Flood in Florida, December 5, 2018

Area Forecast Discussion
National Weather Service Jacksonville FL
304 PM EST Wed Dec 5 2018

...LIGHT FREEZE WITH AREAS OF FROST INLAND SE GA/NE FL TONIGHT...

...WIDESPREAD RAINFALL AND ISOLATED STORMS EXPECTED THIS WEEKEND...

.NEAR TERM /Tonight-Thursday/...

Tonight...Cold High Pressure builds into the SE US tonight with
light freeze still expected over inland SE GA and portions of
inland North Florida generally west of the US301 corridor. Mainly
clear skies are expected with just a few passing thin cirrus
clouds at times. Not likely enough to impact the overall low temp
forecast. Lows in the upper 20s to near 30 degrees across inland
areas under the current Freeze Warning. Lows generally in the
lower to middle 30s along the I-95 corridor and upper 30s to near
40 along the Atlc Coast as winds become onshore by morning. Areas
of Frost expected in the Freeze Warning area, with some patchy
frost expected down the I-95 corridor and St Johns River Basin
counties of NE FL.

Thursday...Sfc High Pressure remains over the SE US and nudges
slightly towards the Carolinas and surface flow becomes light NE
and expect a combination of some thin cirrus aloft and some Cu
development near the coast, but overall Mostly Sunny conditions
with slightly cooler than normal Max Temps in the 50s across SE GA
and lower 60s across NE FL.

.SHORT TERM /Thu Night-Fri Night/...

Thu Night...Sfc High pressure remains just north of the region
with light N-NE sfc flow continuing and still some cirrus clouds
aloft and Strato-Cu along the coast but overall still Mostly Clear
to Partly Cloudy skies with cool temps once again ranging from the
30s inland to 40s along the coast. Not expecting another Freeze
but some patchy frost still possible once again over inland SE GA
and inland North FL/Suwannee River Valley.

Friday...Clouds begin to increase from the West in the zonal flow
aloft with more substantial Cirrus shield by the afternoon, with
just partly sunny filtered sunshine and cool NE flow slowly
increasing at the surface especially along the coast to 10-15 mph.
Temps slightly closer to climo values with highs in the lower 60s
SE GA and mid/upper 60s NE FL.

Fri Night...High pressure remains just north of the region with NE
surface flow but steering flow becomes Southerly below 10KFT and
expect milder overnight lows in the 40s inland/50s coast and
mid/upper level cloud cover continues to increase and thicken with
Mostly Cloudy skies developing.

.LONG TERM /Saturday-Wednesday/...

Sat/Sun...Models still trying to refine the details but overall a
strong southerly jet, very much in line with the developing El
Nino conditions in the Pacific will develop a strong low pressure
over the Northern GOMEX on Saturday with expected track eastward
along the FL Panhandle Sat Night and crossing somewhere across NE
FL/SE GA while intensifying on Sunday. Overall impact of this
development will be skies becoming cloudy on Saturday with
onshore E-NE flow increasing and rain chances increasing as well
with scattered showers by the afternoon hours. Strong southerly
low level jet ahead of low of at least 50 knots will help produce
widespread rainfall Sat Night into Sunday Morning with embedded
storms expected area-wide due to strong dynamics with this system.
Any Surface based strong to severe storms will depend on the
exact track of the low pressure which at this point should be
along the FL/GA border late Sat Night/early Sunday and will likely
limit surface instability to NE FL south of the I-10 corridor
with best chances of severe storms south of a line from GNV-SGJ.
Temps push back to slightly above normal levels with Highs in the
50s/60s SE GA and into the lower/middle 70s for NE FL mainly south
of I-10. This will be similar to normal winter-time thunderstorm
events with lack of instability the main question across NE FL as
dewpoints expected to rebound into the mid/upper 60s, a far cry
from the lower to middle 70s dewpoints in the last severe weather
event last weekend. Low rapidly pushes offshore by Sunday Night
with dry slot punch aloft and expect moderate to heavy rainfall on
Sat Night/Sunday to end and become low end showers and drizzle
for Sunday Night with dreary/cold conditions as temps fall into
the 40s area-wide. Rainfall Totals for this event will be lower
than last weekend due to the progressive nature of the low
pressure system with widespread 1-2 inch amounts and locally
higher amounts 3-4 inches possible across SE GA just to the North
of the eventual low track which could still cause significant
flooding issues based on the saturated ground conditions and a
Flood Watch may be needed for the Sat Night/Sunday time frame.

