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Area forecast discussion
National Weather Service Jacksonville Florida
914 am EST Tue Nov 12 2019

..strong cold front to blast through area today...

Update...

A very strong cold front was moving through central Georgia this
morning. Light to moderate showers were along and ahead of the
cold front, and will reach the northwestern portion of the area in
the next couple hours. High rain chances are forecast across
southeast Georgia and from a Gainesville to St. Augustine line
northward. Overall rainfall amounts will be a few hundredths to a
quarter of an inch. Patchy dense fog and low stratus was beginning
to lift this morning, and increasing southwesterly winds will
allow temperatures to warm to above average across much of the
area.

The cold front will blast through the region this afternoon
into the early evening, with breezy winds quickly shifting to the
northwest behind the front. High temperatures today will be near
70 across northwestern portions of southeast Georgia to the upper
70s to lower 80s across northeast Florida. The front is forecast
to be near Jesup to a Live Oak line around 18z, and then push to
near Flagler Beach to the southeastern corner of Marion County by
00z. Temperatures will fall quickly behind the front, falling just
after noon across interior southeast Georgia. Temperatures will
fall into the upper 40s to lower 50s across interior southeast
Georgia and the Suwannee Valley by 7 PM this evening, the upper
50s to lower 60s north of a line from Gainesville to Ponte Vedra,
and mid 60s to lower 70s southward.

It will be cold tonight, especially across southeast Georgia where
temperatures could fall to near 30 degrees and wind chills near
20. For northeast Florida, there will be a sharp gradient, with
lows in the mid 30s for the Suwannee Valley and near the Florida/Georgia
border to the low to mid 50s towards Flagler County due to the
onshore winds developing. A freeze watch is in effect for much of
southeast Georgia, and this will likely need to be upgraded to a
freeze warning later today. Winds will shift to the north
northeast overnight, with gales over the marine waters. Windy
conditions are expected at the beaches, and a Wind Advisory may
be required for coastal northeast Florida overnight. In addition,
rough surf and beach erosion is expected, and a high surf advisory
will also likely be needed for the northeast Florida coast. Water
will backup in the St. Johns River tonight and through Wednesday
with the strong north northeast winds. The strong onshore flow and
full moon will likely lead to coastal flooding along the coast and
in the St. Johns River, and a coastal Flood Warning will likely be
needed for Wednesday for northeast Florida and the St. Johns River
with a coastal flood advisory northward.



&&

Aviation...
[through 12z wednesday]
some patchy IFR/MVFR vsbys in fog at vqq/gnv early this morning
otherwise VFR conds ahead of the approaching cold front with
frontal passage and shower activity expected in the 19-21z time
frame at the taf sites with a sharp wind shift to northwest at 10-12
knots and lowering of ceilings to MVFR in the 1500-2500 ft range.
Showers fade after a few hours but low MVFR ceilings remain through
the 03-06z time frame as north winds increase to 14-16 knots, some
clearing possible at the inland taf sites of gnv/vqq and northern
taf sites of ssi depending on the back edge of the cloud shield
by 09-12z.

&&

Previous discussion [329 am est]...

Near term [through tonight]...

Today...some patchy early morning fog, otherwise warm conditions
ahead of the strong cold front today with highs ranging from the
70s across southeast Georgia to around 80 degrees across NE Florida. Hi-res models
in good agreement with the timing of the front entering southeast Georgia late
this morning in the 10am-11am time frame and make a quick 6-8 hr
trek from northwest to southeast across all of southeast Georgia and exiting to the southeast into
the Atlc and cntrl Florida by the 4pm-6pm time frame. This will lead to
many areas reporting their Max temps early in the day with falling
temps across most of southeast Georgia and parts of the I-10 corridor during
the afternoon hours. While rainfall amounts will generally only be
a tenth of an inch or so, rainfall chances will be fairly high
during the small period of cold frontal passage and for a few
hours following the front.

Tonight...strong cold air advection behind the front from the
north will usher in the coldest airmass of the season with an
advective light freeze possible across southeast Georgia and have posted a
freeze watch for possible brief light sub-freezing temps in the
5am to 9am time frame Wed morning with lows close to 30 degrees
and wind chills falling into the 20s by morning as well. Other
than the significant cold airmass arrival the north winds will
likely increase to 20 to 30 mph along the coast with gusts to 40
mph possible at the immediate beaches and a Wind Advisory may need
to be posted with the next forecast package. Lows will generally
be in the mid to upper 30s from coastal southeast Georgia through the west jax
Metro area and along the I-10 corridor but likely too much wind to
expect much frost formation except for some sheltered locations
across inland southeast Georgia in the freeze watch area where skies also have
the best chance of clearing towards morning. Lows in the 40s
generally expected from the east jax Metro area down the St Johns
River basin and into the gnv/ocf area. Any rainfall behind the
front in the evening hours should end by midnight and clearing
skies inland are expected with some lingering clouds along the
coast. Morning lows Wednesday will likely not reach record levels
but will Post here for reference purposes...

Jax 31/1987...gnv 29/1906...amg 28/1963...ssi 33/1968...crg 32/1987



Short term [wednesday through saturday]...

