Area Forecast Discussion
Issued by NWS Tampa Bay Area, FL

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS62 KTBW 201927
AFDTBW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAMPA BAY RUSKIN FL
330 PM EDT MON OCT 20 2014

.SYNOPSIS...
19Z WATER VAPOR AND H4 RAP ANALYSIS SHOW A HIGHLY AMPLIFIED UPPER
LEVEL PATTERN IN PLACE ACROSS NORTH AMERICA. NORTHERN STREAM FLOW
ARRIVES OVER THE PACIFIC NORTHWEST/BRITISH COLUMBIA COAST AND
QUICKLY RIDGES WELL NORTH THROUGH THE CANADIAN ROCKIES. THE FLOW
THEN DIVES BACK TO THE SOUTH INTO THE UPPER MIDWEST/GREAT LAKES
REGION. A POTENT SHORTWAVE EMBEDDED WITHIN THIS FLOW DROPPING OUT OF
THE UPPER MIDWEST WILL ACT TO EVEN FURTHER AMPLIFY THE NORTHERN
STREAM AS IT CARVES OUT A DEEP TROUGH ALONG THE EASTERN SEABOARD BY
TUESDAY MORNING. THE FLOW IS CURRENTLY ZONAL IN NATURE OVER THE
NORTHERN GULF COAST/FLORIDA PENINSULA...BUT WILL BECOME MORE
CYCLONIC IN NATURE DURING THE NEXT 24 HOURS AS THE AMPLIFYING
EASTERN TROUGH TAKES FORM.

THE THE MORNING 20/12Z KTBW SOUNDING PROFILE SHOWED THE COLUMN IS
STILL VERY DRY. DEWPOINT DEPRESSIONS THROUGH A GOOD CHUNK OF THE
MID-LEVELS ARE RUNNING 35C...TO AS MUCH AS 50C...WHICH IS GOOD
REASON TO WHY THE CUMULUS FIELD IS SHALLOW TODAY. THE CALCULATED PW
VALUE WAS 0.69" WHICH IS GETTING DOWN TOWARD 2 STANDARD DEVIATIONS
BELOW CLIMATOLOGY FOR THE MIDDLE OF OCTOBER. SO...YA...ITS DRY.

AT THE SURFACE...OUR REGION CURRENTLY RESIDES IN A SYNOPTIC EASTERLY
FLOW BETWEEN A 1020MB RIDGE OF HIGH PRESSURE ALONG THE CAROLINA
COAST...AND A WEAK SURFACE TROUGH/LOW OVER THE WESTERN GULF OF
MEXICO/BAY OF CAMPECHE. THE PRESSURE GRADIENT HAS RELAXED SOMEWHAT
THROUGH THE DAY AS THE HIGH CENTER TO OUR NORTH DRIFTS FURTHER EAST
INTO THE ATLANTIC. THE WEAKENING GRADIENT COMBINED WITH STRONG
TERRESTRIAL HEATING HAS ALLOW A FEEBLE SEA-BREEZE CIRCULATION...WITH
MANY COASTAL WINDS NOW FLIPPING ONSHORE.

&&

.SHORT TERM (REST OF TODAY THROUGH TUESDAY)...
REST OF THIS AFTERNOON/EARLY EVENING...QUIET AND BENIGN FORECAST AND
TERMS OF SENSIBLE WEATHER. A DRY ATMOSPHERIC COLUMN AND VERY LITTLE
IN THE WAY OF SYNOPTIC SCALE LIFTING MECHANISMS KEEPING THE FORECAST
RAIN FREE. WITH PLENTY OF INSOLATION...TEMPERATURES HAVE MIXED OUT
TO THE LOWER/MIDDLE 80S FROM I-4 NORTHWARD AND MIDDLE/UPPER 80S
FURTHER SOUTH. THESE TEMPERATURES REPRESENT HIGHS A FEW DEGREES
"ABOVE NORMAL" FOR OCTOBER 20TH. SLIGHTLY COOLER TEMPERATURES WILL
BE SEEN AT THE IMMEDIATE COAST THE REMAINDER OF THE DAYLIGHT
HOURS...ESPECIALLY ALONG THE NATURE COAST WHERE NEARSHORE SATELLITE
DERIVED SST VALUES HAVE COOLED INTO THE UPPER 70S.

