Flood in Florida, September 18, 2022

Area Forecast Discussion
National Weather Service Jacksonville FL
359 PM EDT Sun Sep 18 2022

...PERSISTENT TROUGH THROUGH MONDAY...

...DRYING AND WARMING TREND STARTS TUESDAY...

.NEAR TERM...
(through Tonight)
Issued at 354 PM EDT Sun Sep 18 2022

Water vapor shows the persistent upper level trough lingering
over the FL peninsula while the low level trough axis was inland
across NE FL. A 'kicker' trough was advancing east across
northern GA, and this feature will finally help to begin to drift
the trough axis across the FL peninsula eastward late tonight.

The low level trough axis (or a remnant convergent band) was
oriented W-E in a convective band from southern Duval county
extending offshore of the local coastal waters. NE flow on the
'west' side of the trough axis was steering numerous showers with
embedded t'storms to the SW across inland NE FL, with more
scattered, shallow convection across SE GA triggered by diurnal
heating but under more subsident air on the back side of the upper
level trough. Additional showers were starting to pop along a
hybrid sea breeze/convergent band across St. Johns & Flagler
counties.

Through this evening, diurnally enhanced convection across inland
areas will continue to drift to the SW and then fade quickly
after sunset. A separate batch of convection could develop across
the upper St. Johns River basin through the next few hours, just
east of the trough axis impacting Flagler, Putnam and St. Johns
Counties. The main focus for heavy rainfall potential tonight will
exist along the aforementioned low level trough axis that
extended across Duval County as it slowly pivots northward up the
coast through the night.

Boundary layer winds will remain elevated tonight so expect
mainly low stratus but there could be some shallow ground fog
across inland NE FL where winds will be weaker and rainfall fell
today. Temperatures will trend similar to last nights values from
the upper 60s across inland SE GA to the mid 70s toward the
Atlantic coast and St. Johns River basin.

&&

.SHORT TERM...
(Monday through Tuesday night)
Issued at 354 PM EDT Sun Sep 18 2022

The inverted low level trough lingers over the local Atlantic
waters Monday morning then breaks down and shifts inland with
diurnal heating. Anticipate a similar rainfall pattern as today
with morning coastal convection shifting inland and increasing in
coverage and intensity as it encounters diurnal instability, but,
expect a little less coverage and intensity compared to today as
mid level dynamics will be a bit weaker as the trough axis shifts
a little more east of the local area. The highest rain chances
will focus near the St Johns River basin to the Highway 301
corridor of NE FL in the afternoon. The main convective threat
will continue to be localized heavy rainfall for coastal areas in
the morning, then the heavy precip focus will shift toward the St.
Johns basin westward into the afternoon. Precip will tapper over
inland areas Monday evening, with some coastal overnight into
Tuesday morning mainly for NE FL as ridging begins to settle
southward across GA and shift the trough farther south down the FL
Atlantic coast. Tuesday, drier mid level air reduces rainfall
across SE GA, with the best rain chances near the retreating
trough axis across our southern FL zones.

Temperatures will trend near normal for highs on Monday in the
mid 80s coast to upper 80s inland, then a warming trend ensues
Tuesday ridging begins to strengthen overhead. Highs will warm
into the low 90s Tuesday across SE GA to the mid/upper 80s across
NE FL. Overnight lows will range in the upper 60s well inland to
mid 70s coast, with the cooler lows advecting southward Tuesday
night with the drier air.

Late night fog potential increases over the next few nights.
Better inland fog potential occurs Monday night where patchy fog
was indicated for SE GA and the Suwannee River Valley.

&&

.LONG TERM...
(Wednesday through Sunday)
Issued at 354 PM EDT Sun Sep 18 2022

Wed & Thu: HOT and mostly dry as a strong mid level ridge
centered across TX extends a ridge axis east across across the
Gulf Coast states. Near the surface, a weak coastal trough will
bring a low chance of showers across our southern FL zones Wed
while the remainder of the area remains dry as a surface ridge
builds overhead. Dry and even hotter conditions will continue into
Thu as the surface ridge builds over the local area. The main
weather impacts this period will be the hot temps warming well
above climo from the mid/upper 90s across inland areas to the
upper 80s at the coast as well as dangerous as well as frequent
rip currents and rough surf increasing at local beaches due to
long period easterly swells from distant TC Fiona as the cyclone
tracks northward well east of the local waters.

