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fxus62 ktbw 221158 

Area forecast discussion
National Weather Service Tampa Bay Ruskin Florida
758 am EDT Sat Jul 22 2017

showers and thunderstorms this morning near the coast will
expand inland through the afternoon. Have a tempo at ksrq
where there is currently a thunderstorm in place, and thunderstorms in the vicinity
elsewhere for nearby storms. Activity should subside after
01z, with light and variable winds overnight.


Prev discussion... /issued 313 am EDT Sat Jul 22 2017/

07z water vapor and h4 rap analysis show the Florida Peninsula under
a region of weak flow aloft. In the mid-levels our region resides
between an area of upper ridging over the Atlantic...and a weak
upper low retrograding westward across north-central Gulf
of Mexico. While the low to our west has vertical extent
into the upper troposphere, the upper ridge to our east does
not. Above the 500 mb level, this ridge quickly breaks down and
transitions to a TUTT cell migrating westward over the
Bahamas. All-in-all the upper levels are rather complex over
our vicinity of the world, yet no feature is really going
to have a significant impact on our weather today.

The main belt of northern stream westerlies are displaced well to
our north (where they should be this time of year), and any synoptic
features of lift associated with it, will also stay well away from
our region.

At the surface, the subtropical ridge axis remains aligned over the
south-central Florida Peninsula, providing our region with a light
1000-700mb SW flow pattern, that will persist for the extent of the
weekend. This deeper low level SW flow pattern is climatologically
favorable for late night/early morning convective activity forming
along the land-breeze over the coastal waters...and then
tending to migrate onshore. We have seen this the past
couple of mornings, and today will be no different. Activity
will not be widespread, but those out early this morning
near the coast can expect to Dodge a brief shower or two,
perhaps a few rumbles of thunder. This flow pattern, because
winds are weak but also tend to push convective cells to
the coast, is also favorable for the development of isolated
brief and generally weak 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. Keep in mind, it does not take
strong convection to produce these morning waterspout
events. Even a weak updraft encountering a favorable
thermodynamic and vorticity profile can spin up a brief visible

Short term (today through sunday)...
today...light southwest flow dictates the main weather features
through the day. Southwest flow is highly favorable for the
development of shallow coastal showers/storms during the pre-dawn
hours, which then migrate onshore during the morning hours.
Generally speaking these showers do not survive far inland within a
few hours of sunrise, as they migrate away from their source of
focus and instability. Therefore, highest rainfall chances through
15z will remain near the coast. Thereafter, diurnal
insolation and resulting instability further inland supports
increasing convective potential along outflow/sea-breeze
boundaries migrating inland with the synoptic flow. Will
increase rain chances over inland areas during the afternoon
to coincide with climatology under light SW flow. Generally
speaking, by late in the afternoon, rain chances should have
significantly fallen off close to the coast...and this will
be in the forecast. However, the light flow can
occasionally fail to prevent outflow from inland storms to
migrate back westward, providing focus for another round of
storms back toward the coast in the evening. This scenario
is very difficult to accurately predict far in advance...and
is not part of the current forecast. Scattered storms will
become more isolated with time after sunset and generally
end over the land zones by midnight. Temperatures will end
up within a couple degrees of 90 for most locations, close
to where high temps should be in late July.

Sunday...after midnight the continued southwest flow will favor
re-development of scattered shallow convective activity
over the coastal waters. There are some indications that the
low level pressure gradient during the pre-dawn hours will
favor slightly better low level convergence/focus off the
Nature Coast compared to previous mornings, and a resulting
higher coverage of showers developing and migrating toward
shore from Pinellas County northward through the morning
hours. Will have highest rain chances Sunday morning over
the northern coastal waters and adjacent land zones, and
then similar to today, decrease activity near the coast
during the second half of the afternoon, while increase rain
chances inland from the I-75 corridor.

Long term (sunday night - friday)...
very little change in the overall pattern is forecast for the first
half of next week, with the sub-tropical surface ridge continuing to
extend from the Atlantic into the southern half of the Florida
Peninsula. This will keep weak winds in place, although the low
level flow will generally be a bit more westerly/southwesterly north
of Interstate 4 along the northern side of the ridge. With abundant
moisture available, the pattern will continue to feature scattered
early morning thunderstorms developing over the Gulf and shifting
east into the Florida Peninsula through the morning and early
afternoon. Storm coverage will become more numerous each afternoon
under strong surface heating, before storms dissipate and shift into
the interior through the early evening hours.

During the second half of next week, a mid level trough will build
into the eastern Seaboard, shifting the surface ridge to the
southeast. This will bring a slight increase in the westerly low
level flow, but the increase will not be enough to drastically alter
the pattern of morning convection over the Gulf shifting east into
the interior throughout the day. Scattered to numerous storms will
still be expected each afternoon, with the highest coverage
generally expected over the interior. Temperatures will remain
seasonable, with highs around 90, and morning lows in the mid to
upper 70s.

Aviation (22/07z through 23/06z)...
general VFR conditions can be expected through the morning
hours. However, southwest flow will promote a scattering of
showers/storms migrating onshore from the Gulf. Any terminal
may see a brief cig/vis restriction with the passage of one
of these showers. The majority of the showers/storms should
migrate inland from the terminals during the later
afternoon/evening hours, with the exception of klal. Winds
outside of any storms generally remain less than 10 knots
through the taf period.

surface ridge axis remain in a position over the southern half of
the Florida Peninsula into the eastern Gulf of Mexico through the
next several days, 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.

Fire weather...
no significant fire weather concerns expected as a moist Summer
pattern remain in place through the next several days. Winds will
generally be light from the south or southwest, 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 significant or widespread fog or visibility
restrictions are expected through the next several days.


Preliminary point temps/pops...
tpa 89 78 88 79 / 50 30 50 20
fmy 90 76 90 77 / 40 20 40 20
gif 91 75 90 75 / 50 30 50 20
srq 87 78 87 77 / 50 30 50 20
bkv 89 74 88 74 / 50 30 50 20
spg 89 78 88 79 / 50 30 50 20


Tbw watches/warnings/advisories...
Gulf waters...none.

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