000
AXNT20 KNHC 201746
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT THU MAR 20 2008

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL 
AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHERN 
SECTIONS OF SOUTH AMERICA...AND THE 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1745 UTC.

...THE ITCZ...

FROM THE LIBERIA COAST NEAR 6N10W TO 2N20W CROSSING THE EQUATOR 
AT 30W TO 1.5S44W 1N30W. ISOLATED TO SCATTERED MODERATE 
CONVECTION FROM 5S TO 3N BETWEEN 2W AND 20W.

...DISCUSSION...

THE GULF OF MEXICO...
A SHORTWAVE TROUGH NEARING 80W OVER THE ERN CONUS IS PUSHING AN 
ASSOCIATED COLD FRONT DOWN THE FLORIDA PENINSULA AND THROUGH THE 
SERN GULF OF MEXICO/YUCATAN...EXTENDING FROM NEAR NAPLES FL TO 
22N88W AND THEN SOUTHWARD TO 15N91W AT 1500 UTC.  VISIBLE 
SATELLITE IMAGERY REVEALS A BROAD BAND OF LOW- TO MID-LEVEL 
CLOUDS NEAR AND WITHIN ABOUT 150 NM WEST OF THE BOUNDARY 
...THOUGH WITH LITTLE TO NO DEEP CONVECTION. HOWEVER...THE 
COMBINATION OF 1.5 TO 1.75 PRECIPITABLE WATER VALUES...DYNAMICS 
ASSOCIATED WITH THE TAIL OF A 90-130 KT NE-SW JET EXTENDING 
INTO THE NERN GULF OF MEXICO...AND SUFFICIENT LIFT ALONG THE 
FRONT COULD STILL IGNITE SCATTERED SHOWERS AND TSTMS NEAR AND 
AHEAD OF THE BOUNDARY LATER THIS AFTERNOON AND EVENING. IN 
ADDITION
...A MORNING QUIKSCAT PASS INDICATED A MOSTLY N-NE LOW-LEVEL 
FLOW OF 15-20 KT WEST OF 90W AND N OF THE FRONT...WITH SOME 
OCCASIONAL 25 KT WINDS POSSIBLE CLOSE TO THE MOUTH OF THE MS 
RIVER. SPOTTY SHIP REPORTS AND BUOY OBSERVATIONS SUGGEST A 
SIMILAR NLY FLOW E OF 90W AND DIRECTLY BEHIND THE FRONT...WITH 
WINDS LIKELY TO VEER MORE N TO NE BY LATE TODAY.  AS A RESULT OF 
THE GALE FORCE WINDS FROM YESTERDAY...SEAS ARE STILL AROUND 6 TO 
10 FT IN NLY SWELL WEST OF 85W EXCEPT OFFSHORE THE TX COAST. 
BEHIND THE FRONT OVER THE ISTHMUS OF TEHUANTEPEC...A SLIGHTLY 
LATER QUIKSCAT PASS REVEALED 45 KT WINDS JUST SOUTH OF THE GULF 
OF TEHUANTEPEC...WITH WINDS LIKELY TO DIMINISH BELOW GALE FORCE 
BY FRI AFTERNOON.


AS THE ERN CONUS SHORTWAVE HEADS EAST TONIGHT AND FAILS TO DIG 
APPRECIABLY...EXPECT THE COLD FRONT TO CLEAR THE FLORIDA 
PENINSULA AND BECOME STATIONARY FROM THE FL STRAITS TO NORTH OF 
THE YUCATAN FRI MORNING...WITH A 1028MB SURFACE RIDGE BEHIND IT 
OVER THE CAROLINAS.  THIS PATTERN SHOULD FAVOR A BRISK ELY FLOW 
E OF 90W MUCH OF FRI...WHICH SHOULD KEEP ALL BUT THE NW GULF 
WITH 5 TO 8 FT SEAS IN NE TO E SWELL.  LATER FRI...WEAK 
SHORTWAVE ENERGY PASSING THROUGH THE DEEP SOUTH AND GULF OF 
MEXICO SHOULD ACTIVATE A WEAK SURFACE WAVE ALONG THE STATIONARY 
BOUNDARY OVER THE SOUTH CENTRAL GULF...WHICH SHOULD TRACK 
RAPIDLY ENE ACROSS CENTRAL FL SAT. SOON THEREAFTER...AN EVEN 
STRONGER NRN STREAM DISTURBANCE SHOULD DRIVE A STRONGER FRONT 
OFF THE SERN CONUS COAST SUN MORNING...WITH STRONG HIGH PRESSURE 
BUILDING INTO THE GULF BEHIND BOTH SYSTEMS.  

CARIBBEAN SEA...

THE TAIL OF A COLD FRONT ASSOCIATED WITH WHAT ONCE WAS A STRONG 
STORM CENTER OVER THE WESTERN ATLANTIC EARLIER THIS WEEK HAS 
PUSHED WELL INTO THE EASTERN CARIBBEAN AND LESSER ANTILLES AS OF 
THIS MORNING.  VISIBLE SATELLITE IMAGERY SHOWS PATCHES OF 
STRATOCUMULUS CLOUDS HAVING PENETRATED FROM ANTIGUA THROUGH 
PUERTO RICO...THOUGH THEIR COVERAGE HAS DIMINISHED CONSIDERABLY 
SINCE 1200 UTC. UPPER-AIR DATA FROM SAN JUAN ALSO INDICATES A 
RECOVERY TO THE NORMAL TRADE WIND INVERSION ACROSS THE 
REGION...THOUGH THE INVERSION LEVEL OF 750 MB IS STILL LIKELY 
MUCH HIGHER-THAN-AVERAGE. IN ADDITION...SURFACE OBS ACROSS THE 
REGION INDICATE DEWPOINTS FROM THE UPPER 50'S TO MID 60'S OVER 
THE NE CARIBBEAN NORTH OF THE DIFFUSE BOUNDARY...WITH 
TEMPERATURES STILL SEVERAL DEGREES COOLER THAN CLIMATOLOGICAL 
AVERAGES.

