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Area Forecast Discussion

774
FXUS62 KTAE 030033
AFDTAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
833 PM EDT SUN AUG 2 2015

.Near Term [Through Tonight]...

The 6 pm EDT regional surface analysis showed a weak, broad low
pressure system over Apalachee Bay, with a 1009 mb center near
the coast at the Taylor-Dixie County border. This low had been
drifting southeast very slowly for the past 6 to 12 hours. Vapor
imagery and upper air data showed dry, brisk northwest winds aloft
over this system, which seemed to be inhibiting development into a
tropical system. There was a quasi-stationary front from the LA
coast through southeast AL and across central GA. East of the
front the boundary layer remained quite moist, and there were
still a few north-south oriented convective convergence bands
translating slowly westward across our forecast area. We expect
these to diminish by midnight, but showers and thunderstorms will
continue across Dixie County.

All of the latest NWP guidance takes the surface low inland later
tonight, with a diminishing chance of rain across the water-logged
Taylor and Dixie County coasts. It`s tempting to drop some of the
Flash Flood Watch, but we think it`s wise to make sure this system
moves inland first. Also, deep moist convection with these types
of systems tends to peak overnight, so we`ll delay the watch
cancellation and let the next shift take another look.

There was a narrow, relatively strong pressure gradient south of
the surface low center, generating a decent fetch of rather strong
southwest winds. They were driving seas to well above guidance (up
to 9 ft at buoy 42036) and tides 2 ft above normal. We have not
issued a Coastal Flood Advisory because low tide is approaching
through midnight, but tides will need to be monitored later when
the high tide begins to approach.

&&

.Aviation...

[Through 00Z Tuesday]...Scattered SHRA/TSRA will diminish by 4Z.
Generally VFR conditions are expected until low cigs develop
around KVLD, then spread into KABY and KTLH by dawn Monday. These
cigs will gradually lift my mid to late morning, followed by VFR
conditions. Isolated TSRA are expected around KTLH and KVLD Monday
afternoon, but PoPs are a little too low to include them in this
forecast package,

&&

.Prev Discussion [416 PM EDT]...

.Short Term [Monday Through Tuesday Night]...

The area of low pressure along the stalled frontal boundary will
slowly dissipate and continue to push eastward, with the front
exiting the area through Monday evening. The primary forcing for
convection will be from this system, keeping chances for showers
and thunderstorms highest in the eastern Big Bend and further
south and east of our warning area. With a weak afternoon
seabreeze front, there will also be a 30-40% chance for showers
and thunderstorms across north Florida in the afternoons,
primarily along and south of I-10. The heaviest rain will be over
as we head into the work week, however, even moderate rain on top
of already supersaturated soil may exasperate or cause new
flooding issues in isolated areas.

Highs will stay in the low to mid 90s where rain chances are
highest. Further north and west of the decaying frontal system in
southeast Alabama, drier air will be in place with dewpoints
dropping into the mid-upper 60s, which will keep any convection
isolated, but allow afternoon temperatures to soar into the upper
90s. Overnight lows will dip into the low to mid 70s.


.Long Term [Wednesday Through Sunday]...

After the decaying front exits our area, we will have a few drier
and slightly cooler days with highs in the low 90s, lows in the low-
mid 70s, and normal summertime chances for scattered storms in the
afternoon. Heading into next weekend however, models are suggesting
another frontal system may push southeastward into the forecast area
and stalling again, similar to what we`ve seen this weekend. For
now, bumped chances to 40-50% along the Florida Big Bend and into
south central Georgia.


.Marine...

As an area of low pressure in the northeastern Gulf weakens and
moves east through Monday, the pressure gradient will weaken and
advisory level winds and seas will lower. A brief period of
cautionary winds will be possible Monday, then winds and seas will
remain below headline criteria for the remainder of the period.


.Fire Weather...

No fire weather concerns through this week.


.Hydrology...

Rainfall totals since Friday morning across Southeastern Taylor and
Dixie Counties were in the 10 to 15 inch range as estimated by radar
with a couple of higher totals near 18 to 19 inches. A couple of
observations in excess of 12 inches were also reported in Dixie
County in the last 24 hours. Widespread areal flooding is common
across these areas, as natural drainage systems are overcome by
excess runoff. Unfortunately, little if any improvement in the flood
situation is expected tonight. With the weak surface low still west
of the Big Bend, expect rain to continue overnight, though not as
extreme as Saturday. Another 2 to 3 inches with isolated heavier
totals is expected.

The primary focus for river flooding is on the Steinhatchee River
where modest rises continue. With basin areal totals in the 9 to 12
inch range in the last 48 hours, there are some strong similarities
with this event and the 5/17/14 flood event. The river is forecast
to crest at 16.5 feet on Monday, which is moderate flood stage.

Elsewhere, river flooding is not anticipated. The bulk of the heavy
rainfall in the Suwannee Basin fell south of Rock Bluff. Though some
minor rises have occurred at Wilcox and Manatee Springs, this
portion of the river will remain safely below action stage. With the
increased runoff from further upstream and tides running about a
foot above normal at the Suwannee River Entrance, the Fowlers Bluff
point will likely reach action stage at each high tide cycle through
Monday afternoon.

&&

.Preliminary Point Temps/PoPs...

Tallahassee   75  97  74  96  75 /  30  40  30  40  40
Panama City   78  91  78  90  79 /  30  30  20  30  30
Dothan        73  98  73  97  75 /  20  10  10  20  20
Albany        74  97  73  98  75 /  20  10  10  20  10
Valdosta      73  95  74  98  75 /  20  20  20  40  40
Cross City    75  90  75  92  75 /  50  50  30  40  30
Apalachicola  78  92  78  91  78 /  50  30  30  40  30

&&

.TAE WATCHES/WARNINGS/ADVISORIES...
FL...FLASH FLOOD WATCH until 8 AM EDT Monday FOR Coastal Dixie-
     Coastal Taylor-Inland Dixie-Inland Taylor-Lafayette.

     HIGH RIP CURRENT RISK until 10 PM EDT this evening FOR Coastal
     Franklin.

GA...NONE.
AL...NONE.
GM...SMALL CRAFT ADVISORY until 5 AM EDT Monday FOR Coastal waters
     from Suwannee River to Keaton Beach out 20 NM-Waters from
     Suwannee River to Apalachicola FL from 20 to 60 NM.

&&

$$

NEAR TERM...FOURNIER
SHORT TERM...MOORE
LONG TERM...MOORE
AVIATION...FOURNIER
MARINE...MOORE
FIRE WEATHER...FOURNIER
HYDROLOGY...WESTON



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