Area Forecast Discussion
Issued by NWS Tampa Bay Area, FL

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FXUS62 KTBW 230658

Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
258 AM EDT Sun Jul 23 2017

07Z water vapor and H4 RAP analysis shows a weak flow pattern but an
unsettled one aloft over the Florida peninsula this morning. The
subtropical surface ridge extends up to around the H7/700mb level
before transition to generalized troughing rising higher in
altitude. This troughing is on the western periphery of the
circulation around a well-defined TUTT low moving slowly northward
off the southeast CONUS coast. As this TUTT begins to move away from
the region later today, the extent of the unsettled troughing aloft
will begin to weaken, but likely not before diurnal heating has
already interacted with this energy to our convective
pattern/evolution for the day. Outside of our region, the main belt
of northern stream westerlies/migratory synoptic impulses remain
displaced well to our north, and will for the rest of the forecast

At the surface, the subtropical ridge axis remains aligned over the
south-central Florida peninsula, providing a continued light 1000-
700mb SW flow. This low level SW flow pattern is climatologically
favorable for late night/morning convective activity forming along
the land-breeze over the coastal waters and migrating onshore. We
have seen this the past several mornings, and today will be no
different...and potentially even more active from the Tampa Bay Area
northward along the Nature Coast due to a bit of enhanced low level
focus/convergence compared to previous days...superimposed
underneath some weak synoptic support/lift aloft. Several studies
conducted by this office have found that this light SW flow pattern
is also climatologically favorable for the development of isolated
brief and generally weaker waterspouts near the coast within a few
hours either side of sunrise, as cells migrate nearshore and
encounter old/residual boundaries to enhance updraft vorticity
stretching. Important to understand that it does not require strong
convection to produce these morning waterspout events. Even a weak
updraft encountering a favorable thermodynamic an vorticity profile
can spin up a brief visible funnel. Absolutely not saying that these
morning waterspouts are not potentially dangerous to mariners,
however the waterspouts we see later in the day when we are under
east/southeast flow tend to be stronger and longer lasting as they
are associated with more robust boundary collision updrafts.


.SHORT TERM (Today through Sunday)... Today...The pattern
today will be very similar to what we have seen the past
several days...driven mostly by the the light southwest flow
pattern off the Gulf of Mexico. Convective activity is
already going over parts of the Nature Coast as of 3AM, and
the pattern and NWP ensemble guidance both suggest this
activity will increase and spread south down the coast in
the remaining pre-dawn hours. The storms certainly have the
potential to be a bit more active/coverage during the
morning hours today due to more enhance low level focus in
the lower levels, and a weakness aloft that will help
promote rising motion. Unlikely many spots will be a washout
today, but anyone with outdoor activities/work planned
should be prepared to dodge a few showers/storms, especially
along and north of the I-4 corridor.

The later into the afternoon we progress, the more likely we will
see the best storm chances pushing inland. Based on the position of
the weakness aloft and the better potential for a migratory sea-
breeze along the suncoast, am expecting convection to become rather
quiet along the coast to the south of Tampa Bay after 18-20Z.
Further north, expect coverage to decrease, but will have to keep at
least a chance PoP in the forecast into the early evening hours.

Temperatures today will range from the middle 80s north under
greater  and rain coverage, to around 90 south of Tampa

Monday...The upper weakness will be lifting away from region during
Monday allowing height to rise overhead. We will still be under a
weak SW flow regime, so that patterns fingerprint of early morning
storms migrating in from the Gulf and slowly inland with time after
sunrise will still control the forecast. However, with less upper
level support, the overall coverage, duration, and  should
be less than today. With greater potential for insolation,
and greater heights, would anticipate high temperatures a
bit warmer than today. Most locations should reach 90, with
some southern areas down toward Punta Gorda/Fort Myers into
the lower/middle 90s.


.LONG TERM (Monday Night - Saturday)...
Monday night through Wednesday, the sub-tropical surface
ridge will hold across the southern half of the forecast
area, with weak westerly to southwesterly low level flow
holding in place across much of the area. This will continue
the pattern of scattered convection developing over the
eastern Gulf of Mexico before sunrise each morning, shifting
east into the Florida Peninsula through the morning and
early afternoon hours. Thunderstorms will become more
numerous each afternoon under strong surface heating and
will shift into the interior and dissipate through the
evening hours.

During the second half of the week, a mid level trough will move
into the eastern seaboard, allowing a weak surface front to stall
across the southeastern states, nudging the surface ridge to the
southeast. Although the low level flow will remain weak, generally
southwest flow will persist across the area between this stalled
front and the sub-tropical ridge. Storms will continue to develop
across the Gulf waters during the early morning hours and migrate
into West Central and Southwest Florida through the morning and
afternoon each day through the period.


.AVIATION (23/06Z through 24/06Z)...
Expecting general VFR conditions for this TAF period,
outside of occasional passing thunderstorms. Similar to
previous mornings, expect scattered storms to begin
migrating onshore during the pre- dawn hours and continue
after sunrise. A period of MVFR or IFR vis is possible with
any of these storms, with continues returning to VFR with
storm passage. The majority of the convective activity is
expected to migrate inland from the TAF sites by the later
afternoon and especially evening hours.


Surface ridge axis remain in a position over the southern half of
the Florida peninsula into the eastern Gulf of Mexico through
Monday, providing the region with a generally light southwest to
south wind. Winds and seas will generally be quite low, however
mariners should expect scattered thunderstorms, especially during
the overnight and morning hours.


No significant fire weather concerns expected as a moist summer
pattern remain in place through the next several days. Winds will
generally be light outside of thunderstorms, with relative humidity
well above critical values. Scattered storms can be expected near
the coast each morning...with activity spreading inland with time
through the day.

Fog Potential...No significant or widespread fog or visibility
restrictions are expected through the next several days.


.Preliminary Point Temps/PoPs...
TPA  87  78  90  79 /  60  30  40  20
FMY  90  76  93  77 /  30  20  10  20
GIF  89  75  93  76 /  50  20  40  20
SRQ  86  77  88  79 /  60  30  40  10
BKV  87  74  91  75 /  60  30  50  20
SPG  87  78  91  80 /  60  30  40  10


Gulf waters...None.



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