Area Forecast Discussion
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FXUS62 KTAE 180139
AFDTAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
939 PM EDT Thu Apr 17 2014

...Heavy Rain over the Gulf of Mexico will move northeast
overnight...

.Near Term [Through Tonight]...
Significant storm system is taking shape this evening over the
central and eastern Gulf of Mexico. Expansive area of deep
convection has blossomed over the central Gulf in association with
the approaching shortwave. At the same time, intensifying region
of isentropic lift is generating an expanding rain shield across the
northeastern Gulf. Even further east, weaker isentropic lift
coupled with some elevated instability has allowed for showers and
isolated thunderstorms to develop over Apalachee Bay into the
central Big Bend this evening, a few hours earlier than previously
forecast.

As the upper shortwave continues to move east overnight, low
pressure will deepen over the central Gulf, with increasing
southerly flow riding up and over the strong surface ridge parked
along the eastern seaboard. This will expand the region of strong
isentropic lift northward into the Panhandle and Big Bend
producing a large expanse of moderate to occasionally heavy
rainfall.

Have increased the PoPs this evening for coastal areas to account
for the earlier onset of rainfall. Otherwise, the forecast remains
on track through the remainder of the night. Rainfall totals by
sunrise will likely exceed 1 inch for coastal areas of the
Panhandle.

&&

.Aviation...
[Through 00Z Saturday] Expect MVFR conditions across the area by
04z as ceilings continue to lower in advance of the approaching
storm system. Before sunrise, expect widespread heavy rain to
overspread the area with IFR conditions likely both due low
visibilities and ceilings. Conditions will trend back toward MVFR
late in the afternoon, especially at ECP/DHN as the heavier rain
starts to move away from those terminals after 20z.

&&

.Marine...
Winds and seas are on the increase this evening as developing low
pressure over the central Gulf works to tighten the gradient over
the coastal waters. Buoy south of Panama City recently reported 27
knot sustained winds with gust to 31 knots and 10 foot seas. With
this observation, along with general increase in forecast winds
from much of the guidance, have bumped the winds up a few knots
for the remainder of the overnight hours into Friday morning. This
necessitates expanding the Gale Warning to the eastern offshore
waters, and extending the Small Craft Advisory over the nearshore
Big Bend waters.

&&

.Prev Discussion [258 PM EDT]...

.Short Term [Friday Through Saturday Night]...
The first half of this period will be marked by heavy rain and
likely flooding. Aloft...Fri morning begins highly amplified with
ridging over Wrn states and extreme Wrn Atlc. In between...exists an
upper trough the result of srn/Nrn stream merging with a low over
Wrn Gulf. During the day...a strong shortwave begins to cutoff from
Nrn stream flow and develops a low that closes over Srn AL by
sundown. This will induce significant divergent flow over Nrn Gulf
of Mex. Low then advances Ewd to Ern seaboard Sat aftn and then
offshore at night with upper ridging building into the forecast area
overnight.

At surface...In response to above upper trough/low...assocd low had
already developed in Wrn Gulf with warm front ESE across Cntrl FL.
By sunrise Fri...intensifying closed low lifts Newd to around 100
miles south of Pensacola with front lifting further Nwd. Under
cutoff upper low...surface reflection slows down and with assocd
large stratiform shield of moderate to heavy rain begins to
strengthen and inch Newd. By sundown...upper low and surface
reflection phase and become vertically stacked and along with
lifting warm front quasi-stnry across FL Big Bend. Fortunately...
another SRN stream anomaly will be propagating EWD into the Wrn
Gulf overnight Friday, keeping a rather steady west wind aloft and
allowing the surface low to gradually drift away from land into the
Wrn Atlc by mid-morning Saturday. In its wake a ridge will
build in.

The forecast will focus on the combination of upper/lower features
and their impact on heavy rain and flooding. Models have come into
better agreement with the quicker GFS still a 6hr outlier. Area
soundings during Fri shows totally saturated nearly uni-directional
SSW profiles with PWATs around 1.8 inches. They are in agreement
that widespread heavy rains will overspread our local area Fri into
Fri eve, further aggravating ongoing river flooding with potentially
significant impacts. At this time it appears as though 3 to 4 inches
of rain will be common across SE AL, south Georgia, and north FL.
With average amounts that high, confidence is increasing that
isolated locations could pick up anywhere between 4-6 inches. That
being said, this rainfall will likely fall over an extended period
of time resulting in, for the most part, slow water rises. For that
reason, a more general Flood Watch remains in effect as opposed to a
Flash Flood Watch. However, the flash flooding potential is non-zero
and will be highest near rivers currently running at high levels and
in our more urban locations.

With regard to strong to severe weather...guidance with better
chance that with previous runs. On the one hand...extensive cloud
shield should  weak lapse rates aloft and we will have saturated
soundings. However any diurnal heating should have modest impact on
cape. Also approaching low should yield and increase in low and deep
layer shear. so although overall risk not high...cant discount
strong to an even isold severe storm if all ingredient come
together. The focus will be across mainly the extreme SE Big Bend of
Florida and adjacent waters in the afternoon. 100% chance of rain.
Under cloudy and rainy skies...high temps will struggle to reach 60
across much of SE AL and Srn Ga with areas of SE Big Bend reaching
to around 70.

High Risk of Rip Currents from Walton to Franklin Counties in effect
through Fri Eve. Possible coastal flooding issues will be addressed
tonight.

