Area Forecast Discussion
Issued by NWS Tampa Bay Area, FL

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FXUS62 KTBW 170724
AFDTBW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAMPA BAY RUSKIN FL
324 AM EDT WED SEP 17 2014

...SOME LOCALLY HEAVY RAINFALL POSSIBLE TODAY...

.SYNOPSIS...
ALOFT - A RIDGE REACHED FROM THE WESTERN GULF COAST TO THE CANADIAN
ROCKIES WHILE A TROUGH EXTENDED FROM HUDSON BAY TO THE SOUTHEAST U.S.
AT THE SURFACE - HIGH PRESSURE WAS OVER THE CENTRAL U.S. ROCKIES
AND SOUTHERN HIGH PLAINS...A FRONTAL BOUNDARY ARCED FROM THE
CENTRAL PLAINS THROUGH THE GULF COASTAL AREAS TO LOW PRESSURE OFF
THE SOUTHEAST U.S. COAST...HIGH PRESSURE SPRAWLED ACROSS MUCH OF
THE NORTHEAST QUARTER OF THE CONUS...AND ATLANTIC HIGH PRESSURE
RIDGED ACROSS FL TO THE GULF.

&&

.SHORT TERM (TODAY - THURSDAY)...
THE UPPER RIDGE PIVOTS IT/S NORTHERN END OUT OVER THE CANADIAN
PRAIRIES WITH THE EASTERN TROUGH SHIFTING TO ALONG THE EASTERN
SEABOARD AND A SURFACE HIGH PRESSURE AREA MOVING OUT OF CENTRAL
CANADA TO THE GREAT LAKES REGION. AS THE RESULT THE LOW OFF THE
SOUTHEAST U.S. DEEPENS SOME AS IT TRACKS NORTHEASTWARD WITH THE
FRONTAL BOUNDARY SAGGING SOUTH...ACROSS CENTRAL FL TODAY THEN INTO
SOUTHERN FL TONIGHT WHERE IT LINGERS AND WEAKENS THU.

MODEL PWAT VALUES IN THE 2.0 TO 2.4 INCH RANGE WITH AND AHEAD OF
THE BOUNDARY ALONG WITH FRONTAL CONVERGENCE AND WEAK IMPULSES
ROTATING THROUGH THE BASE OF THE UPPER TROUGH AS IT MOVES EAST
WILL RESULT IN CONSIDERABLE CLOUDINESS AND HIGH RAIN CHANCES.
SCATTERED TO NUMEROUS SHOWERS AND ISOLATED TO SCATTERED
THUNDERSTORMS WILL TRAVERSE NORTHERN AND CENTRAL COUNTIES TODAY
THEN MOVE INTO SOUTHERN COUNTIES TONIGHT. THE SHOWERS AND STORMS
WILL HAVE THE POTENTIAL FOR SOME LOCALLY HEAVY RAINFALL
AMOUNTS...ESPECIALLY IN AREAS WHERE THE TRAINING OF SHOWERS AND
STORMS OCCUR. DURING THU SOME SLIGHT DRYING BEGINS TO WORK IN FROM
THE NORTH HOWEVER THERE WILL STILL BE ENOUGH MOISTURE AND
ENERGY...ESPECIALLY ACROSS THE SOUTH...FOR ISOLATED TO SCATTERED
COVERAGE. THE CLOUD COVER AND RAINFALL WILL HELP KEEP TEMPERATURES
NEAR NORMAL.

