Heavy Rain in Florida, September 19, 2021

Area Forecast Discussion
National Weather Service Jacksonville FL
358 AM EDT Sun Sep 19 2021

...LOCALIZED FLOOD THREAT CONTINUES TODAY-TONIGHT MAINLY OVER
PORTIONS OF NORTHEAST FL...

.NEAR TERM [Through Tonight]...

Current guidance suite continues to show weak west-east low level
troughing from the eastern Gulf coast, through north central FL
and then into the our southern marine waters off of Flagler and St
Johns county. This weak boundary will remain quasi-stationary today
and then begin to lift slowly northward later tonight. Moisture
remains high over most zones with widespread PWATs of 2+ inches
through tonight, and a weak east-northeast low level flow persists
as high pressure ridge remains from GA northeastward to New England.
This setup will favor initial convection again along the coastal
areas through the morning hours, with convection oriented in cells
or northwest-southeast bands due to uniform east- southeast flow
through about 12 kft. With a mid level trough from the central FL
panhandle southeast into northeast FL, slow storm motion and positive
vorticity advection will again support numerous to widespread showers
and storms to mainly inland northeast FL. Areas of heavy rainfall
and localized flooding may develop again and have included heavy
rainfall wording in the grids. Abundant clouds and precip area will
keep highs a bit lower than the past couple of days with highs mainly
in the mid 80s.

Tonight...deep layered moisture and leftover boundaries will
support scattered to numerous showers and storms this evening,
eventually weakening overnight with loss of heating. Focus after
1-2 AM will be more toward the coastal areas again, especially
from St Augustine to Brunswick but with more inland progress over
inland southeast GA. Patchy late night fog will be possible and
lows around 71-75 deg are expected.

.SHORT TERM [Monday Through Tuesday]...

A developing coastal trough may produce bands of heavy rainfall
especially along the se Ga coast where onshore flow and convergence
will increase as strong high pressure builds over the ne U.S.
Heavy rainfall may also occur over inland ne Fl during the
afternoon/evening hours as onshore winds push the east coast
seabreeze well inland. Deep moisture and weak steering winds will
continue the chance for localized flooding.

.LONG TERM [Wednesday Through Saturday]...

An approaching upper trough and cold front to the nw will produce a
sw-w flow over the area on Wednesday maintaining the very moist
and unstable airmass over the area. Showers and thunderstorms will
be likely with the continued threat of heavy rainfall and
localized flooding due to PWATs near 2 inches and a slow storm
motion. The cold front will push se across se Ga Wednesday night
and ne Fl early Thursday morning bringing drier air and lower rain
chances. Surface high pressure will build to the north of the area
which will result in a northeast flow into the weekend. Coastal
convergence and low level moisture behind the front will produce
a chance for mainly coastal showers near the ne Fl coast Thu-
Sat...with dry conditions expected across se Ga. Cooler and less
humid conditions behind the front will result in low temperatures
falling into the low/mid 60s well inland.

&&

.AVIATION...
[Through 06Z Monday]

Through 14Z, generally isolated showers near the terminals with
an isolated cell getting nearly tall enough for a rumble of
thunder near the coast from SGJ to CRG. For now VCSH is included
in TAFs. Fairly good chances of a repeat of low ceilings (IFR or
lower) around GNV and VQQ as well. From around 14Z-00Z, additional
showers and possible isolated thunderstorms will be forming with
the best chances being across the northeast FL coastal terminals.
Highest rain chances in the afternoon hours with numerous showers
and scattered storms. For all TAFs, have included PROB30 and
TEMPO groups for MVFR ceilings/vis but may be lower into IFR.
After 00Z, scattered to numerous showers and storms expected in
the evening but should diminish with loss of heating by 06Z but
anticipate some convection still possible late.

&&

.MARINE...

Variable to light east winds early today will increase to near
10-15 kt by the aftn hours. Seas are a bit lower than NWPS so
slight adjustments were made to the 1st period. Otherwise, winds
tonight will transition to east-southeast tonight and then
southeast on Monday as coastal troughing, oriented more north to
south, develops, and more or less persists into Wednesday. The
abundant moisture, and convergence flow in the low levels will
support daily showers and storms over the area waters. A cold
front moves in late Wed night, with a northerly flow anticipated
by Thursday as the front slides just south of the area waters.

Rip Currents: Moderate risk of rip currents will continue today
through Monday due to onshore flow and easterly swells. Some
longer period swell is noted around 13 seconds today.

&&

.HYDROLOGY...

Minor flooding continues along lower portions of the Santa Fe River
near the Three Rivers Estates gauge. Runoff from numerous to
widespread convection will likely result in river rises across
portions of northeast FL. It is possible additional river flood
warnings may be needed, especially along the Santa Fe River where
heavy rains fell late Saturday.

Locally heavy rainfall and localized flooding will be possible
over the next few days with WPC showing marginal risk of excessive
rainfall. Estimated rainfall amounts into Monday are around 1-2
inches, with locally higher totals possible. Heaviest amounts in
the today- Monday time period look to be over northeast FL and
possibly coastal southeast GA.

&&

.PRELIMINARY POINT TEMPS/POPS...

AMG  85  72  83  71  85 /  70  60  90  40  80
SSI  85  75  84  75  85 /  70  70  90  70  90
JAX  85  74  85  74  87 /  80  60  90  50  90
SGJ  84  74  85  74  86 /  70  60  90  50  90
GNV  85  71  85  71  87 /  80  50  90  30  90
OCF  86  73  87  73  88 /  80  40  90  30  80

&&

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