[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 302357
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 PM EST SUN NOV 30 2008

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS
OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST
FROM THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED
ON SATELLITE IMAGERY...METEOROLOGICAL ANALYSIS...WEATHER
OBSERVATIONS...AND RADAR.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY
THROUGH 2315 UTC.

...THE ITCZ...
FROM GUINEA/SIERRA LEONE IN AFRICA NEAR 10N12W TO 5N30W 4N40W
INTO NORTHEASTERN BRAZIL NEAR 02N51W. SCATTERED MODERATE
CONVECTION EXISTS WITHIN 270 NM S OF AXIS BETWEEN 19W AND 34W
AND WITHIN 90 NM N OF AXIS BETWEEN 26W AND 36W.


...DISCUSSION...

THE GULF OF MEXICO...
A VIGOROUS...DEEP-LAYERED TROUGH EXTENDS FROM THE EAST CENTRAL
CONUS INTO THE GULF OF MEXICO...CARRYING WITH IT AN ASSOCIATED
STRONG COLD FRONT FROM JUST E OF TALLAHASSEE THROUGH 26N86W TO
THE N CENTRAL YUCATAN. THE FRONT THEN CONTINUES SW TO W THROUGH
THE NORTHERN ISTHMUS OF TEHUANTEPEC AND A LARGE PART OF NORTHERN
MEXICO. STRONG DYNAMICS ASSOCIATED WITH A STRONG 150 KT JET
STREAK ROTATING THROUGH THE TROUGH OVER THE SOUTHEASTERN STATES
HAVE HELPED PRODUCE A NEARLY SOLID LINE OF CONVECTION JUST
AHEAD OF THE MAIN COLD FRONT. ON TOP OF THE CONVECTION SHIPS
...BUOYS...AND C-MAN STATIONS OVER THE EASTERN GULF ARE
REPORTING SOUTHERLY 20 TO SOMETIMES 30 KT WINDS WITH GUSTS
POSSIBLY TO GALE FORCE IN RAPIDLY BUILDING SEAS.

STRONG SOUTHERLY SURFACE WINDS ADVECTING LOW-LEVEL MOISTURE AND
INSTABILITY NORTHWARD AHEAD OF THE COLD FRONT SHOULD CONTINUE TO
CREATE AN ENVIRONMENT FAVORABLE FOR SEVERE WEATHER OVER THE
SOUTHERN HALF OF FLORIDA AND THE SE GULF OF MEXICO EARLY
TONIGHT. MOREOVER...AN IMPRESSIVE LAYER OF DEEP SHEAR ASSOCIATED
WITH PARTICULARLY STRONG SOUTHWESTERLY FLOW ALOFT WILL ENHANCE
THE POTENTIAL FOR SEVERE THUNDERSTORMS OVER THIS AREA. FOR
THIS REASON...THE STORM PREDICTION CENTER HAS ISSUED A TORNADO
WATCH FOR PORTIONS OF S FLORIDA AND THE ADJACENT COASTAL WATERS
THROUGH AT LEAST THROUGH THIS EVENING.  SURFACE OBSERVATIONS AND
DOPPLER RADAR ALREADY INDICATE A BROKEN SQUALL LINE...WHICH
HAS FORMED ALONG A PRE-FRONTAL TROUGH RUNNING FROM 31N80W TO
JUST SE OF FT MYERS AS OF 2100 UTC. THE SQUALL LINE IS ADVANCING
RAPIDLY SOUTHEASTWARD TOWARD SE FLORIDA AND THE KEYS.

BEHIND THE FRONT...LOW-LEVEL DIVERGENCE HAS GIVEN WAY TO
CLEARING SKIES...WITH RAPID PRESSURE RISES LEADING TO A NW TO N
20 TO 25 KT FLOW. SURFACE DATA ALSO SUGGESTS THAT A SECONDARY
COLD FRONT HAS SURGED INTO THE FAR NW WATERS ALONG A LINE FROM
NEAR LAFAYETTE LA TO NEAR CORPUS CHRISTI TX. PER MODEL
GUIDANCE...WINDS SHOULD FURTHER INCREASE BEHIND THIS SECONDARY
BOUNDARY...WITH W TO NW WINDS OF 20 TO 30 KT ON AVERAGE. THERE
IS ALSO A GOOD CHANCE OF GALE FORCE WINDS FOR A BRIEF TIME OVER
THE N CENTRAL AND NE OFFSHORE WATERS BEGINNING LATER TONIGHT
INTO EARLY MON MORNING.

