Heavy Rain in Florida, August 25, 2022

Area Forecast Discussion
National Weather Service Jacksonville FL
1245 PM EDT Thu Aug 25 2022

...SLOW MOVING THUNDERSTORMS EXPECTED EACH AFTERNOON AND
EVENING THROUGH SATURDAY...
...LOCALIZED FLOODING POSSIBLE, ESPECIALLY AT URBAN AND INLAND
LOCATIONS..

.UPDATE...
Issued at 1245 PM EDT Thu Aug 25 2022

Early afternoon surface analysis depicts a stalled frontal boundary
situated along the FL/GA border, with weak low pressure (1012
millibars) located further westward along this stationary front
over coastal Louisiana. Meanwhile, high pressure (1020 millibars)
was located in the wake of the front over the Carolinas.
Aloft...ridging remains in place over the Bahamas and south FL,
with a broad trough extending across the lower Mississippi Valley
and the Deep South. This weather pattern was keeping deep
southwesterly flow above 700 millibars (around 10,500 feet)
locally per the morning sounding at Jacksonville, with embedded
shortwave troughs exiting the Georgia coast and also located
upstream of our region near the western FL panhandle. Latest
RAP/LAPs analyses confirm the presence of deep tropical moisture
throughout our region, with PWATS around or above 2 inches. Widely
scattered convection was already developing along the coast, as
the Atlantic sea breeze boundary was beginning to push inland.
Otherwise, a few sprinkles were progressing across inland portions
of southeast GA, mainly to the north of Waycross, where a thicker
cirrostratus shield was in place. A healthy cumulus field was
developing elsewhere. Temperatures beneath the thick cirrostratus
were only in the lower 80s for locations north of Waycross, with
breezy onshore winds just north of the stalled front also keeping
coastal southeast GA in the lower 80s. Temperatures were
otherwise climbing through the mid and upper 80s, with dewpoints
in the 70s area-wide.

Convection has initiated earlier than it did yesterday along the
Atlantic sea breeze boundary, and these showers and thunderstorms
should continue to increase in coverage as they interact with
other mesoscale outflows and boundaries such as the St. Johns
River breeze. Widespread coverage is forecast between the
Interstate 75 and U.S. Highway 301 corridors by late afternoon and
early evening as the Gulf coast sea breeze becomes involved in the
equation, and convection should also overspread inland southeast
GA as the upstream shortwave approaches, with the stationary
frontal boundary also fostering development later this afternoon.
Weak southwesterly steering flow will again result in slow storm
motion, with localized flooding increasingly becoming a concern,
as inland locations in northeast and north central FL are now
saturated after prior days of heavy rainfall totals. Urban areas
along the I-75 corridor such as Ocala, Gainesville, Lake City and
Live Oak will be most prone to localized flooding later this
afternoon and into the evening hours. A few storms will also
likely pulse and become strong as mesoscale boundaries collide,
with stronger convection possibly producing localized wind gusts
of 40-50 mph, along with frequent lightning strikes. Highs will
generally climb to the upper 80s to around 90 before convective
coverage and cloud cover increase, except mid 80s for locations
north of Waycross and along the southeast GA coast.

Convection should push slowly northeastward back across the
U.S.-301 corridor early this evening, possibly reaching the I-95
corridor before weakening later this evening. Debris cloud cover
will be slow to thin out overnight, with light showers and
sprinkles remaining possible to the north of the front across
southeast GA through the early morning hours. Lows will generally
fall to the low and mid 70s, with a few upper 70s possible at
coastal locations.

A similar weather pattern will prevail on Friday as the stalled
boundary and trough remain over our region. Flow aloft will veer
slightly to west-southwesterly, which may give a little more push
to the Gulf coast sea breeze during the afternoon hours, possibly
spreading a higher coverage of convection towards the I-95
corridor by the late afternoon and evening hours. Heavy downpours
and localized flooding will remain the primary threat from the
widespread convective coverage that is forecast. Highs will
generally reach the 85-90 degree range before convective coverage
and cloud cover increases during the afternoon hours.

&&

.MARINE...
Issued at 1245 PM EDT Thu Aug 25 2022

A weak frontal boundary will remain stationary near the border of
Florida and Georgia through Friday night before dissipating over
the weekend. Meanwhile, the axis of Atlantic high pressure will
remain situated across the Florida peninsula through Saturday,
with a loose pressure pattern prevailing over our local waters
through the weekend. Showers and thunderstorms will develop along
the coast during the late morning and early afternoon hours as the
sea breeze develops and pushes inland, with evening and overnight
activity possible through the weekend as thunderstorms track back
towards the coastal waters after sunset. Atlantic high pressure
will then build westward towards the southeastern states late this
weekend and early next week, resulting in a prevailing onshore
flow pattern, which should shift the timing of showers and
thunderstorms to the overnight and early morning hours across our
local waters. Seas of 2 to 3 feet will prevail both near shore and
offshore through the upcoming weekend.

