Spring Hill, Florida Area

[ROLLTIDE]

000
FXUS62 KTBW 231733
AFDTBW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAMPA BAY RUSKIN FL
133 PM EDT WED SEP 23 2009

.SYNOPSIS...ALOFT NORTH AMERICA EARLY THIS AFTERNOON - A RIDGE
REACHES FROM SW CANADA TO SOUTH CA...A LOW SPINS ALONG THE NE/KS
BORDER...TROUGHING OVER EASTERN CANADA BRUSHES NEW ENGLAND...AND
A RIDGE STRETCHES FROM MEXICO TO THE SE U.S. AT THE SURFACE...A
LOW IS OVER EASTERN NE/KS WITH A FRONT SOUTH TO TX. A STATIONARY
FRONT EXTENDS FROM TX COASTAL WATERS TO THE LOWER GREAT LAKES.
HIGH PRESSURE OVER THE OPEN ATLANTIC ALONG LATITUDE 40 NORTH RIDGES
TO THE U.S. COAST BETWEEN FL AND THE MID-ATLANTIC STATES. AN
INVERTED TROUGH...THE REMNANTS OF FRED...EMBEDDED IN THE SOUTH SIDE
OF THE SURFACE RIDGE IS ALONG THE FL TO NC COAST.

&&

.SHORT TERM (TONIGHT - FRIDAY)...THE PATTERN ALOFT THE NATION
CHANGES LITTLE WITH THE UPPER RIDGE DOMINATING AS IT SETTLES
SOUTHWARD ACROSS THE AREA. THE INVERTED TROUGH/REMNANTS OF FRED/
DISSIPATES AS IT LIFTS UP TO THE NW WHILE THE ATLANTIC HIGH PRESSURE
WEAKENS AND SAGS SOUTH...ALLOWING THE GRADIENT TO SLACKEN WITH
EASTERLY FLOW OVER FL AND THE GULF.

THE EAST COAST MORNING CONVECTION DISSIPATED FOR THE MOST PART
BEFORE REACHING THE CWA. HOWEVER..A FEW SHOWERS SHOWERS AND THUNDER-
STORMS ARE NOW OVER AND EAST OF CHARLOTTE AND LEE COUNTIES. WITH
THE MOIST ATMOSPHERE AND THE EXPECTED SEA BREEZE...THE CURRENT POPS
OF 30-50-40 FROM COASTAL WATERS TO INTERIOR SEEM REASONABLE AND WILL
LEAVE AS IS. ACTIVITY WILL BECOME ISOLATED AND THEN END IN THE EARLY
EVENING. LIGHT ENE WINDS ALONG WITH ANY RESIDUAL MOISTURE COULD
RESULT IN LATE NIGHT PATCHY FOG FROM PINELLAS...HILLSBOROUGH...AND
POLK NORTH AND PLACED IN THE GRIDS AND FORECASTS.

FOR THU AND FRI...THE PATTERN CONTINUES WITH SCATTERED AFTERNOON...
ISOLATED EVENING SHOWERS/THUNDERSTORMS AS THE SEA BREEZE BOUNDARY
PROVIDES A FOCUS. THE UPPER RIDGE SHIFTING SOUTH WILL SUPPRESS
POPS FROM 40/50 THU TO 30 FRI. IN ADDITION THE RIDGE WILL HELP
KEEP TEMPERATURES ABOVE NORMAL BY A COUPLE OF DEGREES.

.LONG TERM (FRIDAY NIGHT - WEDNESDAY)...MODELS REMAIN FAIRLY
CONSISTENT DURING THE FIRST HALF OF THE LONG TERM...THEN DIFFER SOME
WITH RESPECT TO TIMING AND SPEED OF THE NEXT UPSTREAM COLD FRONT
PROGD TO APPROACH THE REGION LATE IN THE WEEKEND AND INTO EARLY NEXT
WEEK WITH THE ECMWF CONTINUING TO BE FASTER THAN THE GFS. GIVEN THE
DIFFERENCES WILL CONTINUE WITH A BLEND FOR NOW UNTIL BETTER MODEL
CONTINUITY DEVELOPS.

