Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Tampa Bay Ruskin Florida
236 PM EDT Thursday Jul 31 2014
Short term (tonight - friday)...
a remnant frontal boundary from near Naples extending northeast
to near Melbourne this afternoon combined with the sea breeze
boundaries and deep layered moisture (pw's at or above 2 inches) along
and to the southeast of the frontal boundary will support scattered
shower and thunderstorm development from southeast Polk County
southwest to The Fort Myers area the remainder of the afternoon
with the convection lingering into the evening hours. A weak
steering flow will favor slow moving storms with some locally heavy
rainfall amounts possible. In addition to the rain some strong
gusty winds and frequent lightning will accompany the storms.
Weakening boundary interactions combined with loss of daytime
heating should allow the convection to gradually wind down by middle
to late evening tonight...with convective debris clouds thinning
with skies becoming partly cloudy overnight. May see some shallow
patchy fog develop (especially in areas which receive rain) early
Friday morning...but think overall coverage will remain too low to
mention in the grids/zones at this time. It will become
increasingly humid overnight as deeper moisture works it way back
into the area from the southeast with rising dew point values
expected...with overnight lows ranging from the upper 60s over
the Nature Coast to the lower to middle 70s central/southern interior
zones...and upper 70s to near 80 along the immediate coast.
On Friday deeper moisture (pw's increasing back toward 2 inches)
will continue to spread into the forecast area from the southeast
as the aforementioned frontal trough drifts northwest and becomes
diffused as high pressure surface and aloft over the western
Atlantic noses in across the south-Central Peninsula. The increasing
moisture coupled with the developing east and West Coast sea breeze
boundaries should yield higher rain chances across the entire
forecast area with scattered showers and storms expected to develop
and increase in areal coverage from middle morning on with highest probability of precipitation
likely to set up along the I-75 corridor along the sea breeze merger
during the afternoon and early evening hours. The deep moisture
combined with a very weak southeast steering flow (via model
sounding data) will again support slow moving storms with the
potential for some very heavy rainfall amounts in some locations.
Temperatures on Friday will be within a degree or two of seasonal
norms with highs climbing into the upper 80s to around 90 along the
coast...and lower to middle 90s inland.
Middle term (friday night - saturday)...
longwave pattern will remain unchanged with a dominant western
ridge and a persistent (some might say stubborn) eastern Continental U.S.
Trough. Generally speaking any measurable synoptic influence for
lift associated with this trough...along with the main associated
belt of westerlies aloft will remain to our north and northwest
through the period. While the remainder of the eastern Continental U.S. Is
under this trough...the Florida Peninsula will see more influence
from an upper ridge the extends from the western
Atlantic...southwest over the peninsula into the southeast Gulf of
At the surface...Main Ridge axis will be well to our northeast over
the western Atlantic...with an inverted trough axis/surface
reflection associated with the troughing aloft extending from the
northern Gulf Coast to the Carolina coast. This fairly complex
pattern should result in a southeast/east-southeast low level synoptic flow across the
majority of the peninsula. This southeast flow will become more
defined over time and likely help set up an active period of diurnal
thunderstorms...especially on Saturday when the flow will be
strongest. Synoptic flow with an easterly component is the favored
flow for enhanced sea-breeze convergence and convective coverage
along the Florida West-Coast with a bias toward late day/evening
storms. That being said...Saturday does not look like an overly wet
day...as we will likely see fair weather for much of the day in any
one location...however those planning outdoor activities for the
second half of the day should have thunderstorm contingency plans as
well. This is kind of true for most days in the Summer around these
parts...but with the easterly flow...the late day coverage of storms
has a better chance of being numerous in nature.
Temperatures are looking seasonable with mainly lower 90s for highs and 70s
for lows. May see a few upper 60s for portions of the Nature Coast
early Friday morning...but increasing moisture by the weekend should
prevent any stations from dropping below 70 Saturday morning.
Long term (sunday - thursday)...
synoptic pattern portrayed by both the GFS and European model (ecmwf) for the
second half of the weekend becomes more messy and ill-defined.
Upper trough over the eastern Continental U.S. Tends to dip a bit further
south over the north- central Gulf of Mexico. The result of this
is two-fold. First...the upper ridge retreats back to the east a
bit and leaves our region in a weakly defined zone to the east of
the main trough axis...and also the GFS/European model (ecmwf) both shows some weak
surface troughing developing over the eastern Gulf of Mexico. This
weak surface trough makes the pressure pattern messy at the
surface and make predicting the dominant low level flow direction
much more difficult. One this is clear on both the GFS/ECMWF...and
that is that there really is not any negative factors for high
coverage of thunderstorms on Sunday. Plenty of column moisture in
place...and little to no upper level suppression. Will show higher
than climatology rain chances...especially in the afternoon and slightly
cooler temperatures in anticipation of more cloud cover.
Good agreement between the GFS/European model (ecmwf) that the upper ridge will then
build back overhead during the middle portion of next week...and
strengthen. After another active convection day on Monday with above
climatology rain chances...Tuesday looks to be the transition day as the
influence of the upper trough on our weaker begins to dissipate.
Weak little tropical impulse currently over the central Atlantic is
shown by both guidance members to slip in under the building ridge
toward the Bahamas by later Monday or Tuesday...but at this point
looks to have little to no impact on our region as the upper flow
then forces the energy north and then northeastward away from the
Continental U.S.. the bigger story by the middle and later portion of next
week (assuming the pattern forecast by the GFS/European model (ecmwf) verifies) is
that a strong ridge centered over the peninsula would suggest some
hot temperatures...and the suppressive factors and warm temperatures aloft
would be rather hostile toward deep convection. Will show temperatures a
bit warmer than guidance by Wednesday and rain chances lower than
guidance as climatology will be playing a significant influence on these
MOS numbers this far into the forecast period.
developing rain showers/thunderstorms and rain may bring brief MVFR/IFR conditions to kpgd
kfmy and krsw terminals through 01z tonight and have handled with
thunderstorms in the vicinity for now with possible short tempo groups becoming necessary
in any amendments. Other than this VFR is expected. West to
northwest winds in the 6 to 8 knot range this afternoon with gusts
up to 40 knots possible in the vicinity of thunderstorms and rain will become variable
at or below 5 knots after 01z tonight.
a frontal trough across the south Central Peninsula this afternoon
will lift northwest and become diffused tonight and Friday as high
pressure surface and aloft over the western Atlantic builds west
across the south Central Peninsula. A weak pressure pattern under
the high will support tranquil boating conditions with light winds
and seas over the coastal waters tonight through the early next
week with wind directions and speed being dictated by sea/land
breeze circulations each day and night. Increasing moisture will
lead to increasing chances for showers and storms on Friday and
continuing through the weekend and into early next week with higher
winds and seas the primary concern.
increasing moisture and rain chances will keep humidity values
well above critical levels Friday and into the upcoming weekend
with no red flag conditions expected. Weak 20 foot winds and
transport winds will support dispersions in the poor to fair
range tonight through Saturday.
Preliminary point temps/pops...
tpa 76 91 77 92 / 10 40 30 60
fmy 75 93 77 94 / 20 50 30 70
gif 75 93 75 93 / 20 50 40 50
srq 74 91 76 92 / 10 40 30 60
bkv 68 92 72 92 / 10 40 30 60
spg 80 90 80 91 / 10 40 30 60
Short term/aviation/fire weather...57/McMichael
middle term/long term...14/mroczka