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000
FXUS62 KJAX 230838
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
438 AM EDT Tue May 23 2017

...LOCALLY HEAVY RAINFALL AND ISOLATED SEVERE STORMS POSSIBLE
THROUGH WEDNESDAY...

.NEAR TERM /Today and Tonight/...

Deep cyclonic flow will continue to dig into the area today, with
steady pressure falls and height falls. Deep moist southwest flow
will strengthen quite a bit today as a surface low rapidly moves
northeast from the Louisiana coast early this morning to the
midlands of South Carolina by late this afternoon. This pattern
will favor numerous to widespread showers and embedded
thunderstorms, but timing the details in this progressive pattern
is proving to be very difficult for today, especially across
northeast Florida. The temp forecast is also tricky due to
increased cloud cover and precipitation.

The biggest change for today will be the significant increase in
shear as a strong low level jet moves over the area, especially
across southeast Georgia where the NAM12 shows a LLJ of 50+ knots
this afternoon. Realized instability will be held in check but
will ultimately depend on how much warming takes place today.
Steady on and off showers/storms over Georgia will keep heating in
check there but MUCAPE values around 1500 J/KG combined with the
increased shear will be enough to support a chance for severe
storms, and SPC has all of southeast Georgia in a slight risk
today. Damaging wind gusts and locally heavy rainfall will be the
main threats. Enhanced thunderstorm wording has been added to the
forecast.

Higher Cape values will be possible near the Atlantic coast of
northeast Florida where the warmest temps are expected today. The
southwest flow will bring breezy conditions to the area today with
winds of 15 to 20 mph with occasional gusts up to 30 to 35 mph
possible. This will ensure that there will be no Atlantic coast
seabreeze today.

The steadiest rains will occur across portions of southeast
Georgia (closer to the surface low) as storms train across the
area through the day. Widespread 1 to 2 inches is expected there
today and tonight.

Precipitation chances across northeast Florida is a little tougher
to figure out, but the general thinking is that scattered bands of
elongated showers/storms will begin to track from the Gulf by late
morning. This activity will quickly move northeast across the area
and should become more numerous during the afternoon hours. Strong
gusty winds will be possible with this activity in Florida. Heavy
rainfall will be held in check in northeast Florida today due to
the rapid movement of this activity. Locally heavy rainfall though
will occur if/where storms train.

The more widespread rains/embedded storms are expected to shift
south and focus across northeast Florida tonight with heavy
rainfall possible after midnight, especially across the Suwannee
River Valley where a widespread 1 to 2 inches of rain is expected.
Locally higher amounts can be expected.

.SHORT TERM /Wednesday through Thursday Night/...

Upper level trof/low centered over Missouri will extend into the
Gulf of Mexico driving a frontal boundary into the western Florida
Panhandle and western Georgia early in the day. Deep layer
southwesterly wind and speed shear will occur with surface winds
strengthening at 15-25 mph with some higher gusts while higher
pre-frontal moisture overspreads the area with precipitable water
values 1.8" to 2.0".

A band of convection is likely to be ongoing Wednesday morning
across the northeast Gulf and into the Suwanee Valley and further
east and north. The band of convection ahead of the front could
produce strong to severe storms. The sounding profile suggests a
nearly saturated atmosphere, and significant rainfall is possible,
especially in training bands. An additional 1-3 inches of rain
areawide is expected through Wednesday night, with locally higher
amounts. A Flood Watch could be necessary for portions of the
region for Wednesday and Wednesday night. Due to ample cloud cover
and ongoing rainfall, instability does decrease, highs are only
forecast to be in the upper 70s to lower 80s, but shear does
increase as the trough approaches, with SFC to 3km shear values at
30-40 knots. The wind profile will be unidirectional with ample
CAPES of 1200-1600 J/kg, and 0-1km helicity will increase to
150-250 m2/s2. With this said, a couple rounds of strong to severe
weather will be likely across the region throughout the day, with
linear and supercell modes possible. The main threats are
forecast to be wind gusts of 45 to 65 mph, and 1" hail with 500mb
temps cooling to -10C. An isolated tornado cannot be ruled out due
to the strengthening low level wind field. A band of convection
is likely to develop along the front, with the main threat being
damaging winds overnight. SPC has the entire region in a Slight
Risk for Wednesday and Wednesday night.

The convective activity will slowly progress southeast through
the evening and into the overnight hours, clearing the southeast
portions of the region by daybreak Thursday. Some clearing
expected over inland southeast Georgia and the western Suwannee
Valley by the predawn hours on Thursday as cold front pushes into
north central Florida. Lows will fall to the lower 60s interior
southeast Georgia, and mid to upper 60s elsewhere.

Thursday and Thursday Night: The upper trough axis shifts through
the region by Thursday afternoon, with a surface cold front well
ahead pushing east-southeast through the North Central southern
tier zones by early morning. The heavy rainfall threat will also
end Thursday morning behind the front. Drier air will filter into
the region through the day as the cold front pushes southward,
with much more pleasant dewpoints in the 50s areawide by
afternoon. Friday morning lows will be cooler in the mid/upper 50s
inland and the low 60s along the coast, around 5 degrees below
normal.

.LONG TERM /Friday through Tuesday/...

Dry conditions are forecast through Saturday. Upper level heights
will build through Saturday from the southwest. The upper ridge
axis will then settle across central Florida Sunday and Monday,
with weak upper troughing pushing into the region early next week.
At the surface, the ridge axis will settle across central Florida
through the period, with light west to southwest flow prevailing.
A weak frontal boundary is forecast to stall north of the region
Monday night and Tuesday. Low rain chances are forecast late in
the weekend and early next week, with the best chances across
southeast Georgia closest to the boundary. Highs will rebound
Friday, with highs returning to above normal values in the upper
80s to lower 90s. Lows will be climb back into the upper 60s to
lower 70s.

&&

.AVIATION...

VFR should prevail through at least the morning hours and then
showers/storms will increase from the southwest through the
afternoon hours. Timing this activity is difficult at this time,
but look for amendments throughout the day as we gain a better
understanding of the timing. Showers/storms will move fairly
quickly to the northeast today with brief restrictions in heavy
rain and gusty winds with each individual cell. Multiple storms
however may move across the same areas as we go through the
afternoon hours. A more persistent widespread rain will be
possible tonight with some embedded thunderstorm activity, and
this will bring potential for longer periods of restrictions.

&&

.MARINE...

Southwesterly winds will bring SCEC conditions today. Winds will
continue to increase tonight with SCA conditions expected to begin
across the outer waters by late this evening. Winds will continue
to increase on Wednesday and especially Wednesday night as a
strong late season cold front approaches the area. Gusts to gale
force can be expected Wednesday night and a Gale Warning may be
forthcoming. Numerous showers/storms with gusty winds and heavy
rainfall will move offshore into the waters over the next two
days. The cold front will finally move through early Thursday
morning and conditions will steadily improve during the day.

Rip Currents: Low Risk due to developing offshore flow.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  82  70  79  62 /  90  50  90  40
SSI  86  73  80  69 /  70  60  90  70
JAX  88  72  81  66 /  70  70  90  70
SGJ  89  73  83  67 /  50  60  90  80
GNV  86  72  81  66 /  70  80  90  70
OCF  87  73  82  68 /  50  70  90  70

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...None.
AM...Small Craft Advisory from 11 PM this evening to 2 PM EDT
     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.

&&

$$

Shuler/Kennedy/