Area Forecast Discussion
Issued by NWS Tampa Bay Area, FL

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FXUS62 KTBW 231904
AFDTBW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAMPA BAY RUSKIN FL
304 PM EDT SAT AUG 23 2014

...ALL EYES WILL REMAIN FOCUSED ON THE TROPICS...

.SHORT TERM (TONIGHT - SUNDAY)...
AMPLE LOW LEVEL MOISTURE AND INSTABILITY SHOULD ALLOW FOR SCATTERED
SHOWER AND STORM DEVELOPMENT ACROSS THE REGION THE REMAINDER OF THE
AFTERNOON ALONG THE SEA BREEZE AND OUTFLOW BOUNDARIES. AS MENTIONED
IN THE MORNING DISCUSSION DRIER AIR ALOFT AND STEEP LAPSE RATES MAY
RESULT IN STRONG DOWNBURST WINDS WITH SOME OF THE STRONGEST STORMS.
FREQUENT LIGHTNING STRIKES AND HEAVY RAINS WILL ALSO ACCOMPANY THE
STORMS AS THEY MOVE TO WEST AND SOUTHWEST INTO THE EARLY EVENING
HOURS.

TONIGHT THE CONVECTION SHOULD SLOWLY WIND DOWN AFTER SUNSET WITH
LOSS OF DAYTIME HEATING AND WEAKENING BOUNDARY INTERACTIONS WITH
CONVECTIVE DEBRIS CLOUDINESS THINNING WITH SKIES BECOMING PARTLY
CLOUDY OVERNIGHT. TEMPERATURES TONIGHT WILL REMAIN ABOVE NORMAL
WITH OVERNIGHT LOWS RANGING FROM THE MID 70S OVER INLAND AREAS TO
THE UPPER 70S TO LOWER 80S ALONG THE IMMEDIATE COAST.

ON SUNDAY DEEP LAYERED RIDGING OVER THE MS/TN VALLEYS EXTENDING
SOUTH INTO THE NORTHERN GULF WILL REMAIN IN CONTROL AS A TROPICAL
DISTURBANCE NOW JUST NORTH OF HISPANIOLA THIS AFTERNOON DRIFTS WEST
NORTHWEST INTO THE CENTRAL BAHAMAS...WHILE A BACK-DOOR TYPE COLD
FRONT SAGS SOUTHWEST INTO THE NORTHERN PENINSULA IN THE VICINITY OF
KJAX DURING THE AFTERNOON AS THE UPPER TROUGH OVER THE WESTERN
ATLANTIC AMPLIFIES SOME. SIMILAR TO TODAY AMPLE LOW LEVEL MOISTURE
AND GOOD INSTABILITY COMBINED WITH THE PRESENCE OF THE FRONT TO THE
NORTH SHOULD ALLOW SCATTERED SHOWERS AND THUNDERSTORMS TO DEVELOP
ACROSS THE REGION FROM LATE MORNING INTO THE AFTERNOON. WITH THE
TROPICAL DISTURBANCE TO THE SOUTHEAST AND HIGH PRESSURE TO THE NORTH
AND WEST A TIGHTER PRESSURE GRADIENT SHOULD MATERIALIZE WHICH SHOULD
SUPPORT AN SLIGHTLY STRONGER NORTHEAST TO EASTERLY BOUNDARY LAYER
FLOW. THIS FLOW SHOULD TEND TO HOLD THE WEST COAST SEA BREEZE ALONG
OR JUST WEST OF THE I-75 CORRIDOR DURING THE AFTERNOON...AND THIS IS
WHERE THE BEST CONVERGENCE LIFT AND HIGHEST POPS WILL DEPICTED. IT
WILL CONTINUE HOT AND MUGGY ON SUNDAY WITH DAYTIME HIGHS AGAIN
SOARING INTO THE LOWER 90S ALONG THE COAST AND MID TO UPPER 90S
INLAND AREAS PRIOR TO THE ONSET OF CONVECTION WITH HEAT INDICES
CLIMBING INTO THE 105-106 DEGREE RANGE. THE MAV/MET AND EURO
TEMPERATURE GUIDANCE IS VERY CLOSE SO A BLEND WILL BE USED.


