Area Forecast Discussion
Issued by NWS Tampa Bay Area, FL

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FXUS62 KTBW 221521 AAA
AFDTBW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE TAMPA BAY RUSKIN FL
1121 AM EDT FRI AUG 22 2014

.UPDATE...SIMILAR PATTERN ON TAP TODAY AS YESTERDAY ALTHOUGH
MORNING SOUNDING STARTED OFF A BIT MORE MOIST WITH PWS AROUND 1.9
INCHES. LACK OF CU FIELD STILL AT 11 AM SUGGESTS LATE START TO SCT
CONVECTION AGAIN TODAY. SFC RIDGE AXIS REMAINS ACROSS CEN FL WITH VERY
WEAK LOW LEVEL FLOW. INFLUENCE OF MID-UP LEVEL RIDGING IS
PROVIDING ENE FLOW ABOVE H85 OR SO. THIS MEANS THE WEST COAST SEA
BREEZE WILL BE ABLE TO MOVE INLAND INTO INTERIOR COUNTIES BY
AFTERNOON...BUT SIMILAR TO YESTERDAY...ONCE DEEPER CONVECTION
DEVELOPS...IT WILL TEND TO DRIFT BACK TOWARD THE COAST. HIGH
RESOLUTION MODELS INDICATE STRONGEST UPDRAFTS WILL GENERALLY OCCUR
ACROSS INLAND SECTION OF COASTAL COS AND WRN SIDE OF INTERIOR COS
AND THIS IS WHERE HIGHEST POPS ARE SHOWN. LATE START TO STORMS
MEANS ANOTHER HOT DAY WITH HIGHS IN THE MID-UPR 90S AND THIS WILL
PROVIDE MAX HEAT INDEX AROUND 106 IN MANY AREAS WHICH IS JUST
BELOW THE 108 DEGREE THRESHOLD FOR HEAT ADVISORY. HOT TEMPS WILL
ALSO MEAN PROMOTE STRONG CONVECTION WITH LOTS OF LIGHTNING
ALTHOUGH OVERALL COVERAGE OF STORMS IS EXPECTED TO BE LOWER END OF
SCT RANGE FOR ALL BUT FAVORED AREAS MENTIONED ABOVE.

OVERALL MOS POPS CONTINUE TO SHOW A DRY BIAS SIMILAR TO YESTERDAY
AND HIGH RES MODELS SUGGEST HIGHER END SCT RANGE IS MORE
APPROPRIATE AGAIN IN THOSE FAVORED LOCATIONS JUST INLAND MENTIONED
ABOVE. BASED ON THIS...TWEAK POPS UP SLIGHTLY TO 40-50% ALONG AND
JUST EAST OF I-75 FOR SRN 2/3RD OF THE FORECAST AREA. ALSO
REFLECTED THIS IN QPF FORECASTS.

&&

.MARINE...A BROAD AREA OF HIGH PRESSURE REMAINS OVER THE WATERS
CENTERED ROUGHLY AROUND NEW ORLEANS. THIS WILL GIVE THE AREA A
VERY LIGHT NORTH WIND FLOW TODAY WITH DRY AIR AND A JUST A SLIGHT
CHANCE FOR A FEW SHOWERS OR STORMS. EXPECT THE WINDS TO INCREASE
SLIGHTLY LATE IN THE DAY OVER THE NEARSHORE WATERS AS THE SEA
BREEZE ENHANCES THE FLOW NEAR THE COAST. OVER ALL VERY LIGHT WINDS
FOR THE NEXT COUPLE OF DAYS. A WEAK BACK DOOR COLD FRONT MAY
AFFECT THE WEATHER OVER THE NORTHERN WATERS AND BRING CHANCES OF
THUNDERSTORMS EARLY NEXT WEEK. THE WINDS WILL ALSO INCREASE BY
MONDAY AND TUESDAY WITH THE HIGH TO THE NORTH AND THE TROPICAL
SYSTEM PULLING AWAY OVER THE ATLANTIC.