THE CARIBBEAN SEA...
SATELLITE PICTURES AND AND EARLIER ASCAT PASS REVEALS THAT A
WEAK SURFACE LOW JUST N OF PANAMA YESTERDAY HAS TRACKED WNW TO
NW OVER THE LAST 24 HOURS. LATEST OBSERVATIONS SUGGEST THAT THE
1010 MB LOW IS NOW ROUGHLY NEAR 12N82W MOVING JUST W OF DUE N
AROUND 10 KT. LOW-LEVEL CONVERGENCE NEAR THIS SURFACE LOW IS
SUPPORTING SCATTERED SHOWERS AND THUNDERSTORMS S OF 12N W OVER
PANAMA...COSTA RICA....NICARAGUA AND THE ADJACENT CARIBBEAN
WATERS. ADDITIONAL THUNDERSTORMS HAVE DEVELOPED ALONG A LOW
-LEVEL CONFLUENT AXIS...A DEMARCATION BETWEEN THE EASTERN TRADES
AND SOUTHERLY FLOW SE OF THE SURFACE LOW. ALL OF THIS ACTIVITY
IS BEING ENHANCED BY UPPER LEVEL DIFFLUENCE IN THE VICINITY OF
AN UPPER RIDGE PRESENT OVER THE W CARIBBEAN...WITH THE AXIS OF
THIS UPPER RIDGE EXTENDING FROM CENTRAL COLOMBIA NEAR 07N75W TO
CENTRAL NICARAGUA.

OVER THE EASTERN HALF OF THE CARIBBEAN...DEEP LAYER SUBSIDENCE
AND DEEP LAYER DRY AIR ARE IN PLACE RESULTING IN FAIR WEATHER
...WHERE NORTHWESTERLY FLOW ALOFT IS PRESENT. IN ADDITION...
ENHANCED SURFACE RIDGING FROM THE CENTRAL ATLANTIC INTO THE
CENTRAL CARIBBEAN IS RESULTING IN INCREASED TRADES MOSTLY E OF
70W.

ELSEWHERE...SOUTHERLY FLOW OVER THE NW CARIBBEAN HAS BEEN
INCREASING THROUGHOUT THE DAY. IN FACT...AN EARLIER ASCAT PASS
OVER THE REGION SUGGESTED A BROAD AREA OF 20 TO 25 KT WINDS...
WITH THE STRONGEST WINDS MOSTLY N OF 18N W OF 82W.  MODELS
FORECAST THE SURFACE COLD FRONT CURRENTLY OVER THE GULF OF
MEXICO TO REACH THE YUCATAN CHANNEL AND THEN THE FAR NW
CARIBBEAN EARLY MON MORNING. FOLLOWING ITS PASSAGE...STRONG
NORTHERLY FLOW OF 20 TO 30 KT SHOULD DEVELOP IN THE NW CARIBBEAN
...WITH THE FRONT SETTLING ALONG AN AXIS FROM SE CUBA THROUGH
15N81W TO NORTHERN COSTA RICA BY TUE EVENING.

THE ATLANTIC OCEAN...
THE DEEP-LAYERED TROUGH MENTIONED ABOVE OVER THE EAST CENTRAL
CONUS HAS ALREADY BEGUN TO IMPACT THE SOUTHWEST NORTH ATLANTIC
WATERS. THE PRESSURE GRADIENT BETWEEN ENHANCED LOW-LEVEL
SUBTROPICAL RIDGING NEAR 28N56W AND DEEPENING LOW PRESSURE OVER
THE CAROLINAS HAS RESULTED IN A SOUTHERLY GALE N OF 27N W OF
72W. CONFIRMING THIS IS BUOY 41010 NEAR 29N78.5W...WHICH HAS
BEEN REPORTING NEAR CONTINUOUS GALE FORCE WINDS AND SEAS UP TO
17 FT DURING THE LAST FEW HOURS. S TO SW WINDS OF 30 TO 40 KT
SHOULD CONTINUE N OF 27N W OF 72W FOR AT LEAST THE NEXT 6 TO
PERHAPS 12 HOURS AND THEN BEGINNING TO DIE DOWN A BIT BY MON
AFTERNOON.