AS THE UPPER TROUGH DIGS OVER THE EASTERN GULF/FL PENINSULA TONIGHT
AND TUESDAY MORNING...WE WILL BEGIN TO SEE A SIGNIFICANT AND DEEP
LAYER SURGE OF MOISTURE RETURN UP INTO THE SOUTHERN HALF OF THE FL
PENINSULA. DURING THE DAY ON TUESDAY WITHIN THE BASE OF THE TROUGH
WILL BE WATCHING A DECENT UPPER LEVEL JET STREAK CROSSING THE
NORTHERN HALF OF THE STATE. THE RESULTING DIFFLUENT PATTERN ALOFT TO
THE SOUTH OF THIS FEATURE ALONG WITH A BROAD ZONE OF Q-VECTOR
CONVERGENT WILL BECOME COINCIDENT WITHIN THE REGION OF BEST MOISTURE
RETURN OVER THE SOUTHERN HALF OF THE PENINSULA TO SUPPORT SHOWER
CHANCES ACROSS OUR SOUTHERN ZONES BY MIDDAY TUESDAY (PERHAPS A BIT
EARLIER). NOW...JUST HOW FAR NORTH THE SHOWERS GET WILL BE
DETERMINED BY THE EXTENT OF MOISTURE RETURN...SINCE THE SYNOPTIC
LIFTING MECHANISMS WILL CERTAINLY EXIST OVER MUCH OF THE REGION.
HOWEVER...ENSEMBLE CONSENSUS CONTINUES TO SUGGEST THE BEST CHANCES
FOR ADEQUATE COLUMN MOISTURE SHOULD EXIST SOUTH OF A LINE FROM SAY
SARASOTA TO SEBRING...WITH HIGHEST RAIN CHANCES DOWN TOWARD FORT
MYERS AND SOUTHWARD. DID NOT MAKE ANY SIGNIFICANT ADJUSTMENTS FROM
THE INHERITED FORECAST THIS TIME AROUND...OTHER THAN TO RAISE POPS
ANOTHER 10% OR SO DOWN TOWARD CHARLOTTE/LEE COUNTIES. WENT BACK IN
FORTH WITH MENTIONING "LIKELY" RAIN CHANCES THIS FAR SOUTH...BUT
SOME UNCERTAINLY IN THE DEGREE OF MOISTURE RETURN KEPT RAIN CHANCES
CAPPED AT 50%. EVEN IF RAIN CHANCES NEED TO BE RAISED
FURTHER...ACCUMULATIONS STILL LOOK TO BE LIGHT AS NONE OF THE
LIFTING MECHANISMS ARE PARTICULARLY STRONG...JUST SIMPLY ADDITIVE
ENOUGH TO SUPPORT RETURNING SHOWERS TO THE FORECAST. ALONG AND NORTH
OF THE I-4 CORRIDOR...HAVE KEPT THE FORECAST RAIN FREE ONCE AGAIN AS
NO GUIDANCE MEMBER SUGGESTS THE MOISTURE WILL REACH THIS FAR NORTH.
THESE NORTHERN ZONES WILL ALSO SEE THE MOST SUNSHINE/INSOLATION AS
WELL...WITH A DEEPER/THICKER CLOUD CANOPY MOVING ASHORE ALONG THE
SUNCOAST.

&&

.LONG TERM (TUESDAY NIGHT-MONDAY)...
MEDIUM RANGE GUIDANCE IS COMING INTO BETTER AGREEMENT WITH RESPECT
TO THE SYNOPTIC PATTERN EVOLUTION THROUGH THE LONG TERM PERIODS.
THAT SAID...GIVEN THE RUN TO RUN CONTINUITY ISSUES AND LACK OF
A STRONG MODEL CONSENSUS OVER THE PAST COUPLE OF DAYS...CONFIDENCE
REMAINS BELOW AVERAGE PARTICULARLY IN THE LATTER PORTION OF THE LONG
TERM PERIOD.

MODEL SOLUTIONS ARE IN GOOD AGREEMENT SHOWING A DEEP UPPER LEVEL
TROUGH CLOSING OFF AN UPPER LOW OVER THE MID-ATLANTIC STATES TUESDAY
NIGHT AND WEDNESDAY...WITH THIS FEATURE THEN LIFTING INTO THE NEW
ENGLAND STATES BY FRIDAY EVENING. AS THIS OCCURS UPPER LEVEL
TROUGHING OVER THE FLORIDA PENINSULA TUESDAY NIGHT AND WEDNESDAY
WILL GIVE WAY TO WEAK UPPER LEVEL RIDGING THURSDAY THROUGH FRIDAY.
ANOTHER SHORTWAVE TROUGH WILL DIG INTO THE LOWER MISSISSIPPI VALLEY
AND NORTHERN GULF OF MEXICO ON FRIDAY...WITH THIS POSITIVE TILTED
UPPER TROUGH SHIFTING EAST-SOUTHEASTWARD AND INTO THE PENINSULA ON
SATURDAY AND INTO THE WESTERN ATLANTIC FOR SUNDAY AND MONDAY. THIS
SECONDARY SHORTWAVE TROUGH IS THE ONE THAT THE MODELS HAVE STRUGGLED
CAPTURING OVER THE PAST COUPLE OF DAYS...BUT THE 00Z GFS AND 00Z
ECMWF HAVE TRENDED VERY CLOSELY TOGETHER WITH THEIR HANDLING OF
THIS FEATURE...LEADING TO HIGHER ALBEIT STILL BELOW AVERAGE
CONFIDENCE.