Monday...Cold and raw conditions will continue in the NW
wraparound conditions from departing low pressure and while some
sunny breaks are possible by the afternoon, expect highs only in
the 50s for most locations and maybe not breaking 50 for inland SE
GA if the cloud cover holds in all day. Measurable Rain chances
relatively low at 20 percent or less with most likely drizzle and
low clouds continuing through the morning hours.

Tue/Wed...High pressure builds north of the region and flow
becomes North on Tue and Northeast on Wed with generally Mostly
Clear to Partly Cloudy skies and seasonably cool conditions. Highs
still only in the 50s on Tuesday and 60s on Wednesday with lows in
the 30s inland and 40s along the coast. Sub-freezing temps at
night are not expected at this time due to the high pressure too
far north of the region and pressure gradient not relaxing and
keeping at least light winds around 5 mph during the overnight
hours.

&&

.AVIATION...
VFR conditions will prevail through the period with few/sct
cirrus. Northwest winds around 10 knots with gusts to around 20
knots this afternoon will become light 5 knots or less tonight.
High pressure will build to the north of the region tonight and
Thursday, and a light north to northeast flow will prevail.

&&

.MARINE...
Strong NW flow assocd with SCA flags offshore and SCEC headlines
nearshore waters will slowly weaken as high pressure builds closer
to the region with winds becoming North on Thu and Northeast on
Friday at 10-15 knots and seas falling to 2-4 ft. High pressure
wedging down the SE US coast on Saturday will increase onshore
E-NE winds to 20-25 knots ahead of next system with building seas
and expect Small Craft Advisory conditions again and these will
continue into early next week as low pressure system tracks across
or just north of waters on Sunday and strong offshore winds
develop in the wake of the low Sunday Night into Monday and some
Gale Force Wind gusts not out of the question along with seas
building to 6 to 9 feet offshore.

Rip Currents: Low Risk in the offshore flow.

&&

.FIRE WEATHER...
Min Humidity levels the next couple of days should remain above
critical levels while weak transport winds will support low
daytime dispersions the next couple of afternoons over inland SE
GA.

&&

.HYDROLOGY...
Minor Flooding will continue along the Atlamaha and Satilla River
Basin, while the Alapaha River is cresting at Moderate Levels
today and Thursday. Minor flood wave pushing down the Middle
Suwannee River basin this weekend will allow for a Backwater Minor
Flood Event to develop on the lower Santa Fe River Basin.

&&

.CLIMATE...
Forecast strength of the low pressure system to be around 1005mb
to 1007mb as it passes through the region on Sunday December 9th
and this will be close to record low SLP for this date at local
climate sites which are listed below...

JAX 1004.7 mb 12-09-1903
GNV 1006.6 mb 12-09-1989
SSI 1006.3 mb 12-09-2009

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  28  55  33  60 /   0   0   0   0
SSI  37  56  42  60 /   0   0   0   0
JAX  33  60  39  63 /   0   0   0   0
SGJ  39  61  46  65 /   0   0   0   0
GNV  32  61  38  67 /   0   0   0   0
OCF  33  63  40  70 /   0   0   0   0

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...Freeze Warning from 3 AM to 8 AM EST Thursday for Alachua-Baker-
     Bradford-Columbia-Gilchrist-Hamilton-Inland Nassau-Suwannee-
     Union.

GA...Freeze Warning from 3 AM to 8 AM EST Thursday for Appling-
     Atkinson-Bacon-Brantley-Charlton-Clinch-Coffee-Echols-
     Inland Camden-Inland Glynn-Jeff Davis-Pierce-Ware-Wayne.

AM...Small Craft Advisory until 4 AM EST Thursday for Waters from
     Altamaha Sound GA to Fernandina Beach FL from 20 to 60 NM-
     Waters from Fernandina Beach to St. Augustine FL from 20 to
     60 NM-Waters from St. Augustine to Flagler Beach FL from 20
     to 60 NM.

&&

Hess/Kennedy/McGinnis