Area Forecast Discussion
Issued by NWS Tampa Bay Area, FL

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FXUS62 KTBW 201246
AFDTBW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAMPA BAY RUSKIN FL
845 AM EDT MON OCT 20 2014

.UPDATE (REST OF TODAY THROUGH TUESDAY)...
13Z 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
THIS TIME TOMORROW. THE FLOW IS CURRENTLY MORE 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.

TAKING A PEAK AT THE MORNING 20/12Z KTBW SOUNDING PROFILE...THE
COLUMN IS STILL VERY DRY. FAIRLY OBVIOUS WHY OUR SKIES ARE MOSTLY
CLEAR THIS MORNING. DEWPOINT DEPRESSIONS THROUGH A GOOD CHUNK OF THE
MID-LEVELS ARE RUNNING 35C...TO AS MUCH AS 50C. 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. ONE CAN MAKE AN ARGUMENT FOR A SUBTLE
BOUNDARY FEATURE/WARM FRONT SOMEWHERE NEAR OR JUST NORTH OF THE I-4
CORRIDOR. THIS BOUNDARY REALLY IS JUST A SURFACE DEWPOINT
GRADIENT...AND SHOULD TEND TO WASH OUT THROUGH THE DAY. THE PRESSURE
GRADIENT ALSO LOOKS AS THOUGH IT WILL RELAX SOMEWHAT THROUGH TODAY
AS THE LOW REMAIN IN PLACE...AND THE HIGH CENTER DRIFTS FURTHER EAST
INTO THE ATLANTIC. THE WEAKENING GRADIENT SHOULD ALLOW AT LEAST A
FEEBLE SEA-BREEZE CIRCULATION TO DEVELOP IN THE AFTERNOON AND TURN
OUR WINDS ONSHORE AT THE BEACHES.

REST OF TODAY...ANOTHER QUIET AND BENIGN FORECAST AND TERMS OF
SENSIBLE WEATHER. A DRY ATMOSPHERIC COLUMN AND VERY LITTLE IN THE
WAY OF SYNOPTIC SCALE LIFTING MECHANISMS WILL KEEP THE FORECAST RAIN
FREE. WITH PLENTY OF INSOLATION THROUGH THE DAY...AFTERNOON
TEMPERATURES SHOULD MIX 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.
LIKELY TO SEE SLIGHTLY COOLER TEMPERATURES AT THE IMMEDIATE COAST
ONCE THE WIND SHIFTS ONSHORE...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 TUESDAY AFTERNOON. 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 WOULD 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. INHERITED FORECAST HAS CHANCE 30-40% POPS FOR THESE FAR
SOUTHERN ZONES TUESDAY AFTERNOON. WILL EVALUATE THE 12Z GUIDANCE FOR
THE NEXT FORECAST PACKAGE...BUT IF THE GUIDANCE DOES NOT DEVIATE
MUCH WITH THIS NEXT RUN...RAIN CHANCES MAY NEED TO BE RAISED A BIT
DOWN SOUTH. EVEN IF RAIN CHANCES ARE RAISED...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.

&&

.AVIATION...
CONDITIONS ARE PREVAILING VFR ACROSS THE REGION THIS MORNING. WAS A
BIT OF PATCHY FOG AROUND SUNRISE...BUT THESE PATCHES ARE QUICKLY
LIFTING WITH THE ONSET OF DIURNAL HEATING. THE REST OF THE TAF
PERIOD WILL CONTINUE TO FEATURE VFR CONDITIONS. WINDS DIRECTIONS
WILL BECOME VARIABLE AT TIMES LATER THIS AFTERNOON AS A WEAK SEA
BREEZE DEVELOPS AND TRIES TO MIGRATE INLAND. EXPECTING GENERALLY 10
KNOTS OR LESS THROUGH THE TAF PERIOD.

&&

.MARINE...
SOUTHEAST WINDS LESS THAN 15 KNOTS WILL CONTINUE THROUGH THE
DAY...EXCEPT FOR ALONG THE COASTLINE WHERE A SEA BREEZE WILL SET UP
LATER THIS AFTERNOON. THE WINDS WILL THEN DECREASE THIS EVENING
BECOMING LIGHT AND VARIABLE OVERNIGHT. WITH THE LIGHTER WINDS...SEAS
ARE EXPECTED TO REMAIN LESS THAN 2 FEET UNTIL MID WEEK WHEN THE
GRADIENT TIGHTENS BETWEEN HIGH PRESSURE TO THE NORTH AND A LOW
PRESSURE CENTER MOVING THROUGH THE FLORIDA STRAITS. WINDS WILL BE
OUT OF A NORTHEAST DIRECTION AND MAY INCREASE TO NEAR SMALL CRAFT
CRITERIA...DEPENDING ON THE EVOLUTION OF THE LOW PRESSURE SYSTEM TO
OUR SOUTH THROUGH THE MIDDLE AND LATER PORTION OF THE WEEK. THE
FORECAST WILL REMAIN DRY THROUGH TODAY BUT RAIN CHANCES INCREASE FOR
THE SOUTHERN WATERS STARTING TONIGHT AND CONTINUING THROUGH THE END
OF THE WEEK.

&&

.PRELIMINARY POINT TEMPS/POPS...
TPA  86  70  85  69 /   0   0  10  10
FMY  88  70  84  71 /   0  10  40  30
GIF  86  69  85  68 /   0   0  20  10
SRQ  85  67  83  68 /   0  10  20  20
BKV  87  59  85  59 /   0   0  10  10
SPG  85  72  84  72 /   0   0  10  10

&&

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

&&

$$

UPDATE/AVIATION...MROCZKA
MARINE...WYNN





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