.LONG TERM (SUNDAY NIGHT - FRIDAY)...
WELL...A CHALLENGING LONG RANGE FORECAST TO SAY THE LEAST. ALL
EYES ARE ON A VIGOROUS TROPICAL DISTURBANCE NEAR HISPANIOLA EARLY
THIS MORNING. MOST NWP GUIDANCE MEMBERS WANT TO BEGIN DEVELOPING
THIS SYSTEM (TO VARYING DEGREES) ONCE IT IS FREE FROM THE HOSTILE
HIGHER TERRAIN OF HISPANIOLA LATER TODAY...AND SLOWLY MOVING THE
SYSTEM TOWARD THE BAHAMAS OVER THE WEEKEND.

HERE IS THE DEAL WITH NWP AND TROPICAL CYCLONES. OVERALL NWP IS NOT
SO GOOD AT DEALING WITH STORMS THAT HAVE NOT BECOME WELL-DEFINED
(AND THIS ONE IS NOT WELL DEFINED AS OF NOW). SO...YOU NEED TO TAKE
ANY OF THE VARIOUS SOLUTIONS WITH SOME SKEPTICISM...SOMEWHAT WITH
THE TRACK OF THE POTENTIAL STORMS...AND VERY MUCH SO WITH THE
STRENGTH. WHAT WE CAN SAY IS THAT THE RELIABLE GLOBAL GUIDANCE KEEP
"THE SYSTEM" TO THE EAST OF THE FLORIDA PENINSULA AS IT IS DRAGGED
NORTH INTO AN AMPLIFYING LONGWAVE TROUGH OFF THE
NORTHEAST/MID-ATLANTIC COAST EARLY NEXT WEEK. EVEN THE GEM WHICH HAD
BEEN MUCH FURTHER WEST HAS TRENDED BACK TO THE EAST AND KEEPS THIS
POTENTIAL SYSTEM WELL EAST OF THE FL PENINSULA. WE STILL NEED TO
KEEP A VERY CLOSE EYE ON THIS SYSTEM REGARDLESS...BUT FOR NOW...THE
FORECAST WILL REFLECT A SCENARIO TAKING A CIRCULATION NEAR THE
BAHAMAS AND THEN NORTHWARD OFF THE SOUTHEAST CONUS COAST THROUGH THE
EARLY/MIDDLE PORTION OF NEXT WEEK. WILL NOT GO OVERLY DETAILED WITH
ANY PORTION OF THE FORECAST AS SO MANY POTENTIAL SCENARIOS ARE STILL
IN PLAY.

FOR INSTANCE...A STRONGER/MORE ORGANIZED SYSTEM OFF THE SOUTHEAST
COAST EARLY NEXT WEEK COULD ACTUALLY RESULT IN LARGE SCALE
SUBSIDENCE OVER OUR REGION AND LOWER RAIN CHANCES...BUT WOULD
TIGHTEN THE SYNOPTIC GRADIENT OVER THE EASTERN GULF OF MEXICO
BETWEEN THE SYSTEM AND RIDGING TO OUR NORTH...PRODUCING STRONGER
WINDS ACROSS THE COASTAL WATERS. HOWEVER...AS WAS SAID
ABOVE...FORECASTING STRENGTH OF TROPICAL CYCLONES IN THE EARLY
STAGES OF DEVELOPMENT IS NOT SOMETHING NWP DOES A PARTICULARLY GOOD
JOB AT. WILL DO MY BEST TO COME UP WITH A MOST LIKELY SCENARIO FOR
THE EXTENDED PORTION OF THE FORECAST AS IT STANDS NOW...AND WE WILL
SIMPLY ADJUST AS EVENTS UNFOLD.

KEEPING WITH THE IDEAS OF AN TROPICAL SYSTEM TO OUR EAST MOVING
NORTHWARD OFF THE SOUTHEAST CONUS COAST...WILL HAVE EAST/NORTHEAST
FLOW THROUGH THE EARLY AND MIDDLE PORTION OF THE WEEK. BASED ON THE
LIKELIHOOD OF SOME DRIER AIR ARRIVING FROM THE NORTHEAST ABOVE THE
SURFACE (ESPECIALLY OVER THE NORTHERN HALF OF THE STATE)...WILL HAVE
GENERALLY NEAR CLIMO RAIN CHANCES FOR OUR SOUTHERN ZONES AND BELOW
CLIMO FOR THE NORTH.

