River Flood Warning 28, NWS Tampa Bay, FL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAMPA BAY RUSKIN FL
300 PM EDT FRI SEP 6 2013

...STRONG TO POTENTIALLY SEVERE STORMS POSSIBLE LATER THIS AFTERNOON
AND EVENING...

.SHORT TERM...
STRONG TSTMS HAVE BEEN ONGOING ALONG THE SPACE COAST THIS AFTERNOON
WITH A FEW MORE STORMS CURRENTLY OVER PORTIONS OF CITRUS AND
HERNANDO COUNTIES. GROWING INCREASINGLY CONCERNED OVER POTENTIAL OF
STRONG TO SEVERE TSTMS OVER PORTIONS OF THE FORECAST AREA. A
MODERATELY UNSTABLE AIRMASS EXISTS ACROSS THE FLORIDA PENINSULA THIS
AFTERNOON WITH MLCAPE VALUES OF 2000-3000 J/KG. THIS COMBINED WITH A
VERY MOIST BOUNDARY LAYER...AS EVIDENT ON THE MORNING KTBW RAOB
SHOULD ALLOW FOR THE POTENTIAL OF STRONG TO SEVERE TSTM DEVELOPMENT.
EXCESSIVE LIGHTNING...DAMAGING WINDS AND SOME HAIL WILL BE POSSIBLE
ALONG WITH VERY HEAVY RAINFALL. LATEST HRRR MODEL RUN SEEMS TO HAVE
A GRASP ON THE CURRENT CONVECTIVE ACTIVITY OVER THE PENINSULA. IT
SUGGESTS THAT THE BULK OF THE TSTMS CURRENTLY OVER ORANGE...LAKE AND
SEMINOLE COUNTIES WILL GRADUALLY MOVE INTO THE CWA OVER THE NEXT
HOUR OR SO. THE HRRR GUIDANCE SUGGEST THAT A SOMEWHAT LINEAR BAND OF
TSTMS WILL MOVE INTO INTERIOR SECTIONS OF THE AREA AROUND 21-22Z.
THE TAMPA BAY METRO AREA WILL LIKELY SEE ITS BEST CHANCE OF TSTM
ACTIVITY AROUND 23Z AND STORMS SHOULD BEGIN TO EXIT THE COAST AROUND
1-2Z THIS EVENING WITH LINGERING SHOWERS POSSIBLE OVER LAND AREAS
INTO THE EARLY OVERNIGHT HOURS.

SOMEWHAT DRIER AIR WILL MOVE INTO THE AREA TOMORROW WHICH COULD
SERVE AS LIMITING FACTOR FOR SHOWER AND TSTM COVERAGE UNTIL A TAD
LATER INTO THE AFTERNOON. NORTHERN ZONES WILL SEE THE DRIER AIR
FIRST AND BECAUSE OF THIS...LOWER RAIN CHANCES ARE FORECAST FOR THE
NATURE COAST NORTHWARD. STILL FEEL ENOUGH MOISTURE WILL BE IN PLACE
FROM TAMPA BAY SOUTH TO KEEP AROUND 40 POPS IN PLACE.

ON SUNDAY THE DRY AIR BECOMES WELL ESTABLISHED OVER MOST OF THE
REGION. MODELS STILL SHOW SOME POTENTIAL FOR SEA BREEZE INITIATED
STORMS...BUT THE OVERALL COVERAGE SHOULD BE QUITE A BIT LOWER THAN
TODAY AND SATURDAY WITH HIGHEST RAIN CHANCES DOWN SOUTH.

.LONG TERM (MONDAY THROUGH NEXT THURSDAY)...
LONG TERM PERIOD WILL BEGIN NEXT MONDAY WITH A PATTERN DOMINATED BY
LARGE SCALE UPPER RIDGING CENTERED OVER THE SE CONUS. RESIDUAL
ENERGY / WEAK TROUGHING LOOKS TO LINGER FROM OFF THE CAROLINA COAST
SOUTH AND SOUTHWEST TO THE SOUTHERN PORTION OF THE FLORIDA
PENINSULA. WEAK SUPPRESSION FROM THE UPPER RIDGE ALONG WITH THE
ADVECTION OF DRIER AIR DOWN FROM THE NORTH AND NORTHEAST AROUND THE
SYNOPTIC CIRCULATION LOOKS TO BRING SOME LESS FAVORABLE ATMOSPHERIC
CONDITIONS FOR DEEP CONVECTION TO PORTION OF THE AREA DURING THE
FIRST HALF OF THE WORK WEEK. BOTH THE GFS/ECMWF AGREE ON THE DRY AIR
BECOMING ENTRENCHED OVER THE NORTHERN HALF OF THE FORECAST
AREA...HOWEVER THE GFS IS MORE DRAMATIC WITH THIS DRYING...AND ALSO
MORE EXPANSIVE WITH THE DRIER MID-LEVEL AIR TO THE SOUTH.