.LONG TERM (FRIDAY THROUGH NEXT TUESDAY)...
EXTENDED FORECAST PERIOD WILL BEGIN WITH LONGWAVE TROUGHING STILL
FIRMLY IN CONTROL ALONG THE EASTERN CONUS SEABOARD...EXTENDING DOWN
INTO THE NORTHEAST GULF OF MEXICO. BEGINNING TO LOOK MORE AND MORE
AS THOUGH FRIDAY MAY BE A SHOWERY / INCLEMENT DAY FOR AT LEAST A
PORTION OF THE FORECAST AREA. GLOBAL GUIDANCE COMING INTO DECENT
AGREEMENT AS TO THE SYNOPTIC PATTERN...BUT THERE ARE SOME
DIFFERENCES REGARDING HOW THAT SYNOPTIC PATTERN PLAYS OUT IN TERMS
OF SENSIBLE WEATHER. GFS/ECMWF/GEM ALL SHOWING A BROAD PIECE OF
SHORTWAVE ENERGY DIVING INTO THE BASE OF THE TROUGH OVER THE
NORTHEAST GULF OF MEXICO THURSDAY NIGHT AND THEN MOVING OVER THE FL
PENINSULA DURING THE DAY ON FRIDAY. LOOKING AT THIS SCENARIO FROM A
DYNAMIC/KINEMATIC PERSPECTIVE...AN UNSEASONABLY STRONG SWATH OF DEEP
LAYER Q-VECTOR CONVERGENCE EXPANDS AHEAD OF THIS ENERGY ACROSS THE
EASTERN GULF OF MEXICO AND INTO THE FLORIDA PENINSULA EARLY FRIDAY.
AT THE SAME TIME...UPPER LEVEL JET STREAK ENERGY ALONG THE HEIGHT
GRADIENT AHEAD OF THE TROUGH AXIS PUTS THE FL PENINSULA UNDER A
FAIRLY DIFFLUENT FLOW WITHIN ITS ENTRANCE REGION. THESE FACTORS SEEM
LIKE PRETTY DECENT SYNOPTIC INGREDIENTS FOR LIFT...ESPECIALLY WHEN
SUPERIMPOSED ON THE STILL VERY WARM WATERS OF THE GULF OF MEXICO.
KIND OF SURPRISED THAT WE ARE NOT SEEING MORE IN THE WAY OF QPF
WITHIN THE MODEL SUITE OVER THE FAR NE GULF/NATURE COAST ZONES. THE
GFS IS THE ONLY ONE THAT SEEMS TO BE PICKING UP ON THIS CONVECTIVE
POTENTIAL. FURTHER SOUTH...THE ENSEMBLE MEMBERS ARE MORE AGGRESSIVE
WITH KICKING OFF THERE CONVECTIVE SCHEMES.

SO WITH ALL THIS IN MIND...CONFIDENCE IN A WETTER FORECAST IS HIGHER
TO THE SOUTH OF THE I-4 CORRIDOR DURING LATE THURSDAY NIGHT AND INTO
FRIDAY. HOWEVER...FOR RAIN CHANCES...AM GOING ABOVE WHAT SEVERAL OF
THE MORE RELIABLE GUIDANCE MEMBERS WOULD SUGGEST FOR THE NORTHERN
HALF OF THE REGION. THINKING PERHAPS THE DEEPER MOISTURE TO THE
SOUTH IS TRIGGERING THE CONVECTIVE SCHEMES IN THESE MODELS ENOUGH AS
TO UNREALISTICALLY SUPPRESSING THE POTENTIAL FURTHER NORTH.
THEREFORE WILL GO LIKELY FOR RAIN CHANCES FOR THE TAMPA BAY AREA
SOUTHWARD...AND CHANCE POPS FURTHER NORTH. JUST CAN NOT SEE WHY THIS
SYNOPTIC PATTERN WOULD NOT SUPPORT AT LEAST SCT CONVECTION FOR OUR
NORTHERN ZONES AS WELL. WITH THE HIGHER RAIN CHANCES AND LIKELY
ABUNDANT CLOUD COVER ON FRIDAY...WILL HOLD HIGH TEMPERATURES IN THE
80S.