AS FOR THE DETAILS OF THE FORECAST DEEP LAYERED RIDGING OVER THE DEEP
SOUTH AND FLORIDA WITH A SURFACE RIDGE AXIS WELL TO THE NORTH WILL
REMAIN IN CONTROL THROUGH EARLY MONDAY. DRY AIR ADVECTING IN FROM
THE ATLANTIC COMBINED WITH INCREASED SUBSIDENCE FROM THE UPPER RIDGE
WILL KEEP RAIN CHANCE BELOW NORMAL (POPS 20% AT BEST) AND
TEMPERATURES ABOVE NORMAL THROUGH THE PERIOD.

DURING EARLY NEXT WEEK A DEVELOPING UPPER TROUGH OVER THE EASTERN
U.S. WILL SUPPRESS THE UPPER RIDGE SOUTHWARD AS AN ATTENDANT COLD
FRONT MOVES INTO THE DEEP SOUTH. AS MENTIONED ABOVE DIFFERENCES IN
THE MODELS LEADS TO LOW CONFIDENCE AND SOME UNCERTAINTY IN THE
FORECAST WITH RESPECT TO JUST HOW FAR SOUTH THIS FRONT WILL MOVE.
SEEING THAT MOST OF THE UPPER SUPPORT ASSOCIATED WITH IT WILL REMAIN
WELL TO THE NORTH OF THE REGION CONTINUE TO PREFER THE SLOWER
LOOKING GFS SOLUTION WITH THE FRONT LIKELY TO STALL AND WASH OUT
ACROSS THE CENTRAL PENINSULA ON TUESDAY. GIVEN THIS WILL DEPICT POPS
IN THE 30-40% RANGE OVER THE NATURE COAST ON MONDAY WITH 20% POPS
CONTINUING CENTRAL AND SOUTH...THEN WILL SHOW A 20-40% POP GRADIENT
SOUTH TO NORTH ON TUESDAY AS THE FRONT SAGS INTO THE REGION. MODELS
STILL SHOW SIGNIFICANTLY DRIER AIR MOVING INTO WEST CENTRAL FLORIDA
ON WEDNESDAY IN THE WAKE OF THE FRONT AS SURFACE HIGH PRESSURE
BUILDS IN FROM THE NORTH. TEMPERATURES WILL REMAIN ABOVE NORMAL
THROUGH TUESDAY...THEN RETURN TO NEAR NORMAL ON WEDNESDAY.

&&

.AVIATION...BRIEF MVFR CEILINGS AND VISIBILITIES MAY IMPACT THE
TERMINAL SITES FROM MID AFTERNOON (AFTER 20Z) ON THROUGH THE EARLY
EVENING AS SCATTERED SHOWERS AND ISOLATED STORMS DEVELOP OVER THE
REGION. OUTSIDE OF THE CONVECTION VFR CONDITIONS ARE EXPECTED. THE
SHOWERS AND STORMS WILL WIND DOWN BY MID EVENING TONIGHT...WITH VFR
CONDITIONS EXPECTED AT ALL TERMINAL SITES OVERNIGHT...BUT SIMILAR TO
THIS MORNING MAY AGAIN SEE SOME BRIEF IFR/LIFR CEILINGS DEVELOP
TOWARD SUNRISE ON THURSDAY MORNING NEAR KTPA/KPIE TERMINALS.

&&

.MARINE...HIGH PRESSURE CONTINUES OVER THE COASTAL WATERS THROUGH
THE END OF THE WEEK WITH EASTERLY WINDS...EXCEPT SHIFTING TO ONSHORE
IN AFTERNOON SEA BREEZES NEAR THE COAST. THE HIGH PRESSURE WILL SAG
SOUTH DURING THE WEEKEND AND MON WITH WINDS BECOMING SE AND THEN
SW OR WEST. SPEEDS WILL BE AROUND 10KT OR LESS WITH THE MAIN
CONCERN ISOLATED TO SCATTERED THUNDERSTORMS.

&&

.FIRE WEATHER...NO CONCERNS.

&&

.PRELIMINARY POINT TEMPS/POPS...
TPA 75 91 76 92 / 20 50 20 30
FMY 76 92 74 92 / 20 50 20 30
GIF 74 92 75 93 / 20 40 20 30
SRQ 74 90 74 92 / 20 50 20 30
BKV 73 91 73 92 / 20 50 20 30
SPG 78 90 79 90 / 20 50 20 30

&&

.TBW WATCHES/WARNINGS/ADVISORIES...
FL...NONE.