By Friday night, the heavy rain threat will have diminished, though
wrap around light showers will continue on the back side of the
departing low pressure until it has moved far enough east. Will go
with 30-80% SW-NE POP gradient. A 20-40% chance of rain remains for
Ern counties Sat morning but areas should be rain free by eve.
Expect lows Fri night from near 50 Nrn tier GA counties to near 60
SE Big Bend..and in the mid 50s everywhere Sat night. Highs Sat will
range from low-mid 70s in relatively cloud free west to mid 60s over
cloudy NE Tier GA counties closest to departing low.


.Long Term [Sunday Through Thursday]...
By Sunday, upper and surface ridge build into the region. By Monday
night...next weak trough and shortwave moves into Gulf region with
weak zonal flow across local area. A surface low well to our NW
brings a weak front to the Nrn Gulf before retreating back Nwd on
Wed. This will bring a slight chance of rain and isold thunderstorms
to the NRN counties Tues and Tues night followed by drying trend.
Throughout the entire period, both high and low temps will shows a
gradual warming trend. Inland highs Sun in the mid to upper 70s will
rise to the mid 80s Wed and Thurs. Inland Lows Sun night in the low
to mid 50s will rise by Thurs night to the low 60s.


.Fire Weather...
Low level moisture will quickly increase across the region with a
wetting rain expected across the entire region from late tonight
through Friday night. Drier and breezy conditions will then arrive
for most of the weekend. However, it does not appear that RH will
get low enough to be concerned about red flag criteria, especially
with the wet fuels.


.Hydrology...
We continue to be on track for a moderate to heavy rainfall event
across much of the forecast area Friday and into Friday Night.
Rainfall totals of 2 to 3 inches are expected to be fairly common,
with higher amounts perhaps up to 5 to 6 inches will be possible.
In general, the rivers most likely to flood and have higher
impacts will be in the Florida Panhandle and Big Bend where flows
are already somewhat elevated. Where the heaviest rain falls,
there should also be other flooding on smaller streams and creeks,
as well as areas of high water in low-lying areas and fields.

A more detailed hydrology discussion is available on our ESF
(Hydrologic Outlook) product, which can be found here:

http://www.srh.noaa.gov/product.php?site=NWS&product=ESF&issuedby=TAE

The most up-to-date river forecast information can always be found
on our AHPS page (below).

http:/water.weather.gov/ahps2/index.php?wfo=tae.

&&

.Preliminary Point Temps/PoPs...

Tallahassee   59  65  52  70  53 /  90 100  60  30  10
Panama City   60  65  55  73  57 / 100 100  40  10  10
Dothan        55  60  51  72  52 / 100 100  60  30  10
Albany        54  60  50  68  52 /  80 100  70  40  10
Valdosta      57  66  53  65  53 /  60 100  70  40  20
Cross City    62  73  59  69  53 /  60 100  60  30  20
Apalachicola  62  66  55  71  58 /  90 100  40  20  10

&&

.TAE Watches/Warnings/Advisories...

FL...Flood Watch from 2 AM EDT /1 AM CDT/ Friday through late Friday
     night for Calhoun-Central Walton-Coastal Bay-Coastal Dixie-
     Coastal Franklin-Coastal Gulf-Coastal Jefferson-Coastal
     Taylor-Coastal Wakulla-Gadsden-Holmes-Inland Bay-Inland
     Dixie-Inland Franklin-Inland Gulf-Inland Jefferson-Inland
     Taylor-Inland Wakulla-Inland Walton-Jackson-Lafayette-Leon-
     Liberty-Madison-South Walton-Washington.

     High Rip Current Risk through Friday evening for Coastal Bay-
     Coastal Franklin-Coastal Gulf-South Walton.

GA...Flood Watch from 2 AM EDT Friday through late Friday night for
     Baker-Ben Hill-Berrien-Brooks-Calhoun-Clay-Colquitt-Cook-
     Decatur-Dougherty-Early-Grady-Irwin-Lanier-Lee-Lowndes-
     Miller-Mitchell-Quitman-Randolph-Seminole-Terrell-Thomas-
     Tift-Turner-Worth.

AL...Flood Watch from 1 AM CDT Friday through late Friday night for
     Coffee-Dale-Geneva-Henry-Houston.

GM...Small Craft Advisory until 8 PM EDT Friday for Apalachee Bay-
     Coastal waters From Ochlockonee River to Apalachicola FL
     out to 20 NM-Coastal waters from Suwannee River to Keaton
     Beach FL out 20 NM.

     Small Craft Advisory until 2 AM EDT Friday for Coastal waters
     from Apalachicola to Destin FL out 20 NM-Waters from
     Suwannee River to Apalachicola FL from 20 to 60 NM-Waters
     from Apalachicola to Destin FL from 20 to 60 NM.

     Gale Warning from 2 AM to 8 PM EDT Friday for Coastal waters
     from Apalachicola to Destin FL out 20 NM-Waters from
     Suwannee River to Apalachicola FL from 20 to 60 NM-Waters
     from Apalachicola to Destin FL from 20 to 60 NM.


&&

$$

NEAR TERM...CAMP
SHORT TERM...BLOCK
LONG TERM...BLOCK
AVIATION...GODSEY
MARINE...CAMP
FIRE WEATHER...DVD
HYDROLOGY...LAMERS








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