TOWARD THE END OF NEXT WEEK...THE SUBTROPICAL RIDGE IS SHOWN BY BOTH
THE GFS/ECMWF TO REBUILD INTO THE SOUTHERN HALF OF THE PENINSULA AND
PROVIDE A LIGHT SW LOW LEVEL FLOW. THIS PATTERN SUGGEST MORNING
SHOWERS OVER THE GULF AND COASTAL LAND ZONES...WITH BEST CHANCES FOR
SHOWERS AND STORMS MIGRATING INLAND FOR THE AFTERNOON/EVENING
HOURS.

&&

.AVIATION...
DEVELOPING SCATTERED SHRA/TSRA MAY BRING BRIEF TEMPO MVFR CONDITIONS
TO THE TERMINALS THROUGH 03Z TONIGHT. CONFIDENCE IN TIMING OF THE
CONVECTION WILL BE TRICKY...SO HAVE OPTED TO USE VCTS...WITH THE
EXCEPTION OF KTPA AND KPIE WHERE A HAVE INTRODUCED A TEMPOS DUE TO
THE CONVECTION ALREADY NOTED ON 88D RETURNS IN THE VICINITY OF THESE
TWO TERMINALS. OUTSIDE OF THE AFTERNOON CONVECTION AND AFTER 03Z
TONIGHT MAINLY VFR IS EXPECTED. WEST TO NORTHWEST WINDS IN THE 6 TO
8 KNOT RANGE CAN BE EXPECTED WITH GUSTS UP TO 40 KNOTS POSSIBLE IN
THE VICINITY OF TSRA. LIGHT AND VARIABLE WINDS WILL RETURN TO THE
TERMINALS AFTER 03Z TONIGHT.

&&

.MARINE...
HIGH PRESSURE CENTERED OVER THE NORTH CENTRAL GULF OF MEXICO WILL
KEEP WINDS OUT OF A NORTHWEST THROUGH NORTHEAST DIRECTION BELOW 15
KNOTS AND SEAS 1 TO 2 FEET THROUGH THE REMAINDER OF THE WEEKEND.
THUNDERSTORM CHANCES WILL ALSO REMAIN MINIMAL THROUGH SUNDAY WITH
LITTLE MORE THAN ISOLATED SHOWERS AND A FEW THUNDERSTORMS. WINDS
AND SEAS WILL INCREASE ON MONDAY AND TUESDAY AS THE GRADIENT
TIGHTENS BETWEEN THIS HIGH PRESSURE AND A TROPICAL DISTURBANCE
EAST OF THE BAHAMAS...POSSIBLY REACHING SMALL CRAFT EXERCISE
CAUTION CONDITIONS.

&&

.FIRE WEATHER...
AMPLE LOW LEVEL MOISTURE ALONG WITH DAILY RAIN CHANCES WILL KEEP
HUMIDITY VALUES ABOVE CRITICAL LEVELS THROUGH THE REMAINDER OF THE
WEEKEND AND INTO EARLY NEXT WEEK. A SLOW INCREASE IN 20 FOOT WINDS
AND TRANSPORT WINDS WILL SUPPORT ELEVATED DISPERSION INDICES ON
SUNDAY AND INTO EARLY NEXT WEEK.

&&

.PRELIMINARY POINT TEMPS/POPS...
TPA  81  95  79  93 /  30  50  30  40
FMY  78  95  78  93 /  30  30  20  50
GIF  77  96  76  91 /  20  50  20  50
SRQ  79  94  78  91 /  30  40  30  50
BKV  75  96  76  93 /  20  50  30  40
SPG  83  94  82  92 /  20  40  40  50

&&

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

$$

SHORT TERM/AVIATION/FIRE WEATHER...57/MCMICHAEL
LONG TERM...14/MROCZKA
MARINE...74/WYNN
DECISION SUPPORT...18/FLEMING





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