AT THE SURFACE...A TROUGH OF LOW PRESSURE EXTENDING FROM BAY OF
CAMPECHE INTO THE FLORIDA STRAIGHTS WILL WILL MOVE VERY LITTLE
THROUGH FRIDAY EVENING. THE MAIN FEATURE THE MODELS ARE LATCHING
ONTO ALONG THIS TROUGH...IS THE BROAD AREA OF LOW PRESSURE OVER THE
BAY OF CAMPECHE WHICH WILL SHIFT SLOWLY EASTWARD INTO THE SOUTHEAST
GULF OF MEXICO AND NORTHWEST CARRIBEAN BY FRIDAY EVENING. THIS
FEATURE WILL THEN SHIFT EAST-NORTHEASTWARD THROUGH THE FLORIDA
STRAIGHTS INTO THE VICINITY OF THE BAHAMAS BY SATURDAY EVENING. HIGH
PRESSURE IS THEN EXPECTED TO SLOWLY BUILD FROM THE NORTH SATURDAY
NIGHT THROUGH EARLY NEXT WEEK.

AS FOR FORECAST DETAILS...WILL CONTINUE TO ADVERTISE SLIGHT
CHANCE/LOW CHANCE POPS IN THE FORECAST PRIMARILY SOUTH OF TAMPA BAY
TUESDAY NIGHT THROUGH SATURDAY. IT CERTAINLY DOESN/T APPEAR TO BE A
BIG RAIN MAKER FOR THIS PORTION OF THE STATE AS THE DEEPEST MOISTURE
WILL REMAIN ACROSS THE FLORIDA STRAIGHTS. BY SATURDAY NIGHT...THE
DEEPEST MOISTURE WILL HAVE SHIFTED OVER THE BAHAMAS IF THE 00Z
GFS/ECMWF SOLUTIONS HAVE TRENDED IN THE RIGHT DIRECTION...SO WILL
KEEP THE FORECAST OPTIMISTIC AND RAIN FREE FOR THE END OF THE
WEEKEND THROUGH EARLY NEXT WEEK.

&&

.AVIATION...
CONDITIONS ARE PREVAILING VFR ACROSS THE REGION THIS AFTERNOON UNDER
A FEW-SCT CUMULUS FIELD. ALTHOUGH A FEW SHOWERS ARE EXPECTED TUESDAY
MORNING AND EARLY AFTERNOON FROM KPGD SOUTH TO KFMY/KRSW..THE
REMAINDER OF THE TAF PERIOD WILL CONTINUE TO FEATURE GENERALLY VFR
CONDITIONS. WINDS DIRECTIONS WILL BECOME VARIABLE AT TIMES LATE THIS
AFTERNOON AS A WEAK SEA BREEZE DEVELOPS AND TRIES TO MIGRATE INLAND.
EXPECTING GENERALLY 10 KNOTS OR LESS THROUGH THE TAF PERIOD.

&&

.MARINE...
THE CURRENT MILD WEATHER WILL BE CHANGING OVER THE NEXT DAY OR TWO
AS LOW PRESSURE OVER THE SOUTH CENTRAL GULF WILL SHIFT TO THE
NORTHEAST AND BEGIN TO AFFECT SOUTH FLORIDA. CHANCES OF SHOWERS AND
THUNDERSTORMS WILL INCREASE FROM THE SOUTH ON TUESDAY AND NORTHEAST
WINDS WILL INCREASE TO THE 15 TO 20 KNOT RANGE STARTING THURSDAY AND
REMAIN THROUGH THE WEEKEND AS THE LOW PRESSURE MOVES THROUGH THE
FLORIDA STRAITS. WINDS AND SEAS HIGHER IN AND NEAR THUNDERSTORMS AND
WINDS MAY APPROACH SMALL CRAFT CRITERIA AT TIMES LATER THIS
WEEK.

&&

.FIRE WEATHER...
THE REGION WILL REMAIN IN A GENERALLY QUIET WEATHER PATTERN BETWEEN
LO PRESSURE DEVELOPING OFF THE MID-ATLANTIC STATES AND ANOTHER AREA
OF LOW PRESSURE OVER THE SOUTHWESTERN GULF OF MEXICO. A FEW SHOWERS
WILL RETURN TO THE FORECAST FOR ZONES MAINLY SOUTH OF THE I-4
CORRIDOR BY TUESDAY AFTERNOON...HOWEVER...RAINFALL ACCUMULATIONS ARE
ANTICIPATED TO BE LIGHT. RELATIVE HUMIDITY VALUES WILL REMAIN ABOVE
CRITICAL LEVELS THROUGH THE MIDDLE OF THE WEEK AND NO SIGNIFICANT
FIRE WEATHER CONCERNS ARE EXPECTED.

FOG POTENTIAL...SOME PATCHY GROUND FOG IS POSSIBLE TOWARD SUNRISE
THE NEXT TWO MORNING...HOWEVER NO SIGNIFICANT OR WIDESPREAD FOG IS
EXPECTED.

&&

.PRELIMINARY POINT TEMPS/POPS...
TPA  69  85  69  84 /   0  10  10  20
FMY  70  85  71  85 /  10  50  30  40
GIF  67  86  68  83 /   0  10  10  10
SRQ  67  84  68  85 /   0  20  20  20
BKV  59  86  59  84 /   0  10  10  10
SPG  72  84  72  84 /   0  10  10  20

&&

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

&&

$$

SYNOPSIS/SHORT TERM/AVIATION/FIRE WX...MROCZKA
LONG TERM...JELSEMA
MARINE...DOUGHERTY




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.