Area Forecast Discussion
Issued by NWS Tampa Bay Area, FL
FXUS62 KTBW 270032
Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
832 PM EDT MON SEP 26 2016
.UPDATE (Rest of Tonight through Tuesday)...
Another active day of convection across west-central and
southwest Florida is slowly coming to an end. Healthy storms
continue up over Levy county...but elsewhere the convection is
decaying or has moved offshore into the Gulf of Mexico.
Why was the convection stronger today than usual...with a few
severe storms and lots of reports of hail? Well...the answer to
that question can be seen on water vapor imagery and in the column
sampling from the 00Z KTBW RAOB from this evening. 00Z water vapor
and H4 RAP analysis shows troughing/closed low spinning over the
Florida Peninsula. Upper lows are cold core and often contain a
pocket of cooler than normal air in the mid/upper levels. This
upper low is no exception. The evening sounding showed 500MB temps
at or just below -10C...with zones of very healthy lapse rates
and decent CAPE through the hail growth zone. This -10C reading at
500mb is cold for this time of year...and helped support some very
strong updrafts and efficient hail production aloft.
Storms still around will slowly diminish into the later evening
hours...and after 11 PM or so...expect much of the area to see a
dry overnight period. These dry conditions will linger through the
morning hours Tuesday. The trough and some of the cold influence
aloft will still be around for Tuesday afternoon...although it
will be starting to shift eastward. The big difference from a
synoptic point of view between Monday and Tuesday...is that
Tuesday will see a much more defined low level 1000-700mb
southwesterly wind flow develop. This wind flow will help to more
rapidly propel the sea-breeze inland through the afternoon
hours...and help prevent convective outflow from heading back
west. Therefore...A few storms are possible near the beaches early
in the afternoon as the sea-breeze initially develops...but then
better chances will quickly shift inland past the I-75 corridor by
the later afternoon and evening hours. As I mentioned
above...these more easterly inland zones will also be under the
coolest temps aloft by later Tuesday. With this in mind...would
expect to see a good potential for strong updrafts...and resulting
small hail and intense lightning producing storms across portions
of Polk/Highlands/DeSoto/Hardee Counties. Obviously...weather does
not follow political boundaries...so anywhere in that vicinity
will potentially see stronger storms tomorrow. Before the storms
start to develop...temperatures will rise to within a degree or
two either side of 90 for afternoon highs.
Thanks for reading and have a great rest of your Monday evening...
Convection is dissipating across west-central and SW Florida.
Small potential for a pop up storm near KFMY/KRSW through
02Z...but otherwise the storms are over. Cirrus canopy from
today`s storms will dissipate over next few hours...with VFR
conditions and light winds in place through the remainder of the
overnight. General VFR conditions expected for much of Tuesday as
well. Best potential for afternoon storms will be away from the
coast as a more defined southwesterly low level flow helps push
the sea-breeze well inland after mid-afternoon.
.Prev Discussion... /issued 306 PM EDT MON SEP 26 2016/
SHORT TERM (Tonight - Tuesday)...
Currently in the upper levels, broad low pressure is spinning over
the northeastern Gulf of Mexico and is forecast to drift south
towards the Tampa Bay through tonight. This low is bringing cooler
temperatures in aloft, which could help support a few stronger
storms this afternoon/evening and again on Tuesday. At the surface,
a ridge of high pressure is currently sitting off the Mid-Atlantic
coast, while a cold front pushes into the southeastern CONUS.
Meanwhile, the Florida Peninsula remains under rather weak flow,
with slow steering flow keeping storm motion nearly stationary. With
precipitable water values holding around 1.5 inches or more, expect
scattered thunderstorms to develop again on Tuesday across the area.
Overall, Tuesday will shape up much like what was seen this weekend
and again today, with a few storms lingering over the waters through
the early morning hours, then isolated storms developing over the
Florida Peninsula during the early afternoon and expanding to
scattered coverage through the late afternoon and early evening
hours. Storms will then shift offshore and mostly dissipate through
the evening and overnight hours.
Temperatures will remain near to a couple degrees above normal, with
highs from the upper 80s to around 90, and lows tonight in the
MID/LONG TERM (Tuesday Night-Monday)...
Models in good agreement through the work week then start to
diverge over the weekend and into next week. Latest solutions
continue to keep large closed upper low spinning from north of the
the Great Lakes region Tuesday Night sinking southward into the
Ohio River valley Thursday. This low and associated trough moving
over the Gulf Coast region to push a surface cold front through
the Deep South mid- week and over the C FL peninsula Thursday
before stalling Friday. Expect warm and humid conditions with
diurnal scattered to numerous storms over the area ahead of the
front and then convective activity to be confined and remain south
of the front to end the week and into the weekend. Exact southern
extend of the front still in doubt, but expect much drier and not
as warm conditions over the N FL Peninsula to end the week into
the weekend. Upper low to lift into New England late in the
weekend and Monday but its still uncertain what, if any,
troughiness will remain in the region to steer any possible
Weak high pressure will continue to hold north of the waters through
the next several days, with light and generally east winds turning
onshore each afternoon with the sea breeze. Scattered thunderstorms
will develop over the Florida Peninsula each afternoon and shift
west into the Gulf during the early evening, with a few storms
lingering overnight. Outside of thunderstorm activity, winds and
seas will remain rather light through the period.
Relative humidity is forecast to remain above critical thresholds
through the week, with no fire weather concerns expected.
.Preliminary Point Temps/PoPs...
TPA 75 88 76 87 / 20 30 10 40
FMY 74 89 75 88 / 50 40 20 40
GIF 72 90 73 88 / 20 50 10 50
SRQ 75 88 76 87 / 20 30 20 40
BKV 70 90 72 87 / 20 30 10 40
SPG 77 88 78 86 / 20 30 20 40
FL...Beach Hazards Statement through Thursday evening for
Coastal Manatee-Coastal Sarasota.