Area Forecast Discussion
Issued by NWS Jacksonville, FL

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FXUS62 KJAX 281138

Area Forecast Discussion
National Weather Service Jacksonville FL
738 AM EDT Wed Jul 28 2021

[Through 12Z Thursday]

Light westerly winds today will go calm again overnight. Scattered
showers have already popped up this morning near GNV and SSI.
Further development of showers and storms expected along the Gulf
sea breeze in the late morning/early afternoon. Storms should push
inland, mainly affecting the Florida TAF sites in the afternoon
and evening. Storms across Florida will linger through mid to late
evening, and dissipate around 03Z. Some of the stronger storms
this afternoon and evening may have gusts to 40 mph with rounds
of localized heavy rains briefly providing MVFR to possible brief
IFR conditions.



.NEAR TERM [Through Tonight]...

Through daybreak...Stratiform rain has lifted north of the
Altamaha River Basin. One lone shower and thunderstorm is
over of the southern Big Bend region of Florida. Some additional
convective development over the northeast Gulf of Mexico and the
west coast of Florida before dawn within the very moist southwest
flow. Some convection may spill further inland around dawn or
shortly there after into the Suwannee Valley.

Today and Tonight...
The main focus of convection today will be along the trough axis
in the wake of 90L that currently extends from Southeast Georgia
into the FL Panhandle. This trough will slowly drift to the south
and east as the day progresses and will be the primary focus for
scattered to numerous showers and thunderstorms this afternoon and
evening. The combo of the this trough and also a mid level short
wave diving south and east, and precipitable water values between
2 and 2.3 inches. Expect convection to initially be triggered by
the inland moving Gulf coast sea breeze by the late morning hours
in western portions of the Suwannee Valley. Mesoscale boundary
collisions will then increase coverage and intensity of convection
by late afternoon as activity generally moves slowly eastward,
with a few storms possibly pulsing towards late afternoon as
convection encounters the pinned Atlantic sea breeze boundary at
coastal locations. Localized flooding will be possible due to slow
storm motion, particularly at urban and normally flood prone
locations. Similar to the last couple days, some storms are
capable of producing rain rates of 1.5 to 3 inches per hour in
isolated pockets. Some of the stronger storms will produce
frequent lightning strikes and briefly gusty downburst winds up to
40 mph. Highs will climb to the upper 80s to near 90 before
convection and cloud cover increase during the early to mid
afternoon hours, with maximum heat index values of 100 to 105. By
mid evening convection will slowly diminish over SE GA as the
surface trough and mid level short wave shifts more over NE FL,
with convection probably not waning over NE FL until late evening.
Debris cloudiness will linger over the region overnight, while
convection commences over the NE GOM shifting inland toward the
Suwannee Valley around sunrise. Temperatures tonight will get
generally be in the mid 70s.

.SHORT TERM [Thursday Through Friday]...

A warming and drying trend north to south as an anomalously strong
dome of mid level high pressure centered across the central CONUS
extends a ridge axis eastward across southern GA, shifting the
sheared out mid/upper level trough axis and deeper moisture
southward across the FL peninsula. Precipitable water (PWAT) falls
below climo values across SE GA as drier mid level air intrudes
from the NNE which will limit precipitation potential both days.
At the surface, a surface trough will edge SSW across NE FL Thu,
which will serve as a convective focus into the afternoon as this
boundary interacts with the sea breezes and outflows across inland
NE FL where near climo PWATs will continue. By Fri, PWAT lowers
below normal for zones north of the I-10 corridor with the best
diurnally enhanced rain chances from GNV to SGJ southward, but
with a little less coverage compared to Thu with drier mid level
air in place. The main weather hazards from isolated strong storms
will be locally heavy rainfall across NE FL Thu given weak storm
motion and gusty wet downbursts will be possible with elevated
DCAPE given drier air in place both days.

The main weather story during this time period will be the
increasing heat with dry bulb temps above normal in the mid to
upper 90s and these values combined with surface dew pts in the
mid/upper 70s heat index values will range from 105-110 degF.
Local Heat Advisory criteria is for heat index values 108-112
degF. At this time, appears Heat Advisory potential will exist for
parts of SE GA by Friday.

.LONG TERM [Saturday Through Wednesday]...

Models are in good agreement with the synoptic pattern this
weekend into early next week with a surface front meandering
across central GA and the Bermuda ridge axis across south FL.
Aloft, the strong mid level ridge axis will shift southward across
NE FL into Sat, continuing hot temps and elevated heat index
values near heat advisory criteria. PWAT begins to increase late
Sat into Sun as the upper ridge breaks down and zonal flow
develops aloft, with weak WSW steering flow developing across the
local area. Rain chances increase late Sun into Tue with both
GFS/ECMWF indicating a long wave trough deepening across the
eastern CONUS with a return of PWAT above 2 inches and waves of
PVA aloft enhancing diurnally enhanced storms under stronger WSW
steering flow over the local area. Overall, the developing pattern
into the weekend favors a dominant west coast sea breeze which
will shift inland through the afternoon, with the highest rain
chances focused east of Highway 301 toward the Atlantic coast in
the afternoon and evenings where sea breezes and outflows collide.
Temperatures will continue above normal early this weekend, then
trend below climo into early next week due to increased convection
and cloud cover.


A weak trough of low pressure positioned near the FL/GA border
will shift southward over the northeast FL waters by Wednesday
night and will then dissipate by Thursday night. Numerous
thunderstorms developing over land on Wednesday afternoon will
move across our local waters during the late afternoon and evening
hours, with stronger activity containing frequent lightning
strikes and briefly gusty winds. Seas of 2-3 feet will prevail
today and Thursday for both near shore and offshore. Thunderstorm
coverage will then decrease over the Georgia waters by Thursday
afternoon and then for all local waters on Friday. Seas will
decrease to the 2-4 foot range from Thursday through the weekend.
A weak cold front will then dive into the southeastern states
during the weekend, resulting in gradually strengthening
southwesterly winds and increasing chances for afternoon and
evening thunderstorms as the weekend progresses, with widespread
thunderstorm activity expected early next week as the frontal
boundary stalls over the GA waters.

Rip Currents: Prevailing offshore winds should result in a low
risk at most area beaches through midweek.


Elevated rain chances continue today as tropical moisture lingers
over the region. A warming and drying trend begins Thursday
across southeast Georgia and expands across northeast Florida into
Friday as temperatures rise into the mid to upper 90s with
dangerously high heat index values near 105-110 degF. The highest
rain chances will focus south of I-10 across NE FL both
afternoons. Low daytime dispersions are expected today for the
southeast Georgia coast extending inland across the Okefenokee NWR
and Osceola NF near a weak low level trough axis where transport
winds will be weak. Thursday this trough axis will slide southward
across northeast Florida and create low daytime dispersion.


Minor river flooding continues for the Santa Fe basin.



AMG  90  74  94  74  97 /  50  30  20   0  10
SSI  90  77  91  78  94 /  40  40  30   0   0
JAX  91  74  91  75  97 /  70  70  40  10  10
SGJ  90  74  89  75  94 /  70  70  40  10  10
GNV  89  74  90  74  94 /  60  60  60  40  30
OCF  90  74  90  75  93 /  60  40  60  30  40


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