Tornado in Florida, June 20, 2017

Area Forecast Discussion
National Weather Service Tallahassee FL
642 AM EDT Tue Jun 20 2017

.AVIATION [Through 12Z Wednesday]...

While we're confident about periods of rain at all terminals
through tonight, we're not as confident about the temporary +SHRA
(with accompanying low Vis/cigs) that are likely to develop at
times today in the deep tropical moisture. However, we do think
that KDHN and KECP are the most likely sites to get periods of
heavier rain, and we have these sites in low-end MVFR conditions
through the entire period. Elsewhere we have -RA and VFR
conditions.

&&

.PREV DISCUSSION [337 AM EDT]...

.NEAR TERM [Through Today]...

At midnight EDT the center of potential tropical cyclone 03L was
located in the central Gulf of Mexico, and moving to the NNW. While
this system had a broad, closed surface circulation, recent IR
satellite imagery indicated little organization in the convective
pattern. Vapor imagery and upper air data showed a large envelope of
abnormally-high PWAT content (2.4"+ over much of the Gulf) across
the Gulf of Mexico and Gulf Coastal states. When coupled with the
fairly weak but persistent Q-G forcing associated with the deep-
layer trough over the central Gulf of Mexico, it's not hard to see
why our local radars were virtually covered with rain.

On-and-off rain, mostly light, will be the rule across most of our
forecast area today. However, mesoscale enhancements will allow
bands of very high rain rates to develop, especially along and west
of a line from Tallahassee to Albany (which is where we posted a
Flood Watch). Multiple Weather STEM sites in the Tallahassee area
recently reported rain rates of 2-4 inches per hour, as the warm
cloud depths of 12-15k feet were more than enough to allow for
efficient warm rain processes.

While the 0-1 km bulk shear will be increasing across the FL
Panhandle and adjacent coastal waters later this afternoon, poor
buoyancy is likely to limit the overall threat of severe storms. Of
course the clouds and rain will keep high temperatures well below
average- in the upper 70a to lower 80s, except mid 80s at Valdosta
and Cross City where there may be less clouds and rain.

.SHORT TERM [Tonight Through Thursday]...

The main focus for this period will remain the track of Potential
Tropical Cyclone Three and its impacts for our area. Latest
guidance has come into better agreement regarding the track of the
system with most models converging on potential landfall locations
from southeastern TX to the central LA Gulf Coast. As an upper
level trough pushes westward and gradually weakens to the west of
the tropical system, an upper level ridge will build across much
of the Gulf and gradual intensification is expected over the warm
Gulf Waters. However, some shear will persist over the center of
the low and it is not expected to intensify beyond tropical storm
strength.

Potential flooding will remain the main threat for our area due to
periods of heavy rain throughout this period. A Flash Flood Watch
remains in effect until Thursday morning near and west of a line
from Tallahassee to Albany. Even with the center of the system
several hundred miles to our southwest and eventually west, a
persistent plume of deep layer moisture could impact our western
and central zones with PWAT values remaining well above 2" from
Wednesday through Thursday morning. Across SE Alabama and the
Florida Panhandle, PWAT values could potentially exceed 2.5"
during this time. However, latest guidance shows that the heaviest
band of rainfall is likely to remain west of our area. Several
inches of rain are still possible across the watch area though,
especially from Panama City northward to Dothan and points west.

Highs will remain cooler than normal on Wednesday under overcast
skies and periods of showers/thunderstorms, remaining in lower-mid
80s. As the system moves inland and farther to our west on
Thursday, some breaks in the clouds could lead to slightly warmer
conditions with highs in the mid-upper 80s. Lows will be in the
70s each day, warmest near the coast with lower 70s farther
inland.

.LONG TERM [Thursday Night Through Tuesday]...

A more typical summer pattern is anticipated late this week
through the weekend as the tropical system moves inland and
dissipates across the lower Mississippi Valley region from
Thursday night into Friday. Rainfall chances will decrease from
earlier in the week, but scattered showers and thunderstorms are
still possible each day, especially in the afternoon and early
evening across inland areas during peak heating/instability and
aided by sea breeze forcing. Chances of showers and storms could
be enhanced by a cold front moving southeastward toward our area early
next week, along with increasing upper level dynamics as a potent upper
trough is projected to move into the eastern CONUS during this
time. No relief from typical summer humidity and heat is
anticipated, though, as the front should stall out before it
reaches the Gulf early next week. Highs will range from the upper
80s to lower 90s each day with lows in the lower-mid 70s.