PROGRESSING INTO THE WEEKEND...SYNOPTIC EVOLUTION OF THE TROUGH
REMAINS A BIT UNCERTAIN...ALTHOUGH THINGS ARE SLIGHTLY MORE IN LINE
THAN THEY WERE WITH THE TUESDAY 12Z RUNS. THE GFS/GEM/AND GFS
ENSEMBLES ARE ALL PRETTY CLOSE IN SHOWING THE UPPER TROUGH CLOSING
OFF TO THE EAST OF GA/CAROLINA COAST AND THEN PIVOTING NORTHWARD
WITH TIME...LEAVING ONLY A BROAD CYCLONIC FLOW BEHIND OVER THE
PENINSULA. THE ECMWF HAS BEEN INSISTING THAT THIS CLOSED FEATURE
EVOLVES OVER THE FL PENINSULA...AND THEN TAKES ITS TIME LIFTING TO
THE NORTHEAST. WHILE THE ECMWF IS STILL SHOWING THIS PHILOSOPHY...
THE EJECTION OF THE ENERGY IS A BIT FASTER THAN WITH THE 12Z
RUN...AND PERHAPS THIS IS THE BEGINNING OF A TREND TOWARD THE OTHER
GLOBAL MODELS CONSENSUS. WITH THIS IN MIND...WILL FOLLOW CLOSER TO
THE GFS/GEM SOLUTION INTO THE EARLY PORTION OF NEXT WEEK.

NEITHER WEEKEND DAY LOOKS LIKE A WASHOUT...ALTHOUGH SATURDAY COULD
STILL BE ON THE SHOWERY/ MOSTLY CLOUDY SIDE UNDER THE DEEP CYCLONIC
FLOW. WILL SHOW IMPROVEMENT BY SUNDAY WITH CLIMO CHANCES FOR RAIN
SOUTH...AND BELOW CLIMO NORTH. NORTHERN AREAS WILL SEE THE BEST
CHANCE AT ABUNDANT SUNSHINE AS WELL WITH DRIER AIR ALOFT ARRIVING IN
THE WAKE OF THE DEPARTING UPPER LOW.

THE EARLY PORTION OF NEXT WEEK AT THIS POINT LOOKS TO FEATURE NON
EVENTFUL AND NEAR CLIMO CONDITIONS FOR LATER SEPTEMBER. THE UPPER
LEVEL PATTERN SHOULD FLATTEN OUT AS THE DEEPER TROUGHING REMAINS
FURTHER NORTH UP THE EASTERN SEABOARD.

&&

.AVIATION...
17/06Z-18/06Z. BKN MID AND HIGH CLOUDS THROUGH THE EARLY MORNING
WITH VCNTY SHRA AND TSRA. MVFR CIGS BEGIN SPREADING SOUTH AFT 15Z
ALONG WITH HIGHER ODDS OF LCL IFR CONDITIONS...BUT TIMING ISSUES
PRECLUDE INCLUDING TEMPOS WITH THESE TAFS. WINDS LIGHT AND MOSTLY
WESTERLY...BECOMING SW AND WEST DURING THE DAY AT 7-10 KNOTS.

&&

.MARINE...
A FRONTAL BOUNDARY ALONG THE GULF COAST AND HIGH PRESSURE IN THE
GULF WILL MAINTAIN WESTERLY WINDS AS THESE TWO FEATURES MOVE SOUTH
WITH THE BOUNDARY REACHING SOUTH FL TONIGHT. THE BOUNDARY LINGERS
THERE THURSDAY AS HIGH PRESSURE BUILDS IN FROM THE NORTH THEN MOVES
EAST...WITH WINDS TURNING TO EASTERLY. PREVAILING WINDS WILL BE 15
KNOTS OR LESS WITH THE MAIN MARINE CONCERNS SHOWERS AND STORMS WITH
HIGHER WINDS AND SEAS...HEAVY RAINFALL...AND DANGEROUS CLOUD TO
WATER LIGHTNING.

&&

.FIRE WEATHER...
ABUNDANT MOISTURE AND RATHER LIGHT WINDS PRECLUDE ANY FIRE WEATHER
ISSUES.

&&

.PRELIMINARY POINT TEMPS/POPS...
TPA  88  75  91  76 /  70  20  20  20
FMY  90  74  91  74 /  60  40  40  40
GIF  87  72  91  74 /  70  20  30  20
SRQ  87  74  89  75 /  60  40  30  30
BKV  89  68  93  71 /  70  20  20  20
SPG  86  77  90  77 /  70  30  20  30

&&

.TBW WATCHES/WARNINGS/ADVISORIES...
FL...NONE.
GULF WATERS...NONE.
&&

$$

SHORT TERM/AVIATION/MARINE/FIRE WEATHER...09/RUDE
LONG TERM...14/MROCZKA








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