Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Tampa Bay Ruskin Florida
342 am EDT Friday Aug 28 2015
Synopsis...in the middle/upper levels...the long wave trough over the
East Coast is beginning to weaken which will allow for the
subtropical high pressure ridge to shift more northward and build
west over the Florida Peninsula. As the flow to the north becomes
more zonal...the remnants of the deep troughing results in a closed
middle/upper level low off the northern Gulf Coast. The stationary
frontal boundary extending along the eastern Seaboard will lift
northeast and dissipate over the next day as the subtropical ridge
moves northward and strengthens.
Short term (today-saturday)...as the subtropical ridge moves
northward...a more seasonal pattern will setup over the Florida
Peninsula which will shift the winds from the southwest to a more
east southeast direction. Latest water vapor imagery continues to
show abundant moisture...which combined with diurnal heating will
allow for scattered to numerous showers and storms to develop on
Friday and Saturday. Some showers and storms have begun firing up
over the coastal waters in the past couple of hours. Those storms
will make their way toward the coastline later this morning. This
will continue through the morning hours and then showers/storms will
progress over the inland areas late morning and afternoon. The
highest rain chances will once again occur with sea breeze
collisions between the West Coast sea breeze and East Coast sea
breeze over the inland counties. On Saturday...east southeast winds
will prevail which will favor the more typical east/West Coast sea
breeze convergence. Scattered to numerous storms can once again be
expected. Temperatures will be close to the seasonal norm with highs
near 90 and lows in the middle 70s.
Tropical Storm Erika currently located just to the south of Puerto
Rico is tracking west around 17 miles per hour. Models have the storm
continuing to track west northwest toward the Bahamas and along the
East Coast of Florida over the next 5 days. No direct impacts are
expected at the current time for central and southwest Florida but
we will continue to closely monitor this storm throughout the week
and into the weekend.
Middle/long term (saturday night-thursday)...
overall confidence not that high at this time as the forecast for
this period all depends on the eventual track and strength of Erika.
00z global models have come in further west again with the GFS and
European model (ecmwf) bringing a rather weak system northward off the West Coast of
Florida...while the Canadian continues to show a pretty strong
system now moving up over the peninsula. The official NHC forecast
is still up along the East Coast of Florida at this time...but no
matter which way the system moves it does look like we will see an
increase in rain chances for the first few days of the middle/long term
period. For now have used a consensus of the models and gone with a
50 to 70 percent chance of showers and storms Sunday...Monday and
Tuesday...then back to 40 to 50 percent for Wednesday and Thursday
as the system should be north of the area with a return to more
typical afternoon and evening convection.
Daytime high temperatures should be near to a few degrees below
normal in the middle to upper 80s for Sunday through Tuesday thanks to
the expected increase in clouds and moisture...then near normal for
Wednesday and Thursday with highs back into the the upper 80s to
lower 90s. Overnight lows will remain near normal in the middle 70s
inland to near 80 along the coast through the period.
Aviation...overall VFR conditions will prevail through the period.
Scattered showers and isolated thunderstorms can be expected so will
keep thunderstorms in the vicinity at all terminals starting at 12z. Brief MVFR/IFR ceiling
and visibility conditions are possible in the vicinity of heavier
rains and thunderstorms.
Marine...subtropical high pressure shifts north which will cause a
shift in the winds from southwest to a more typical east southeast
direction. Winds will remain below 10 knots and seas 2 feet or less
through Saturday except in the vicinity of thunderstorms where
locally heavy rain...gusty winds...locally higher seas...and
frequent cloud to water lightning will occur. Conditions will
deteriorate on Sunday and into next week as Tropical Storm Erika
approaches the area. Winds and seas approaching small craft criteria
can be expected starting on Monday through middle week.
Fire weather...no fire weather issues are anticipated as a moist
tropical air mass remains over the Florida Peninsula.
Preliminary point temps/pops...
tpa 90 77 90 77 / 40 30 50 30
fmy 91 75 92 76 / 50 10 60 30
gif 92 75 91 75 / 60 30 60 30
srq 89 75 90 76 / 50 20 40 30
bkv 91 73 90 73 / 50 40 50 30
spg 90 78 90 78 / 40 20 40 30
Synopsis/short term/aviation/marine/fire weather...74/Wynn
middle/long term/decision support...69/close