BETWEEN NOW AND THEN THE STRONG SURFACE COLD FRONT SWEEPING
ACROSS THE GULF WILL PUSH INTO THE SOUTHWEST NORTH ATLANTIC
...ACCOMPANIED BY A LINE OF STRONG TO SEVERE THUNDERSTORMS.
STRONG THUNDERSTORMS HAVE ALREADY DEVELOPED ALONG A FAST-MOVING
SQUALL LINE... EXTENDING FROM 31N80W TO SOUTHEAST FLORIDA. LARGE-
SCALE CONDITIONS OF STRONG UPPER-LEVEL DIVERGENCE...IMPRESSIVE
MOISTURE ADVECTION AND INCREASING INSTABILITY...AS WELL AS
DEEP-LAYERED SHEAR ARE ALL LIKELY TO CONTRIBUTE TO ADDITIONAL
STRONG TO POSSIBLY SEVERE THUNDERSTORMS OVER THE FLORIDA
PENINSULA AND ADJACENT WATERS INTO TONIGHT. AT PRESENT...A
TORNADO WATCH IN EFFECT FOR PORTIONS OF  FLORIDA AND THE
ADJACENT COASTAL WATERS UNTIL 8 PM EST THIS EVENING.

OTHERWISE...THE ENHANCED SUBTROPICAL RIDGE MENTIONED ABOVE NEAR
28N56W IS RESPONSIBLE FOR A BROAD ZONE OF INCREASED TRADES OVER
THE TROPICAL NORTH ATLANTIC...GENERALLY FROM 10N TO 23N BETWEEN
45W AND 65W. THESE WINDS ARE EXPECTED TO PERSIST FOR THE NEXT
DAY OR TWO...RESULTING IN SEAS BUILDING TO 7 TO 11 FT E OF THE
LESSER ANTILLES IN NE SWELL.

FINALLY...A BROAD...COMPLEX AREA OF LOW PRESSURE IS BEGINNING TO
FORM N OF THE AREA ALONG 35W IN ASSOCIATION WITH A MID- TO
UPPER-LEVEL TROUGH OVER THE NORTHEAST ATLANTIC IN THE PROCESS OF
CUTTING OFF. WITHIN THE NEXT FEW DAYS...THE ASSOCIATED SURFACE
LOW PRESSURE SHOULD DIP INTO THE FORECAST WATERS AND BEGIN
TRACKING WESTWARD UNDERNEATH BLOCKING HIGH PRESSURE TO THE
NORTH. MODERATE TO STRONG NORTHEASTERLY FLOW IS EXPECTED TO FORM
BETWEEN IT AND THE ENHANCED SURFACE RIDGE TO THE WEST
...ULTIMATELY LEADING TO BUILDING SEAS IN NE SWELL.

OF NOTE...NOVEMBER 30 MARKS THE CONCLUSION OF THE 2008 ATLANTIC
HURRICANE SEASON. DURING THIS SEASON...SIXTEEN NAMED TROPICAL
CYCLONES OCCURRED. OF THESE SIXTEEN...EIGHT WERE HURRICANES...OF
WHICH FIVE WERE MAJOR HURRICANES OF SAFFIR-SIMPSON CATEGORY
THREE STRENGTH OF STRONGER. THIS SEASON WAS THE FIRST EVER WHEN
SIX CONSECUTIVE TROPICAL CYCLONES MADE LANDFALL ON THE CONUS
MAINLAND. OVERALL...THE 2008 HURRICANE SEASON IS TIED AS THE
FOURTH MOST ACTIVE IN TERMS OF NUMBER OF NAMED STORMS AND MAJOR
HURRICANES...AND IS ALSO TIED AS FIFTH MOST ACTIVE IN TERMS OF
NUMBER OF HURRICANES SINCE 1944...THE BEGINNING OF THE AERIAL
RECONNAISSANCE ERA. FINALLY...THIS IS THE TENTH SEASON TO
PRODUCE ABOVE-NORMAL TROPICAL CYCLONE ACTIVITY SINCE 1995 WHEN
THE CURRENT ACTIVE HURRICANE ERA BEGAN. ADDITIONALLY...A TOTAL
OF 64 TROPICAL WAVES MOVED OFF THE COAST OF AFRICA THIS SEASON
WHICH IS NEAR THE SEASONAL AVERAGE.



$$
KIMBERLAIN/COHEN/RUBIO





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