High pressure will build to north Wednesday, then northeast
Wednesday night into Thursday. Onshore flow will result from this
pattern. An inverted coastal trough is expected to develop in this
flow. The combination of the strong high pressure ridge and the
trough will result in an enhanced pressure gradient over the
region. This will produce a elevated winds through Thursday,
especially near the coast. As a result, coastal flooding chances
will increase this period. The chance for mainly coastal showers
will increase Wednesday into Thursday.

An inverted trough will develop over the eastern Gulf Thursday,
which will move east across the forecast area Thursday night into
Friday. Rain chances will increase over area as a result. Once this
trough gets east of the region, it may develop into a low, which
will move to the east northeast on Saturday. So the onshore pattern
may weaken a bit Thursday night into Friday, but will strengthen
Friday night into Saturday. This could result in another prolonged
period of coastal flooding potential, in addition to gusty winds.

Wednesday will be the coolest day this period, with highs about
10 to 15 degrees below seasonal averages, but readings are expected
to be below normal through the period, especially during the day
time.



Long term [saturday night through tuesday]...

High pressure will build from the west northwest over the weekend
into early next week. Away from the coast, a dry period is expected.
Temperatures to remain below normal into Monday, then return to near
normal by Tuesday.



Aviation...
[through 06z wednesday]

Brief MVFR ceilings at sgj overnight, otherwise VFR with some IFR
visibilities developing towards morning at gnv/vqq in fog along with some
MVFR visibilities at jax/crg as well. Main event for the taf set on
Tuesday will be the arrival of strong cold frontal passage from northwest
to southeast impacting the taf sites in the 20-22z time frame with
increasing northwest winds to 10-15 knots and widespread MVFR ceilings of
1000-2000 ft along with MVFR visibilities in showers as well. These will
last approx 3-5 hours then rainfall ends at inland taf sites as
winds shift to the north and increase to 15 knots with gusts of
20-25 knots with continued MVFR cigs, except for a continued
trend downwards to IFR ceilings and continued rainfall at sgj along
the NE FL coast.



Marine...
forecast still on track with offshore flow today at 10-20 knots
ahead of the cold front with a sharp increase to north winds at 25
to 30 knots with frequent gusts to 35-40 knots tonight in the
strong cold air advection and have upgraded to a Gale Warning for
all of the coastal waters which will last into Wednesday with seas
building up to 7-13 ft. Winds generally remain northeast to north
the rest of the week with strong high pressure north of the waters
and Small Craft Advisory conditions will last well into next
weekend.

Rip currents/surf: with the offshore flow today have trended
towards a low risk of rip currents followed by a significant
increase in surf late tonight into Wednesday to 6 to 9 feet and
expect the need for a high surf advisory with the next forecast
package along with a high risk of rip currents. The onshore flow
will continue at least a moderate to high risk of rip currents
through the entire week. The beach erosion during the high tide
Wednesday at beach conditions could be significant and another
reason for the coastal Flood Watch issuance.



Fire weather...

Much drier air will advect into the area Wednesday. Afternoon relative humidity
levels will fall below 30 percent over interior portions of the
area. However, winds are expected to be in a decreasing trend.



Hydrology...

Offshore flow today should allow for water levels in the St Johns
River basin to remain below minor flood stages today although
elevated conditions will continue and have kept a "coastal flood
statement" in place prior to the "main event" following the cold
front as north to northeast winds at 25-30 knots late tonight will
push the Wed morning high tide cycle to potential moderate levels
with the latest petss guidance still supporting reaching water
levels of 2 to 3 ft above mhhw along the NE Florida coastline as the
latest numbers still reach 2.3-2.5 feet mhhw at Mayport and
2.5-2.7 feet at Fernandina Beach so have posted coastal Flood
Watch with this package that will need to be further refined by
the day shift. The southeast Georgia coast will likely see values in the 1.5
to 2.5 feet mhhw and a coastal flood advisory may need to be
posted there in later updates. Following the potential moderate
flooding on Wed, the onshore flow the remainder of the week may
lead to possible minor coastal flood events as we move slightly
further away from the full moon phase.

&&

Preliminary point temps/pops...

Amg 70 30 51 38 58 / 80 0 0 10 30
ssi 75 38 58 50 65 / 90 40 10 20 20
jax 80 38 59 50 69 / 90 20 10 20 20
sgj 81 49 65 58 73 / 70 40 10 30 40
gnv 80 40 60 51 72 / 50 10 0 10 10
ocf 81 45 64 55 75 / 40 10 0 10 20

&&

Jax watches/warnings/advisories...
Florida...coastal Flood Watch from Wednesday morning through Wednesday
afternoon for Clay-coastal Duval-coastal Flagler-coastal
Nassau-coastal St. Johns-inland Duval-inland Flagler-inland
St. Johns-Putnam.

Georgia...freeze watch from late tonight through Wednesday morning for
Appling-Atkinson-Bacon-Brantley-Clinch-Coffee-Echols-inland
Camden-inland Glynn-Jeff Davis-northeastern Charlton-
northern Ware-Pierce-southern Ware-Wayne-western Charlton.

Am...Gale Warning from 6 PM this evening to noon EST Wednesday for
coastal waters from Altamaha Sound to Fernandina Beach Florida
out 20 nm-coastal waters from Fernandina Beach to St.
Augustine Florida out 20 nm-coastal waters from St. Augustine to
Flagler Beach Florida out 20 nm-waters from Altamaha Sound Georgia to

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