Area Forecast Discussion
Issued by NWS Tampa Bay Area, FL

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FXUS62 KTBW 270906
AFDTBW

Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
506 AM EDT WED JUL 27 2016

.SYNOPSIS...
08z water vapor and H4 RAP analysis shows a zonal pattern in the
northern stream across the northern tier of the country...and
running off the NE/Mid Atlantic Coast. To the south of this zonal
flow we find a large mid/upper level ridge in place over the SE
Conus and off into the western Atlantic. The Florida Peninsula
resides on the southwest periphery of the circulation of this ridge
and to the NE of an upper level low migrating slowly westward across
the Gulf of Mexico. At this point...it is clear the the upper ridge
has more control over our weather...and its influence will only
increase further during the next 12-24 hours. As the ridge builds
more and more over our region...so will the synoptic
suppression...and advection of drier air swaths over the state from
the east and southeast.

At the surface...The subtropical ridge axis is aligned from just
north of the Bahamas...into the north-central FL peninsula...and
then over the NE Gulf of Mexico. This position provides a synoptic
southeasterly flow in the lower levels to the south of the I-4
corridor...and a more light/variable flow pattern for the Nature
Coast.

Radar is showing some showers and storms off the coast this
morning in a typical land-breeze configuration. As opposed to
Tuesday morning...the land breeze is more defined today...and is
keeping the storms from migrating back toward the coast. In
fact...the progress is actually further offshore with time this
morning. Therefore...mariners headed out on the Gulf early this
morning will need to be prepared for a storm...but the convection
should generally not bother us on the coast.

&&

.SHORT TERM (Today through Thursday)...
The forecast through Thursday will increasingly be influenced by
the strong upper ridging building over the Florida peninsula.
There will be some increasing dry air overspreading our region
today...and this will likely somewhat limit the overall coverage
of storms during the afternoon/evening hours. While rain chances
will be running 40-50% over much of the region late today...these
numbers are actually 20% or so below normal for southeast low
level flow (especially south of Tampa Bay toward the Fort Myers
Area). Therefore...not going to be able to let our guard down with
respect to storms today...but coverage at any one time is likely
to resemble Tuesday...with storms in a more widely scattered
configuration...and struggling to persist as updrafts fight the
ingesting of drier/lower theta-e mid level air. One thing that we
can likely say, is that convection will get a late start. Very
likely we will not see much around west-central Florida until
after 20Z...and perhaps later than that for the Tampa Bay area.

Temperatures will be a bit above average today (especially inland) with
the building upper ridge. Look for high temperatures within a
degree or two of 90 at the beaches...and lower to middle 90s
inland.

The late start to the convection today...will allow what storms we
do have to persist for a while into the evening to the north of
the Sarasota area. Have kept a 30% chance PoP in the forecast for
the Tampa Bay Area and up into much of the Nature coast through
03Z...and would not be surprised to see a few storms going even
later than that. Eventually...all land storms will dissipate and
we will get a few late night storms over the Gulf. Although the
upper ridge and drier air will really be building over the region
by late tonight...land breeze storms are generally a shallower
type of convection...and not influenced as much by this type of
pattern aloft.

The land based sea-breeze storms on the other hand are likely to
be highly influenced by the upper ridge during the
afternoon/evening hours of Thursday. Once again the convection
will likely get a very late start...and forecasting well below
climatology rain chances for the synoptic low level pattern.
Updrafts will certainly struggle with the hostile environment
aloft. This looks to be especially true from the Tampa Bay/I-4
corridor and northward...where most reliable NWP guidance members
show a deep unseasonably dry airmass lingering through the
diurnal cycle. Have only gone with a 20% chance/isolated storms
for these zones. The dry air may not be quite as hostile around
the fort myers area by late in the day...and have gone with
30%/widely sct storms for Charlotte/Lee Counties. However...as we
discussed above...this is significantly below average (30+%
below) for a southeast low level flow pattern.

Very warm afternoon on tap Thursday with the upper ridge firmly
in control and not many rain cooled areas. Look for high temps
around 90 at the beaches and widespread middle 90s inland.
Although temperatures will be above average...not really
anticipating heat indices to be much above average. The boundary
layer will become well mixed by the time of peak heating and bring
down some of the drier air from aloft. This will not only further
decrease the instability and ability for strong convective
updrafts...but will lower dewpoints a few degrees and keep heat
indices in check.

Have a great Wednesday everyone!

&&

.Mid/Long Term (Thursday Night-Tuesday)...
A strong U/L ridge will be centered over Florida Friday. An U/L
trough digging over the the Great Lakes and mid Mississippi Valley
over the weekend will cause the center of the U/L ridge to shift
east over the central Atlantic, however the ridge axis will extend
west across the Florida peninsula. A TUTT cell will likely move
across the Florida straits over the weekend with drier cooler air
aloft advecting over the forecast area associated with the north
side of the TUTT. This may increase the threat for a few strong
storms Saturday and Sunday afternoon with the main threat damaging
wind gusts. The TUTT should move west over the central Gulf of
Mexico on Monday however the trough axis may remain across the
Florida peninsula which could enhance afternoon thunderstorm
activity across the forecast area.

Surface high pressure will remain anchored over the central Atlantic
with the ridge axis extending across the central Florida peninsula
through the period.  Generally east to southeast boundary layer flow
will occur across the forecast area each day which will hold the
west coast sea breeze boundary over the coastal counties. The ridge
axis may sink a bit south on Saturday with onshore southwest flow
developing over the nature coast.  The ridge axis should shift a bit
back to the north on Sunday into early next week.  Scattered showers
and thunderstorms will develop across the forecast area each
afternoon and will be enhanced along the west coast sea breeze
boundary late in the afternoon/evening each day. Temperatures will
continue to run above climatic normals through the period with high
temperatures in the lower to middle 90s each day.

&&

.Aviation (27/09Z through 28/06Z) VFR conditions prevail across
west- central Florida early this morning. VFR conditions prevail
into the early afternoon hours. A scattering of typical summer
storms can be expected...mainly after 19Z. Storms come to an end
within a few hours of sunset...with prevailing VFR conditions at
all terminals into Thursday morning.

&&

.MARINE...
High pressure will remain over the eastern Gulf of Mexico through
the remainder of the week. The proximity of the ridge axis will keep
winds and seas generally low through the period. Mariners can expect
scattered typical early morning showers and storms...and another
possible round of storms late in the afternoon or early evening each
day. Conditions will be locally rough in the vicinity of any
thunderstorms.

&&

.FIRE WEATHER...
No significant fire weather concerns anticipated through the
remainder of the week. High pressure will remain in control of the
region...with temperatures generally running slightly above average
and coverage of afternoon and evening thunderstorms running a bit
below average. Despite the hot daytime temperatures...relative
humidity values are still anticipated to remain above critical
values through the period.

&&

.Preliminary Point Temps/PoPs...
TPA  92  77  92  80 /  50  30  20  20
FMY  93  76  92  78 /  40  10  30  20
GIF  95  76  95  77 /  30  20  20  10
SRQ  89  78  92  78 /  40  20  20  20
BKV  94  75  94  74 /  50  30  20  10
SPG  91  79  92  80 /  50  30  20  20

&&

.TBW Watches/Warnings/Advisories...
FL...None.
Gulf waters...None.

&&

$$

SYNOPSIS/SHORT TERM/AVIATION/MARINE/FIRE WX...Mroczka
MID TERM/LONG TERM/DECISION SUPPORT...Oglesby



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