&&

.AVIATION...SCT TSTMS WILL BE MAIN ISSUE FOR TAF SITES THIS AFTN.
PEAK TIMING WILL BE 4 TO 8 PM SIMILAR TO YESTERDAY WITH HIGHEST
PROBS ACROSS SITES NEAREST TO I-75. HANDLED THIS WITH VCTS FOR NOW
AND WILL UPDATE AS NEEDED ONCE STORMS BEGIN TO DEVELOP. AS ALWAYS
BRIEF IFR CONDITIONS ARE POSSIBLE BY SITES IMPACTED BY TSTMS...BUT
THESE ARE VERY LOW PROBABILITY EVENTS AND GENERALLY SHORT LIVED.

&&

.PREV DISCUSSION... /ISSUED 354 AM EDT FRI AUG 22 2014/

SHORT TERM (TODAY-SATURDAY)...
THE MID/UPPER LEVEL RIDGE WILL REMAIN CENTERED OVER THE LOWER
MISSISSIPPI VALLEY WITH SOME WEAK SUBSIDENCE REMAINING OVER THE
REGION. MEANWHILE AT THE SURFACE THE RIDGE WILL HOLD ACROSS THE
GULF OF MEXICO AND FLORIDA KEEPING A RATHER LIGHT FLOW IN PLACE
WITH THE SEA BREEZES DEVELOPING EACH AFTERNOON. GUIDANCE CONTINUES
TO INDICATE PLENTY OF MOISTURE ACROSS THE AREA...PRECIPITABLE
WATER VALUES GENERALLY BETWEEN 1.7 AND 1.9 INCHES...AND WITH THE
GENERAL STEERING FLOW OUT OF THE EAST TO NORTHEAST WE SHOULD SEE
SCATTERED CONVECTION POP UP EACH AFTERNOON AND THEN DRIFT BACK
TOWARD THE WEST COAST IN THE EVENING. FOR TODAY THE HIGHEST RAIN
CHANCES SHOULD BE OVER SOUTHWEST FLORIDA...BUT LIKE YESTERDAY
INLAND AREAS FURTHER NORTH SHOULD AT LEAST SEE LOW END SCATTERED
POPS. TONIGHT ANY CONVECTION WILL DRIFT WEST OUT INTO THE GULF
DURING THE EVENING WITH MOSTLY CLEAR TO PARTLY CLOUDY SKIES
PREVAILING. ON SATURDAY WE WILL ONCE AGAIN SEE SCATTERED
CONVECTION DEVELOP DURING THE AFTERNOON AND EVENING AS THE SEA
BREEZES MOVE INLAND WITH MORE CONVECTION POPPING ALONG OUTFLOW
BOUNDARIES AND DRIFTING BACK TOWARD THE GULF COAST DURING THE
EVENING.

TEMPERATURES WILL CONTINUE TO BE THE BIG STORY AS DAYTIME HIGHS
ARE FORECAST TO ONCE AGAIN CLIMB INTO THE LOWER TO MID 90S...
POSSIBLY UPPER 90S IN A FEW INLAND LOCATIONS TODAY AND SATURDAY.
THESE TEMPERATURES COMBINED WITH THE HUMIDITY WILL LEAD TO HEAT
INDICES GENERALLY IN THE 101 TO 106 RANGE...BUT WOULD NOT BE
SURPRISED TO SEE A FEW SITES CLIMB TO NEAR 110. HEAT ADVISORY
CRITERIA IS FOR HEAT INDICES OF 108 TO 112...BUT THESE VALUES
SHOULD BE OVER A LARGE AREA NOT JUST A FEW SITES HERE AND THERE.
OVERNIGHT LOWS TONIGHT WILL FALL INTO THE 70S TO AROUND 80 DEGREES.

LONG TERM (SATURDAY NIGHT-FRIDAY)...
WITH THE EXCEPTION OF THE CANADIAN MODEL...GUIDANCE HAS CHANGED
LITTLE SINCE THIS TIME YESTERDAY. MOST MODELS CONTINUE TO TURN
DISTURBANCE 96L NORTHWARD AND NORTHEASTWARD NEAR THE EASTERN
BAHAMAS WHILE THE CANADIAN HAS SHIFTED FAR TO THE SOUTH...
SKIRTING THE NORTH COAST OF CUBA AS IT HEADS INTO THE CENTRAL
GULF. THE CANADIAN MODEL IS BEING DISCOUNTED AT THIS TIME. WE WILL
CONTINUE TO MONITOR MODEL TRENDS AND THE LATEST INFORMATION FROM
THE NATIONAL HURRICANE CENTER AS THIS SYSTEM DEVELOPS.

