI, CRG, and JAX.
Variable surface winds at VQQ will become southeasterly near 10
knots around 21Z. Periods of MVFR visibilities are possible at GNV
and VQQ after 06Z through around 12Z, but confidence is currently
too low to include in the TAFs.
High pressure centered near Bermuda will build westward from Sunday
evening through Tuesday across our region, and then will sink
southward and slowly weaken later this week. Onshore winds of 10-15
knots will prevail in the near shore waters through sunset. An
evening wind surge will bring southerly winds up to near caution
speeds, with seas offshore building to 3-4 feet. Winds will then
become southwest after midnight with decreasing speeds during the
predawn hours, with a few thunderstorms possibly developing over the
offshore Georgia waters. A similar weather pattern can be expected
for much of the next week, with a slightly higher chance of
thunderstorms over the FL waters on Tuesday. Winds and seas will
remain below caution levels.
Rip Currents: Low risk continues this weekend.
A hot and dry July continues across much of our region. Here are
some temperature and rainfall statistics through July 22nd at our
designated climate sites:
Jacksonville - Avg Temp 84.2 degrees, 12th hottest since records
began in 1871. Rainfall 1.64 inches, 9th driest thus far.
Gainesville - Avg Temp 83.5 degrees, 7th hottest since records began
in 1890. Rainfall 1.48 inches, 7th driest thus far.
Alma - Avg Temp 84.2 degrees, 2nd hottest since records began in
1948. Rainfall 1.06 inches, 9th driest thus far.
St. Simons Island - Avg Temp 85.3 degrees, 2nd hottest since records
began in 1948. Rainfall 0.45 inches, 2nd driest thus far.
.PRELIMINARY POINT TEMPS/POPS...
AMG 73 97 73 95 / 20 30 20 30
SSI 78 92 77 91 / 10 20 20 10
JAX 73 94 74 93 / 10 30 10 30
SGJ 75 91 75 89 / 10 20 10 10
GNV 72 94 72 92 / 60 50 30 40
OCF 72 95 73 92 / 40 50 40 50