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Area forecast discussion 
National Weather Service Jacksonville Florida
510 am EDT Friday Apr 18 2014

..Flood Watch through early Saturday morning region-wide...
..Strong to severe thunderstorms possible late this afternoon and
evening in north central Florida...

Currently...
early morning surface analysis depicts strong ridging (1042
millibars) centered over the Canadian maritime region...wedging
southwestward down the U.S. Eastern Seaboard.
Meanwhile...cyclogenesis occurred overnight over the eastern Gulf
of Mexico...with a 1012 millibar low pressure center south of the
Florida Panhandle moving slowly northeastward. A developing warm front
is pushing northward from South Florida. Aloft...a potent
shortwave trough was diving through the arklatex region...creating
significant divergence over the eastern Gulf of Mexico that has
fostered the development of a large mesoscale convective system
(mcs) over the warm loop current waters that is progressing slowly
eastward. Strengthening southerly flow over this convective plume
was pushing a large area of moderate to heavy rainfall into the
Florida Panhandle and Big Bend region...with lighter showers
moving quickly northward through the Suwannee Valley and northeast
Florida. Temperatures and dewpoints ranged from the middle 50s in
interior southeast Georgia to the 60s elsewhere.

Short term (today through Sunday night)...
the potent shortwave over the Southern Plains will dig east-
southeastward towards the Gulf Coast...which will push low pressure
towards the Florida Big Bend coast this evening. The warm front over
South Florida will lift northward towards Interstate 10 this afternoon.
Model soundings depict strong low-level convergence coincident
with a plume of deep moisture (pwats nearing 2 inches)
overspreading our region as the day progresses. Strengthening
middle-level southerly flow will spread moderate to heavy rains over
interior southeast Georgia and the Suwannee Valley by late morning...with
activity pushing eastward towards coastal locations by late
afternoon. The strongest forcing will likely occur along and just
north of the warm frontal boundary. The weather prediction center
has thus indicated a moderate risk for excessive rainfall over
southeast Georgia...with a slight risk along the I-10 corridor in
northeast Florida. Model soundings suggest that enough instability will
develop in the warm sector over north central Florida along with a
veered low-level wind profile for strong to severe thunderstorm
development this afternoon...as outflow from the ongoing Gulf mesoscale convective system
moves across the peninsula. Damaging wind gusts and isolated
tornadoes are the primary threats with this activity. This threat
may extend into the evening hours...as low pressure slowly
approaches our region. Highs in north central and northeast Florida
will surge into the 70s this afternoon as the warm front lifts to
near I-10...while highs in southeast Georgia remain in the middle/upper
60s.

The 06z/00z operational European model (ecmwf) maintain a slower solution than the
00z operational GFS...which would keep the threat for heavy rains
in place over southeast Georgia throughout the night. Widespread 2-4
inch rainfall totals are expected...especially along and north of
I-10...with 4-6 inch totals possible over southeast Georgia. Heavy
rains this evening may cause problems in coastal locations during
the late evening high tide cycle...particularly in flood prone
areas such as mccoys creek in downtown Jacksonville and low lying
areas of downtown Brunswick. The upper trough will cutoff later
tonight over southern Georgia...with a significant amount of wrap-
around moisture expected to develop as low pressure approaches the
Atlantic coast. Shower and thunderstorm coverage should decrease
from southwest to northeast over our Florida counties during the
predawn hours on Sat. Will leave the expiration time of the Flood
Watch at 5 am Sat...but this may need to be extended if slower
model solutions verify. Lows tonight will range from the 50s in
interior southeast Georgia and the Suwannee Valley to the 60s
elsewhere.

Sat & Sat night...deeper convection including thunderstorm activity
will depart offshore of the Atlantic coast early Saturday morning
with the surface low expected to be near the Georgia/Florida Atlantic
coast...and the upper level low over the Florida Panhandle/SW Georgia
region. Drier air is expected to wrap into the stacked low from
the south Sat which will gradually decrease shower chances from S
to north through Sat into Sat night as the low advances offshore. High
temperatures are expected to range from the middle/upper 60s over southeast Georgia on
the north-northwest side of the surface low...to the low/middle 70s over NE Florida
within the 'warm sector' under a warm and breezy west wind. Sat
night a cool and drier north-northwest wind will prevail as cloud cover
gradually decreases with min temperatures ranging from the low 50s inland
to near 60 coast.

Sun & Sun night...deep layer northerly flow will funnel southward
as the low departs farther offshore of the southeast Atlantic Seaboard
and surface high pressure wedges down the Lee of Appalachians over
central Georgia. Lingering light showers will move offshore by Sun
afternoon. Breezy north winds may near lake Wind Advisory conditions
near the Atlantic coast where sustained speeds will near 20g35mph.
High temperatures will range from near 70 over southeast Georgia to near 80 over NE
Florida. Sun night winds veer north-northeast as the ridge settles farther south
over Georgia and winds gradually decrease in speed. Temperatures will fall
into the low/middle 50s inland to near 60 coast under partly cloudy
skies.