FOR SUNDAY...A WEAK BACK-DOOR COLD FRONT WILL BE MOVING SOUTH
THROUGH THE PENINSULA WHICH MAY SERVE TO ENHANCE RAIN CHANCES
SOMEWHAT. BEST MOISTURE WILL BE ALONG THE FRONTAL BOUNDARY SO
HIGHEST RAIN CHANCES WILL BE OVER OUR NORTHERN COUNTIES...BUT
THERE WILL LIKELY BE SCATTERED AFTERNOON STORMS THROUGHOUT THE
REGION.

FOR MONDAY AND TUESDAY...WE SHOULD BE UNDER THE INFLUENCE OF A
TIGHTENING PRESSURE GRADIENT BETWEEN HIGH PRESSURE TO THE NORTH
AND THE TROPICAL DISTURBANCE TO OUR EAST. DRIER AIR WILL TRY TO
WORK IN FROM THE NORTH...BUT IT DOES NOT LOOK LIKE IT WILL BE
ENOUGH TO SHUT DOWN OUR AFTERNOON RAIN CHANCES. STRENGTHENING
EASTERLY FLOW WILL BRING THE EAST COAST SEA BREEZE ALL THE WAY
ACROSS TO THE GULF COAST RESULTING IN HIGHER RAIN CHANCES ALL THE
WAY TO THE BEACHES.

THE PRESSURE GRADIENT SHOULD RELAX AGAIN BY MID WEEK AS WHATEVER
BECOMES OF THE TROPICAL DISTURBANCE LIFTS AWAY TO THE NORTHEAST.
THIS WILL ALLOW OUR WEST COAST SEA BREEZE TO BECOME MORE DOMINANT
AND PUSH HIGHEST RAIN CHANCES INLAND EACH AFTERNOON WEDNESDAY
THROUGH FRIDAY.

AVIATION...
SOME MVFR/LOCAL IFR CONDITIONS WILL BE POSSIBLE IN SCATTERED
SHOWERS AND THUNDERSTORMS THIS AFTERNOON AND EVENING...OTHERWISE
VFR CONDITIONS SHOULD PREVAIL.

MARINE...
THE GENERAL NORTHWESTERLY FLOW WILL PERSIST THROUGH THE WEEKEND
AS HIGH PRESSURE REMAINS OVER THE GULF OF MEXICO. EARLY NEXT WEEK
WINDS WILL BECOME EAST TO NORTHEAST AS A BACK DOOR COLD FRONT
MOVES INTO THE AREA AND HIGH PRESSURE BRIDGES THE BOUNDARY. WINDS
ARE EXPECTED TO REMAIN 15 KNOTS OR LESS AND SEAS LESS THAN 4 FEET
THROUGH THE WEEKEND...THEN EARLY NEXT WEEK THE EAST TO NORTHEAST
FLOW COULD INCREASE TO EXERCISE CAUTION CRITERIA.

FIRE WEATHER...
NO FIRE WEATHER CONCERNS EXPECTED THROUGH THE WEEKEND AS RELATIVE
HUMIDITY VALUES SHOULD REMAIN ABOVE CRITICAL THRESHOLDS. COULD SEE
SOME PATCHY GROUND FOG LATE EACH NIGHT...ESPECIALLY IN LOCATIONS
THAT RECEIVE RAIN DURING THE PREVIOUS EVENING.

&&

.PRELIMINARY POINT TEMPS/POPS...
TPA  93  79  93  80 /  40  20  30  20
FMY  95  76  95  78 /  50  20  30  20
GIF  96  77  96  78 /  30  10  30  10
SRQ  93  77  93  79 /  30  20  30  20
BKV  95  74  95  74 /  40  20  30  20
SPG  93  79  93  82 /  30  20  30  20

&&

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

$$

UPDATE/AVIATION/FIRE WEATHER...88/GITTINGER
MARINE...007/DOUGHERTY
DECISION SUPPORT...02/GARCIA




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