.MARINE...

A strengthening tropical system continues to move north-
northwestward across the central Gulf. Conditions will continue to
deteriorate across our area today, with strong winds and very
choppy seas resulting from a tightening pressure gradient to the
northeast of the tropical system. Tropical Storm Warnings remain
in effect for offshore zones west of the Apalachicola River, with
a Small Craft Advisory elsewhere through Thursday morning. Winds
and seas will gradually subside late in the week as the tropical
disturbance makes landfall west of our area and weakens/dissipates
inland.

.FIRE WEATHER...

Red flag conditions are not expected for the next several days.

.HYDROLOGY...

A Flash Flood Watch remains in effect until Thursday morning near
and west of a line from Tallahassee to Albany. Tropical moisture
to the east of the disturbance in the Gulf will impact our area
through this time, with very high rainfall rates possible in
stronger bands of showers and thunderstorms. Highest rainfall
totals are expected to be in the Florida Panhandle with forecast
totals ranging from 4-6", gradually decreasing farther to the
north and east. Locally higher amounts are possible in areas where
training of heavier bands occurs, and this could result in
isolated areas of flash flooding. River flooding is also possible
later in the week through the weekend as potential widespread
heavy rainfall causes rivers to rise.

&&

.PRELIMINARY POINT TEMPS/POPS...

Tallahassee   82  74  84  75  86 /  90  70  70  30  30
Panama City   80  75  83  77  84 / 100  80  80  40  40
Dothan        78  71  82  74  84 /  90  80  80  50  60
Albany        81  72  82  73  86 /  90  80  80  50  50
Valdosta      84  73  84  74  88 /  90  60  60  30  40
Cross City    85  75  86  74  89 /  60  60  40  30  30
Apalachicola  82  77  84  79  85 /  90  70  80  30  30

&&

.TAE WATCHES/WARNINGS/ADVISORIES...

FL...Coastal Flood Advisory until 8 PM EDT /7 PM CDT/ Wednesday for
     Coastal Bay-Coastal Dixie-Coastal Franklin-Coastal Gulf-
     Coastal Jefferson-Coastal Taylor-Coastal Wakulla-South
     Walton.

     Flash Flood Watch through Thursday morning for Calhoun-Central
     Walton-Coastal Bay-Coastal Franklin-Coastal Gulf-Coastal
     Wakulla-Gadsden-Holmes-Inland Bay-Inland Franklin-Inland
     Gulf-Inland Wakulla-Jackson-Leon-Liberty-North Walton-South
     Walton-Washington.

     High Rip Current Risk through Thursday morning for Coastal Bay-
     Coastal Franklin-Coastal Gulf-South Walton.

     High Surf Advisory until 8 AM EDT /7 AM CDT/ Thursday for
     Coastal Bay-Coastal Franklin-Coastal Gulf-South Walton.

GA...Flash Flood Watch through Thursday morning for Baker-Calhoun-
     Clay-Decatur-Dougherty-Early-Grady-Miller-Mitchell-Seminole-
     Thomas.

AL...Flash Flood Watch through Thursday morning for Coffee-Dale-
     Geneva-Henry-Houston.

GM...Small Craft Advisory until 8 AM EDT Thursday for Apalachee Bay
     or Coastal Waters From Keaton Beach to Ochlockonee River Fl
     out to 20 Nm-Coastal Waters From Ochlockonee River to
     Apalachicola Fl out to 20 Nm-Coastal waters from Suwannee
     River to Keaton Beach out 20 NM-Coastal waters from
     Apalachicola to Destin FL out 20 NM-Waters from Suwannee
     River to Apalachicola FL from 20 to 60 NM.

     Tropical Storm Warning for Waters from Apalachicola to Destin FL
     from 20 to 60 NM.

&&

NEAR TERM...Fournier
SHORT TERM...Lahr
LONG TERM...Lahr
AVIATION...Fournier
MARINE...Lahr
FIRE WEATHER...DVD
HYDROLOGY...Lahr