EITHER WAY...A DECREASE IN THE OVERALL COVERAGE OF SHOWERS AND
STORMS FROM WHAT IS FORECAST OVER THE WEEKEND LOOKS LIKELY. BEST
CHANCES FOR SCATTERED AFTERNOON/EVENING STORMS MONDAY THROUGH
WEDNESDAY EXISTS SOUTH OF I-4...AND ESPECIALLY FROM PUNTA GORDA
SOUTHWARD...WHERE THE MORE "FAVORABLE" MOISTURE PROFILE WILL BE
COINCIDENT WITH EASTERLY LOW LEVEL FLOW TO FOCUS SEA-BREEZE
CONVERGENCE. EVEN STILL...ONLY GOING WITH 30-40% RAIN CHANCES FOR
THESE SOUTHERN ZONES...AND LESSER 20-30% RAIN CHANCES FOR THE
CENTRAL AND NATURE COAST ZONES. WITH THE UPPER RIDGE NEARBY...AND
THE POTENTIAL FOR LESS CONVECTIVE COVERAGE...DAYTIME TEMPS SHOULD
AVERAGE OUT A BIT ABOVE NORMAL.

DURING THE LAST COUPLE DAYS OF THE FORECAST PERIOD...THERE IS SOME
INDICATIONS IN THE GLOBAL GUIDANCE OF A SLOW RETURN OF DEEP MOISTURE
FROM THE EAST AND SOUTHEAST. ONCE AGAIN...THE GFS IS THE MOST
STUBBORN TO HOLD ON TO THE DRIER AIR (ESPECIALLY FROM TAMPA
NORTHWARD)...WHILE THE ECMWF RETURNS THE ENTIRE REGION TO A MORE
FAVORABLE COLUMN FOR DEEP CONVECTION BY FRIDAY. MID/UPPER LEVEL
MOISTURE FIELDS CAN BE SOMEWHAT QUESTIONABLE IN NWP GUIDANCE AT THE
LONGER RANGES...AND CERTAINLY WOULD NOT WANT TO "HANG MY HAT" ON ANY
ONE MODEL SOLUTION. WILL BLEND THE MORE RELIABLE SOLUTION...WHICH
SUGGESTS CHANCE 30-40% POPS FOR BOTH THURSDAY AND FRIDAY. MORE
MOISTURE SUCH AS THE ECMWF ADVERTISES WOULD LEAD TO HIGHER POPS BY
FRIDAY...AND LESS FAVORABLE CONDITIONS AS THE GFS ADVERTISES WOULD
LEAD TO LOWER POPS...ESPECIALLY FOR THE NATURE COAST ZONES.

&&

.AVIATION...
VFR CONDITIONS CURRENTLY PREVAIL ACROSS WEST-CENTRAL AND SOUTHWEST
FLORIDA WITH VCTS AT ALL TERMINALS THROUGH 01Z. I HAVE INCLUDED A
TEMPO GROUP FOR BRIEF MVFR/IFR CEILINGS AND VISIBILITIES AT ALL
TERMINAL SITES BETWEEN 06/21Z AND 06/24Z AS SCATTERED SHOWERS AND
STORMS DEVELOP OVER THE REGION. WINDS WILL BE VARIABLE IN VICINITY
OF THUNDERSTORMS WITH POSSIBLE STRONG GUSTS NEAR 40 KNOTS. STORMS
WILL DIMINISH BY 07/01Z...LEAVING PREVAILING VFR CONDITIONS ONCE
AGAIN UNDER A SCT-BKN HIGH LEVEL CIRRUS CANOPY.

&&

.MARINE...
HIGH PRESSURE CONTINUES TO PROVIDE EASTERLY FLOW THROUGH INTO NEXT
WEEK OVER THE WATERS. SHOWERS AND THUNDERSTORMS ARE EXPECTED MOST
DAYS...WITH LATE AFTERNOON AND EVENING THUNDERSTORMS COMING FROM THE
EAST POTENTIALLY CREATING HIGHER WINDS AND WAVES FOR MARINERS.
OTHERWISE...THERE MIGHT BE SOME WINDS AND WAVES NEARING CAUTIONARY
CRITERIA EARLY NEXT WEEK DUE TO OVERNIGHT EASTERLY WIND SURGES.

