Area Forecast Discussion
Issued by NWS Tampa Bay Area, FL
FXUS62 KTBW 251928
Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
328 PM EDT WED MAY 25 2016
.SYNOPSIS (Current through this evening)...
19Z water vapor and H4 RAP analysis shows broad general troughing
still in place over the Florida Peninsula. However...this trough
is beginning to shift eastward as upper ridging from the
western/central Gulf of Mexico continues to build over-top into
the southeastern Conus. This evening through Thursday morning...
this progression will leave our region within a weakness in the
upper pattern between the ridge to our west/NW...and
troughing/lowered heights to our east. For the very short term we
are still located underneath the very backside of this
trough...with a weak shortwave...still seen clearly in WV
imagery...dropping south of our region toward the Fl Keys. As the
trough has begun to shift eastward...this has allowed our
mid/upper winds to veer from west/NW to a more northerly direction
as sampled by the 12Z KTBW RAOB. The sounding from this morning
was still on the dry side for late May with a PW value just over
1"...however it is not nearly as dry as it was yesterday morning.
At the surface...1025mb high pressure centered off the SE CONUS
coast continues to ridge back to the west and southwest across the
northern FL peninsula and NE Gulf of Mexico. The gradient around
this ridge is providing a general easterly wind flow through our
forecast area. VAD wind profile from KTBW radar confirms the
signal from earlier NWP runs showing a healthy easterly flow of
15kts above the surface (mainly above 1kft). These speeds are
borderline to be able to significantly disrupt the sea- breeze
formation. Later in the year when the ocean/land temp gradient is
less...the sea- breeze would likely fail to form or stay
completely offshore under this setup. However...given the early
time of year when the sea-breeze tends to be stronger...and more
resilient. 19Z observations show the winds has flipped light
onshore at a few coastal locations...but these winds just above
the surface opposing the sea-breeze will likely keep it pinned at
the coast for the remainder of the day.
With the general troughing pulling to the east...the shortwave
dropping south of our area...we are left with little to no
synoptic forcing for ascent over our region late this afternoon.
Combine this with a still climatological dry trop column and lack
of inland sea-breeze penetration...and there really very little to
focus deep convection. The "best" chance for a few isolated
showers very late afternoon/early evening will be along the
immediate coast from Pinellas county south to Sarasota and Lee
counties...where the sea-breeze focus will be maximized. Would
expect the same maximized focus along the immediate Nature
coast...but should simply be too dry in order to support a
convective column. It still may very well end up being too dry
even along the suncoast...but will leave a narrow strip of 20%
PoPs along the immediate coast starting 20-21Z...since a few
generally reliable hires convection allowing models (HRRR/NSSL
WRFARW/NCEP HIRESARW) continue to supporting isolated activity.
However, as mentioned in the morning AFD...These models tend to
generally be too aggressive with storms...so the fact that even
they are sparse with coverage...suggests very isolated convective
cells at best over the next several hours. The shallow nature of
any showers and the defined flow above the surface suggests
anything that does develop will quickly push offshore over the
coastal waters this evening. Have kept a 20% chance for isolated
showers/storms across the coastal waters adjacent and south of
Pinellas county through 03-05Z.
.SHORT TERM (Overnight through Thursday)...
Any lingering isolated showers along the suncoast are quickly
pushed offshore setting the stage for a dry overnight period with
a light but steady easterly flow. Comfortable low temperatures
across much of the interior where overnight temps fall into the
middle 60s at most locations (even a few lower 60s for normally
cooler spots across the Nature Coast). With the easterly
flow...normally warmer locations with water influence...such as
southern Pinellas County and eastern Charlotte/Lee counties will
hold in the lower to middle 70s.
Thursday...GFS/ECMWF are in good agreement showing a swath of
renewed large scale suppression and drying arriving over the
region by morning in the mid/upper levels. Closer to the
surface...the pattern will be very similar to today...with
elevated easterly flow pinning the sea-breeze to the immediate
coast or holding the boundary just offshore. Both of these factors
suggest a rain-free day forecast area-wide. Current forecast grids
shows rain chances at 10% or less for the entire area...and based
on latest guidance...agree with this optimistic forecast. High
temperatures thursday afternoon reaching up into the upper 80s for
most spots with warmer locations briefly touching 90.
