STORM2K

Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
355 PM EDT Sat May 26 2018

...Stormy With Locally Heavy Rain And Flooding Possible Through The
Holiday Weekend...
...Hazardous Marine And Beach Conditions Through The Holiday
Weekend...

.SHORT TERM (Tonight - Sunday)...
Tropical moisture being advected northward from Sub-Tropical Storm
Alberto will keep a moist and unstable environment over the region
for the next 36 hours. TS Alberto is located just to the west of
Cuba and is expected to move north-northwest into the Gulf of Mexico
moving west of Florida on Sunday and approaching the northern gulf
coast by Monday. The primary effects we will see from this storm in
west central and southwest Florida will be heavy rainfall, isolated
thunderstorms, gusty winds, and dangerous marine conditions. More on
that in the marine discussion.

Currently, light rainshowers continue to spread over west central
and southwest Florida as well as the gulf coast waters. Latest radar
imagery is showing the bands of showers spreading from southern
Floriida and approaching the Nature Coast with only a few ticks of
lightning inside embedded thunderstorms primarily over the gulf
coast waters. The 18Z afternoon upper air sounding is continuing to
show abundant moisture with a PWAT of 1.92 inches. The afternoon
sounding is also showing a thick layer of east through southeast
winds from 500MB and below which will drive a southeast to northwest
shower/storm movement through the day. Latest HRRR guidance is
showing a persistent coverage of rainfall continuing through the
evening hours and into Sunday morning. It looks as if most of this
will be light-moderate rainshowers with a few embedded
thunderstorms. Zone forecasts and coastal forecasts will be updated
based off the next TS advisory around 21Z.

&&

.LONG TERM (Sunday night - Saturday)...
During Sunday night into Monday subtropical storm Alberto will be
moving north over the eastern Gulf, with the current official
forecast track from NHC moving Alberto onshore along the northern
Gulf coast late Monday night or early Tuesday morning. Abundant
tropical moisture (PW's aoa 2 inches) streaming north into the
region on a deep layered southerly wind flow on the eastern side of
Alberto will maintain high rain chances (Pops in the 60 to 80
percent range) across the entire forecast area through Wednesday,
with numerous to widespread showers and isolated storms (additional
rainfall amounts of 2 to 4 inches possible Mon-Wed) expected each
day, along with heavy rainfall which will continue the threat for
both areal and river flooding problems across the region, especially
in areas which see the training of the showers and storms.

With all of this moisture in place, rain chances will remain high
through the rest of the weekend. Of particular concern is that for
late tonight and Sunday, South Florida will lie under a region of
upper-level divergence to the east of the deepening mid/upper level
low pressure over the Gulf of Mexico associated with Alberto, as
well as increasing low-level convergence and wind fields around the
periphery of Alberto`s large-scale circulation. This synoptic setup
is conducive for bands of rain and a few embedded thunderstorms to
not only increase in coverage but also in intensity as they move
north across the area. The end result is that our flood threat will
increase beginning late tonight and continue through Sunday, and
possibly Sunday night as well. The Flood Watch will remain in place
at least through Sunday evening, and we will continue to closely
monitor the threat of heavy rain and flooding even into Monday as
Alberto continues to affect the northern Gulf coast.

Along with the increasing threat of flooding, the potential for
isolated tornadoes will increase late tonight in response to the
strengthening low-level wind profiles, helicity values and
increasing instability. The highest tornado threat appears to be
late tonight and Sunday over Southwest Florida, but notable as well
over Southeast Florida. This corresponds well with SPC`s marginal
risk area over all of South Florida.

UPDATE...
Raised rain chances overnight to nearly 100 percent as nearly
certain widespread rain will continue. Latest convective band is
pushing into far southern Florida nearly 1z and additional banding
is likely toward early morning. 0z RAOB indicates increasingly
favorable airmass for rotating updrafts as supplemented by HRRR
and other CAMs. Target time for enhanced tornado risk appears to
be 5z-13z, so will be continuing to closely monitor. SPC continues
with Slight Risk of tornadoes and damaging winds south and west of
a Naples to Miami line overnight, with Marginal Risk for remainder
of CWA. Flood Watch and Small Craft Advisory continues areawide.
High Risk of Rip Currents on East coast through Monday, with High
Risk Sunday for Gulf Coast. Will be also monitoring for minor
tidal inundation along the Gulf coast Sunday, particularly around
high tide with is roughly midday. A Coastal Flood Statement is in
effect along the Gulf coast where a foot or so of inundation is
possible. Last but not least, Tropical Storm Warning in effect for
outer Gulf Waters, beyond 20 nm offshore. Latest observations from
buoys in the Gulf and also in and near the Keys should tropical
storm force wind gusts are likely already occurring in this area.
8PM NHC advisory on Subtropical Storm Alberto reveals weak,
disorganized storm with max. sustained winds of 40 mph, though
highest winds are present well east of the center. Alberto should
make its closest approach to South Florida during the morning
Sunday.