&&

.FIRE WEATHER...
Issued at 1245 PM EDT Thu Aug 25 2022

Light northwesterly surface and transport winds will shift to
easterly this afternoon, resulting in marginally low daytime
dispersion values at most locations. Showers and thunderstorms
will increase in coverage and intensity along the inland moving
Gulf and Atlantic coast sea breezes this afternoon, with
widespread coverage anticipated for locations along the Interstate
75 corridor during the late afternoon hours, with activity then
progressing slowly northeastward towards the U.S. Highway 301 and
I-95 corridor by the early to mid evening hours tonight. Slow
moving thunderstorms will be capable of producing heavy downpours,
with a few stronger storms creating frequent lightning strikes
and briefly gusty winds. Surface and transport winds will shift to
westerly and will remain light outside of thunderstorm activity
on Friday, resulting in another day of marginally low daytime
dispersion values at most locations. Widespread mainly afternoon
and evening showers and thunderstorms are expected from Friday
through the upcoming weekend.

&&

.HYDROLOGY...
Issued at 1245 PM EDT Thu Aug 25 2022

Additional 1-3 inch rainfall totals are expected through Friday
on widespread basis for inland locations, with locally higher
totals possible. Amounts at coastal locations will likely be in
the 0.5 - 1.0 inch range. The Weather Prediction Center has
included our entire area within a marginal risk for excessive
rainfall amounts through Saturday, with localized flooding
remaining a distinct hazard, especially if downpours train or
backbuild over urban or normally flood prone locations.

&&

.AVIATION...
[18z TAFS]
Issued at 1240 PM EDT Thu Aug 25 2022

Latest observations and satellite imagery showing areas of MVFR
cigs around TAF sites. Radar is showing early start to sea breeze
convection along east coast. This activity will spread/redevelop
westward...affecting coastal TAF sites through 20-21z, JAX area
sites 19z thru 23z...and KGNV 20z through 00z or shortly after
that. Going with TEMPO for that period in 18z TAFs.  Could see
strong gusty winds in more intense cells that develop. Activity
decreases during the evening. Latest guidance suggests return of
IFR cigs late at night, perhaps after 08z, with cigs increasing to
MVFR range by late morning Friday.

&&

.NEAR TERM...
Issued at 319 AM EDT Thu Aug 25 2022

Some showers and isolated storms remain along portions of the
coast near Mayport into the waters as shortwave energy traverses
our area just ahead of a cold frontal boundary sinking slowly
across SE GA. Otherwise winds are near calm inland and from the
south to southeast along the coast around 5 mph as mostly cloudy
skies linger overnight. Dewpoints are a tad higher compared to
this time yesterday morning in the mid 70s as the front nears and
yesterday's locally heavy rains keep surface moisture abundant
with temperatures holding generally in the mid 70s to near 80
degrees at the coast.

Another day of wet and stormy conditions will develop later today
as diurnal heating, abundant moisture, and incoming shortwave
energy aloft help spur isolated to scattered showers and storms
by late this morning. Then, with the Atlantic seabreeze moving
well inland ahead of the front, seabreeze collisions between
Highway 301 and I-75 will yield numerous to widespread showers
and scattered thunderstorms. The high moisture content, as in
previous days, will allow for very heavy rainfall rates with
storms and heavier showers moving very slowly back to the NE as
the SW flow above the boundary layer overrides low level onshore
easterly flow behind the Atlantic seabreeze. Some wet downburst
winds generally under 50 mph are also possible with the heaviest
storms as will be locally heavy rainfall amounts of 1-3 inches.
General rainfall amounts will total close to an inch or so for
most of the area. Local flooding concern potential continues
most notably for urban areas with poor runoff. Highs today will
reach into the mid to upper 80s over SE GA and along the coast
with upper 80s to around 90 over NE FL and low 90s over north
central FL. Light northerly winds will become easterly 5-10 mph
under mostly cloudy skies with heat index values approaching 105
across NE FL.

Tonight, some isolated to scattered showers will drift east off
the coast after midnight with cloudy skies lingering as low
cloud cover blankets areas along and north of I-10 where the
front will begin to stall. Some patchy fog form over NE FL areas
that receive locally heavy rainfall, but cloud cover should limit
coverage tonight. Lows will fall into the lower to mid 70s inland
and the mid to upper 70s at the coast.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  85  71  89  72 /  60  40  60  30
SSI  87  75  87  76 /  60  50  60  40
JAX  89  73  90  73 /  70  60  70  40
SGJ  89  75  89  74 /  60  60  70  30
GNV  91  71  90  72 /  80  70  70  30
OCF  91  72  90  72 /  70  60  70  30

&&

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