Flash Flooding and Flooding in Florida, August 16 to 19, 2019

Area Forecast Discussion
National Weather Service Tallahassee FL
602 AM EDT Fri Aug 16 2019

...FLOOD WATCH IN EFFECT FOR THE SOUTHEAST BIG BEND THROUGH
SATURDAY...

.AVIATION...

[Through 12z Saturday] Early morning patchy fog and low ceilings
will give way to VFR conditions by mid-morning. Scattered afternoon
showers and thunderstorms are expected around TLH and VLD.

&&

.PREV DISCUSSION [310 AM EDT]...

.NEAR TERM [Through Today]...

An interesting forecast is shaping up for the southeast big bend
starting today. The current upper level analysis shows a 500 mb vort
max near the Dixie county coast with convection associated with it.
A deep tropical airmass is in place across the southeast big bend
with a plume of precipitable water values in excess of 2.5 inches.
Meanwhile, much drier air behind a weak frontal boundary exists just
to the north. Guidance indicates that the upper level vort max will
move slowly over the next 24 hours. Meanwhile, the plume of deep
tropical moisture will remain in place across the southeast big bend
with southwesterly surface flow increasing surface convergence along
the coast. Thus, there are ample forcing mechanisms for deep
convection today considering the surface convergence, upper level
vort max, and stalled front just to the northwest. In addition, the
overall steering flow is quite weak and favors training convection.
This evidence favors heavy rainfall potential across the southeast
big bend, and given that portions of the area saw several inches of
rain on Thursday, conditions are becoming more saturated and a flood
watch has been issued. Rain chances taper off considerably the
farther northwest one goes given the drier airmass to the northwest.

.SHORT TERM [Tonight Through Sunday Night]...

An upper trough remains over the far southern Big Bend counties as
of 00z tonight with shortwaves riding along it. This will keep near
continuous rain in the forecast for that region overnight. By
morning, showers and thunderstorms will also form slightly offshore
aided by a convergence boundary that develops overnight. Enough
elevated instability will remain for a few rumbles of thunder.

The front will be well back to the west on Saturday but the remnant
boundary will still be aided by moderately strong shortwaves aloft.
The best forcing will generally be along the coast and up the
eastern parts of our CWA border, keeping numerous to widespread
showers and thunderstorms in those areas. Although we lose daytime
heating Sat night, the wave lifts north so the showers will continue
in generally the same region as the daytime. With the return of
stronger southerly flow on Sunday, we see more of a sea breeze type
pattern setting up. This will also be aided by a weak upper trough.
Showers/storms will form offshore and progress inland during the
day. Steering flow is still somewhat weak so inland extent will be
determined by outflow boundaries. Storms will generally dissipate
overnight outside of the immediate coast.

Soundings are quite saturated both Saturday and Sunday with PW
values over 2.25." Even with continuous cloud cover, daytime heating
will allow for 1500-200 J/KG of CAPE to develop. Sunday CAPE
profiles are a bit thicker so we should see slightly deeper
storms. Neither day looks impressive enough for severe storms but
locally heavy downpours are a given. With the continuous rainfall
the last few days, the ground is fairly saturated and flooding of
low lying areas could occur quickly. The Flood Watch for Taylor,
Lafayette and Dixie counties will go through 00z Sunday for now,
but that could be extended.

Highs will be in the lower to mid 90s still on Saturday but with a
brief return of west-northwest winds and increased clouds/rain,
highs Sunday will drop to the mid 80s.

.LONG TERM [Sunday Night Through Friday]...

A mid level ridge starts to build in from the east on Monday with an
upper trough moving through the upper midwest. Locally, a weak
shortwave looks to get trapped between the two systems. This,
combined with southerly flow and continued PW values around 2
inches, will lead to a rainy and unstable week. Scattered to
numerous showers and thunderstorms are expected each day although
exact location and timing is too far out to determine. Highs will be
in the 80s Mon/Tue and back into the lower 90s Wed-Fri.

.MARINE...

Winds will generally be out of the southwest through the period
with speeds around 10 to 15 knots. Slightly higher speeds are
possible through Saturday and in and around any thunderstorms.
Seas will increase with the increasing winds, around 3 to 5 feet
by Saturday night before decreasing below 3 to 4 feet on Sunday.
Scattered to numerous showers and thunderstorms are possible over
the waters each day.

.FIRE WEATHER...

Red flag conditions are not expected for the next several days with
relative humidity values remaining above critical levels.

.HYDROLOGY...

Forecast storm total rainfall from the WPC is in the 5-8 inch range
across portions of Dixie, Taylor, and Lafayette counties through
Sunday. Given that portions of this area have already seen 3-5
inches of rainfall, the ground is gradually becoming more saturated.
This additional rainfall may result in some flooding of roads and
low lying areas, thus a flood watch has been posted. We'll have to
keep an eye on the Steinhatchee River as well, although it's
starting from low flow, so it can handle several inches of rain
before river flooding starts to become a threat. Elsewhere, 2-4
inches of rain is expected across far southern Georgia and the
remainder of the Florida panhandle and big bend. These expected
amounts should not result in any significant flooding for those
areas.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not requested. However, spotters are always
encouraged to safely report significant weather conditions when they
occur by calling the office or tweeting us @NWSTallahassee.

&&

.PRELIMINARY POINT TEMPS/POPS...

Tallahassee   92  75  90  73  87 /  50  40  60  40  80
Panama City   89  77  88  76  86 /  40  50  60  50  70
Dothan        95  73  94  73  87 /  10  10  40  20  70
Albany        96  74  94  74  89 /  20  10  50  20  70
Valdosta      89  73  89  72  87 /  60  40  60  30  70
Cross City    84  75  85  74  87 /  90  70  70  50  50
Apalachicola  88  78  87  77  86 /  70  50  70  60  60

&&

.TAE WATCHES/WARNINGS/ADVISORIES...
FL...Flood Watch through Saturday evening for Coastal Dixie-Coastal
     Taylor-Inland Dixie-Inland Taylor-Lafayette.

GA...None.
AL...None.
GM...None.
&&

NEAR TERM...DVD
SHORT TERM...LN
LONG TERM...LN
AVIATION...DVD
MARINE...LN
FIRE WEATHER...DVD
HYDROLOGY...DVD

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TALLAHASSEE FL
629 AM EDT FRI AUG 16 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0628 AM     HEAVY RAIN       1 SSW STEINHATCHEE      29.66N 83.39W
08/16/2019  M7.38 INCH       DIXIE              FL   MESONET

            WUNDERGROUND SITE KFLSTEIN5 HAS MEASURED
            7.38 INCHES OF RAIN SINCE THURSDAY WITH RAIN
            CONTINUING.

&&

DVD