Fri through Sun: Continued mostly dry conditions with a cool down
to seasonably warm temperatures trailing the passage of a dry
"cool" front Friday. The upper ridge builds over the local area
next weekend with low level onshore flow and weak coastal troughs
forming once again over the local Atlantic waters. This pattern
will bring breezy conditions to coastal areas and a low chance of
coastal showers across our southern FL forecast zones into the
weekend. The main weather impact this period will continue to be
focused at the coast where frequent rip currents are expected with
rough surf.

&&

.AVIATION...
(18Z TAFS)
Issued at 200 PM EDT Sun Sep 18 2022

MVFR and some brief IFR conditions will affect the regional
terminals to begin the 18Z TAF period as heavy showers and moist
onshore flow continues this afternoon. A few embedded storms with
gusty, variable winds up to 25 knots are also possible and
have the TAF sites covered with TEMPO groups for low MVFR to IFR
ceilings and visibilities largely caused by heavy rain rates.
Have KSGJ covered with LIFR ceilings through 20Z due to locally
heavy rain driven lower ceilings over the site. Wave of showers
and storms will move south and west around the weak low located
over the duval county terminals with breezy northeast winds 12-15
knots gusting to 20-25 knots at the coastal TAF sites with 8-12
knots at the inland sites. Gusty winds up to 25 knots possible in
heavier bands of showers and storms. Winds will decrease inland
to around 5-8 knots and stay elevated at the coast around 10 knots
with by evening/00Z and scattered showers will occasionally come
ashore at the TAF sites along and east of I-95 overnight prompting
VCSH overnight with low status/IFR ceilings developing at the
inland TAF sites after 06Z with LIFR ceilings possible at KGNV and
have a TEMPO Group at KGNV to note this potential. Scattered to
numerous showers will begin to develop after 14Z over the
terminals on Monday keeping at least VCSH coverage with winds
increasing again to 10-12 knots at the coastal sites and 5-8 knots
at the inland sites from the northeast with VFR ceilings
scattered around 2.5 kft to end the period.

&&

.MARINE...
Issued at 354 PM EDT Sun Sep 18 2022

A persistent coastal trough will continue onshore flow with
numerous showers and isolated thunderstorms through Monday. The
trough will weaken and shift southward Tuesday as high pressure
begins to build across the Georgia waters from the north. High
pressure will extend over the local waters Wednesday into Thursday
with much drier conditions as long period swells from distant
Tropical Cyclone Fiona increase. Small Craft Advisory headlines
are possible due to combined seas Wednesday through late Thursday.
A dry front will press south across the local waters Friday
trailed by northerly winds.

Rip Currents: High risk today for SE GA beaches, moderate for NE
FL beaches. An elevated (high to moderate) rip current risk is
expected Monday & Tuesday with onshore flow, then the rip current
risk is expected to return to High Risk for all local beaches by
Wednesday through Friday as long period (14-15 second) easterly
swells from distant TC Fiona enter the local waters.

&&

.HYDROLOGY...
Issued at 354 PM EDT Sun Sep 18 2022

Elevated tidal levels are expected at the coast and within the St.
Johns River basin this upcoming week due to the combination of
onshore flow; annual elevated astronomical tidal levels; the
approach of the New Moon on 9/25; and, for the St. Johns basin,
fresh water drainage from the upper portions of the basin. Expect
tidal departures to remain below Minor flooding levels based on
the latest PETSS guidance, below Coastal Flood Advisory criteria.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  69  88  69  92 /  10  30  10  10
SSI  74  84  75  86 /  40  60  20  20
JAX  72  85  72  87 /  40  60  30  30
SGJ  73  83  73  85 /  50  60  40  50
GNV  71  86  70  88 /  30  70  40  40
OCF  71  87  72  88 /  30  70  40  50

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...High Rip Current Risk until 10 PM EDT this evening for GAZ154-
     166.

&&