&&

.FIRE WEATHER...NO SIGNIFICANT FIRE WEATHER PROBLEMS BUT STAGNANT
HIGH PRESSURE OVER THE REGION WILL FAVOR LIGHT WINDS AND LIGHT
TRANSPORT WINDS RESULTING IN LOW DISPERSIONS FOR THE NEXT COUPLE
OF DAYS.

&&

.PRELIMINARY POINT TEMPS/POPS...
TPA  76  92  74  90 /  30  30  20  30
FMY  75  92  74  92 /  40  40  30  40
GIF  74  94  71  93 /  20  30  10  20
SRQ  75  92  73  91 /  30  30  20  30
BKV  70  92  69  92 /  30  30  20  20
SPG  79  90  77  89 /  30  30  20  30

&&

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

SHORT TERM/FIRE WEATHER...11/MCKAUGHAN
LONG TERM...14/MROCZKA
AVIATION...74/WYNN
MARINE...02/GARCIA

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE TAMPA BAY RUSKIN FL
1156 AM EDT FRI SEP 6 2013

FLZ039-042-043-048>052-055>057-060>062-065-GMZ830-850-853-856-870-
873-876-070500-
LEVY-CITRUS-SUMTER-HERNANDO-PASCO-PINELLAS-HILLSBOROUGH-POLK-
MANATEE-HARDEE-HIGHLANDS-SARASOTA-DESOTO-CHARLOTTE-LEE-
TAMPA BAY WATERS-TARPON SPRINGS TO SUWANNEE RIVER OUT 20 NM-
ENGLEWOOD TO TARPON SPRINGS OUT 20 NM-
BONITA BEACH TO ENGLEWOOD OUT 20 NM-
TARPON SPRINGS TO SUWANNEE RIVER OUT 20 TO 60 NM-
ENGLEWOOD TO TARPON SPRINGS OUT 20 TO 60 NM-
BONITA BEACH TO ENGLEWOOD OUT 20 TO 60 NM-
1156 AM EDT FRI SEP 6 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WEST CENTRAL AND SOUTHWEST
FLORIDA.

.DAY ONE...THIS AFTERNOON AND TONIGHT.

...THUNDERSTORM IMPACT...
A LIGHT FLOW NORTH AND WEAK EASTERLY FLOW SOUTH WILL KEEP THE SEA
BREEZE FROM MOVING INLAND ALL THAT RAPIDLY THIS AFTERNOON. AMPLE
MOISTURE AND INSTABILITY WILL COMBINE WITH DAYTIME HEATING...THE
SEA BREEZES AND OUTFLOW BOUNDARIES TO CAUSE SCATTERED TO NUMEROUS
AFTERNOON AND EVENING THUNDERSTORMS.

THE MAIN HAZARDS WITH THE STRONGER STORMS WILL BE LOCALLY HEAVY
RAINFALL...DAMAGING DOWNBURST WINDS...FREQUENT CLOUD TO GROUND
LIGHTNING...AND PEA TO QUARTER SIZED HAIL. DUE TO SATURATED
SOILS...ANY SLOW MOVING STORMS ARE LIKELY TO RESULT IN LOCALIZED
STREET AND SMALL STREAM FLOODING. FUNNEL CLOUDS AND WATERSPOUTS
CANNOT BE RULED OUT LATER TODAY...PARTICULARLY ALONG THE COAST
FROM TAMPA BAY SOUTHWARD WHERE BOUNDARY COLLISIONS ARE EXPECTED TO
OCCUR.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY.

...THUNDERSTORM IMPACT...
A CONTINUED ACTIVE PATTERN OF AFTERNOON AND EVENING SHOWERS AND
STORMS SHOULD CONTINUE ON SATURDAY. THEREAFTER DURING THE SECOND
HALF OF THE WEEKEND AND EARLY PORTION OF NEXT WEEK...DRIER AIR
ARRIVING ALOFT SHOULD HELP TO DECREASE THE COVERAGE OF DAILY
SHOWERS AND STORMS.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS SHOULD MONITOR THE WEATHER AND SELF ACTIVATE IF NEEDED.

GARCIA