Long term (monday through friday)...
mostly dry and near to slightly above climatology temperatures with mins in the
middle 50s to low 60s and highs in the upper 70s to lower 80s. A fast
moving short wave trough and weak surface front may bring a quick shot
of showers over southeast Georgia on Wednesday...but only advertised 20% chance of
probability of precipitation for southeast Georgia given weak forcing.

&&

Aviation...
deteriorating conditions expected over the next 12-18 hours as low
pressure approaches and crosses NE Florida. Prevailing MVFR conditions
are expected this morning with tempo IFR...then prevailing IFR
this afternoon and evening due to waves of moderate to locally heavy
rainfall. Over the next few hours...light showers will impact the
gnv and jax/ssi terminals. Strong NE flow sustained 15-20 kts with
gusts to 25 kts will develop after sunrise along the Atlantic
coast at crg/ssi...with slightly less speeds inland toward
vqq/gnv. Slight chance of thunderstorms this afternoon and tonight at
all terminals...but will leave out of the tafs for now.

&&

Marine...
low pressure developing over the eastern Gulf of Mexico will
approach the Florida Big Bend coast this evening...and will then
move slowly across our coastal waters on Saturday and Saturday
night. Strong onshore winds will persist in the near shore waters
today...with winds becoming southeasterly over the Florida waters this
afternoon. Strong thunderstorms will be possible late this
afternoon and through this evening in the Florida waters...with strong
wind gusts being the main threat. Winds and seas will briefly
diminish to caution criteria in the near shore waters tonight and
Saturday as low pressure approaches...with advisory level seas
persisting offshore. Periods of heavy rainfall are expected from
this afternoon through early Saturday. As the low pressure center
exits the offshore waters on Saturday night...a surge of northwest
to northerly winds will overspread the waters...with gale
conditions expected offshore by early Sunday and continuing into
Sunday evening. Near gale conditions will be possible in the near
shore waters on Sunday. A long fetch of northerly winds will build
seas to 9-12 feet offshore and 5-9 feet near shore on Sunday and
Sunday night. Winds and seas will gradually diminish by late
Monday.

Surf zone/rip currents: local reports indicate surf reaching 6-8
feet this morning...and thus a high surf advisory has been issued
through this evening....with a high risk of rip currents
continuing. Expecting surf to remain just below minor coastal
flood criteria during the morning high tide cycle...with tidal
departures approaching 2 feet. Bigger concern is during the
evening high tide cycle...when minor coastal flooding will become
more of a concern. This higher high tide combined with heavy
rainfall may cause localized flooding in the urbanized areas of
Jacksonville...Brunswick and St. Augustine.

&&

Hydrology...
widespread 2 to 4 inch storm rainfall totals by Saturday will push
river flooding into moderate category by early next week across
the Suwannee and Santa Fe River basins...while the remainder of
our river basins reach or remain in minor flood status.

&&

Preliminary point temps/pops...
amg 64 55 65 50 / 100 100 60 40
ssi 66 62 69 56 / 100 100 60 40
jax 73 61 71 55 / 100 100 50 40
sgj 73 63 71 58 / 100 100 50 30
gnv 75 60 72 53 / 100 100 40 30
ocf 77 61 74 55 / 100 100 40 20

&&

Jax watches/warnings/advisories...
Florida...Flood Watch from noon EDT today through late tonight for Alachua-
Baker-Bradford-Clay-Columbia-Duval-Flagler-Gilchrist-
Hamilton-Marion-Nassau-Putnam-St Johns-Suwannee-Union.

High rip current risk through this evening for Duval-Flagler-
Nassau-St Johns.

High surf advisory until 7 PM EDT this evening for Duval-Flagler-
Nassau-St Johns.

Georgia...Flood Watch from noon EDT today through late tonight for Appling-
Atkinson-Bacon-Brantley-Charlton-Clinch-coastal Camden-
coastal Glynn-Coffee-Echols-inland Camden-inland Glynn-Jeff
Davis-Pierce-Ware-Wayne.

High rip current risk through this evening for coastal Camden-
coastal Glynn.

High surf advisory until 7 PM EDT this evening for coastal
Camden-coastal Glynn.

Am...Small Craft Advisory until 6 PM EDT Monday for Altamaha Sound Georgia
to Fernandina Beach Florida 20 nm to 60 nm offshore-Fernandina
Beach to St Augustine Florida 20 nm to 60 nm offshore-St
Augustine to Flagler Beach Florida 20 nm to 60 nm offshore.

Small Craft Advisory until 6 PM EDT this evening for Altamaha
Sound Georgia to Fernandina Beach Florida out 20 nm-Fernandina Beach
to St Augustine Florida out 20 nm-St Augustine to Flagler Beach
Florida out 20 nm.

&&

$$

Nelson/enyedi