Have a great evening everyone!
.Mid/Long Term (Thursday Night-Wednesday)...
The models are in reasonable agreement with placement of the
upper low which will remain off the east coast Friday then start
to drift north Saturday. On the surface is an inverted trof east
of the Bahamas that becomes a weak closed low that drifts to the
northwest.The models vary on development of the system that
lingers off the coast near Jacksonville. The cold core low will
increase instability and chances for showers and thunderstorms
primarily over interior areas into the weekend and early next
week. By Monday the upper low center is near the coast of South
Carolina producing a northwest flow aloft for the forecast area
and the models vary on development of the surface system that
lingers off the coast near Jacksonville. By Tuesday the center of
the upper low has weakened and moved to coastal North Carolina
with the shortwave trough just off the east coast and weak ridging
extends over south Florida. Temperatures initially in the 60s at
night will warm during the period into the 70s with highs in the
upper 80s to near 90 through the period.
25/18Z-26/18Z. VFR SCT cumulus with bases above 4kft...LCL BKN.
ISOLD SHRA late afternoon/early evening near the immediate coast
but little if any impact at the terminals. Winds slacken and
become less gusty withing a few hours of sunset...remaining east
or ne through TAF period.
HIGH PRESSURE REMAINS ALIGNED ACROSS THE NORTHEAST GULF OF MEXICO
THROUGH THE NEXT COUPLE OF DAYS. THIS POSITION WILL KEEP A GENERAL
EASTERLY FLOW PATTERN IN PLACE OVER THE EASTERN GULF WITH
NOCTURNAL STRONGER SURGES OF WIND (PERHAPS TO CAUTIONARY LEVELS)
DURING THE OVERNIGHT AND EARLY MORNING HOURS. WILL BE KEEPING AN
EYE ON A POTENTIAL TROPICAL DISTURBANCE TO THE EAST OF FLORIDA
THROUGH THE EARLY PORTION OF THE UPCOMING WEEKEND...HOWEVER
CURRENTLY THIS SYSTEM DOES NOT APPEAR TO HAVE MUCH IMPACT ON OUR
LOCAL WINDS AND SEAS THROUGH SATURDAY.
HIGH PRESSURE WILL REMAIN IN PLACE ACROSS THE NORTHERN FLORIDA
PENINSULA THROUGH FRIDAY. RELATIVE HUMIDITY VALUES WILL APPROACH
35 PERCENT FOR A COUPLE OF HOURS THURSDAY AFTERNOON...HOWEVER
WINDS ARE GENERALLY EXPECTED TO REMAIN BELOW CRITICAL LEVELS.
ALTHOUGH CRITICAL LEVEL WINDS ARE UNLIKELY AT THE SURFACE...
STRONGER WINDS ALOFT AND EFFICIENT MIXING RESULT IN HIGH
DISPERSION INDICES THURSDAY AFTERNOON. THE LARGE SCALE SETUP WILL
BE SIMILAR FOR FRIDAY...ALTHOUGH LOW LEVEL MOISTURE STARTS
TO INCREASE AND LIKELY PREVENT ANY CRITICAL LEVELS OF RELATIVE
HUMIDITY FROM BEING REACHED. THERE WILL ALSO BE A BETTER
POTENTIAL FOR A FEW SHOWERS...MAINLY ALONG AND SOUTH OF THE I-4
CORRIDOR DURING THE LATE AFTERNOON OR EARLY EVENING.
FOG POTENTIAL...NO SIGNIFICANT FOG IS EXPECTED THROUGH THE NEXT
.Preliminary Point Temps/PoPs...
TPA 70 89 70 88 / 10 0 0 10
FMY 69 88 67 89 / 0 10 0 20
GIF 66 87 67 87 / 0 10 0 20
SRQ 69 86 68 87 / 10 0 0 10
BKV 63 88 62 88 / 0 0 0 10
SPG 72 88 72 87 / 10 0 0 10
SYNOPSIS/SHORT TERM/AVIATION/MARINE/FIRE WX...Mroczka
MID TERM/LONG TERM/DECISION SUPPORT...Paxton