ELSEWHERE...STRONG HIGH PRESSURE BEHIND THE FRONT HAS LOST MUCH 
OF ITS VIGOR THE LAST TWO DAYS...AND THUS THE TRADE WIND FLOW 
OVER TH ERN AND CENTRAL CARIBBEAN HAS DRASTICALLY DIMINISHED.  
HOWEVER...A 1038 UTC QUIKSCAT PASS DID SHOW A HEALTHY AREA OF 
20 TO 25 KT WINDS BETWEEN 70W AND 78W...WITH SEVERAL INDICATIONS 
OF 30 KT WINDS DIRECTLY OFFSHORE THE COAST OF COLOMBIA.  SEAS 
CONTINUE TO REMAIN 6 TO 12 FT IN MOSTLY NE TO E SWELL.  HOWEVER 
...LARGE LONG PERIOD SWELL ORIGINATING FROM THE EARLY WEEK 
STORM OVER THE WRN ATLANTIC CONTINUES TO PROPAGATE THROUGH THE 
ATLANTIC PASSAGES...CREATING SEAS OF 12 TO 17 FT THROUGH PUERTO 
RICO AND PARTS OF THE NORTHERN ANTILLES.  OTHERWISE...SEVERAL 
STREAMERS OF CLOUDS AND SHOWERS ARE FORMING DOWNWIND OF THE 
LARGE ISLANDS IN THE ANTILLES CHAIN...WITH A MORE PROMINENT 
BROKEN BAND EXTENDING ALONG 17N63W 16N68W 16N73W.

FINALLY...AN ANOMALOUSLY STRONG MID- TO UPPER-LEVEL ANTICYCLONE 
COVERS MUCH OF THE BASIN TODAY WITH A CONTINUATION OF STRONG 
SUBSIDENCE SEEN IN WATER VAPOR IMAGERY ALL AREAS E OF 85W.  AS A 
RESULT OF THE UNUSUALLY STRONG RIDGE ALOFT...DEEP EASTERLY FLOW 
AT UPPER-LEVELS COVER MUCH OF SOUTH AMERICA INTO THE ERN 
PACIFIC...AN UNUSUAL SIGHT FOR THE THIRD WEEK OF MARCH. OVER THE 
NEXT FEW DAYS...MODEL GUIDANCE INDICATES THAT THIS RIDGE SHOULD 
BEGIN TO SHIFT FARTHER EAST...AS HEIGHTS FALL OVER THE GULF OF 
MEXICO AND ERN CONUS COAST LATE THIS WEEKEND.

ATLANTIC...
THE SAME COLD FRONT PUSHING THROUGH THE SERN GULF OF MEXICO THIS 
MORNING IS ALSO MAKING SEWD PROGRESS OVER THE SW ATLC... 
EXTENDING ALONG 31N77W TO AROUND VERO BEACH FL AT 1500 UTC. AN 
EARLIER QUIKSCAT PASS SHOWED A BROAD AREA OF SWLY 25- TO 30-KT 
WINDS WITHIN ABOUT 400 NM EAST OF THE FRONT NORTH OF 28...WHICH 
IS GENERATING 10 TO 13 FT SEAS IN MIXED NE AND SW SWELL AHEAD OF 
THE FRONT.  SATELLITE IMAGERY ALSO INDICATES A THIN LINE OF 
BROKEN SHOWERS AND TSTMS FORMING WITHIN ABOUT 60 NM EAST OF THE 
FRONT FROM ACROSS SOUTH FLORIDA WITH A MORE CONCENTRATED LINE 
FARTHER NE.  EXPECT THE FRONT TO CONTINUE SWD TODAY...SETTLING 
INTO NORTH CENTRAL BAHAMAS AND STALLING OUT BY LATE FRI...WITH A 
1025MB SFC RIDGE MOVING OFFSHORE THE SE CONUS COAST.

LONG PERIOD N TO NE SWELL CONTINUES TO DOMINATE MUCH OF THE 
ATLANTIC BASIN SOUTH OF 31N...REMNANT FROM THE STORM SYSTEM 
WHICH AFFECTED THE WRN ATLANTIC EARLY THIS WEEK.  SHIP REPORTS 
AND BUOY OBSERVATIONS CONTINUE TO SHOW 10 TO 15 FT SEAS IN NE 
SWELL WEST OF 65W...WITH 16 TO 22 FT SEAS IN NW TO N SWELL NORTH 
OF 20N AND EAST OF 60W. THE SWELL HAS PROPAGATED DEEP INTO THE 
TROPICAL ATLANTIC...STRAIGHT TO THE SOUTH AMERICAN COAST AND 
SHOULD CONTINUE DOING SO THROUGH THE WEEKEND...WITH SEAS 
GRADUALLY SUBSIDING FROM NW TO SE.

ELSEWHERE...A LARGE CLOSED CYCLONE NEAR 36N49W REMAINS NEARLY 
STATIONARY...BLOCKED BY AN ENORMOUS BLOCKING HIGH OVER THE FAR 
NORTH ATLANTIC SOUTH OF GREENLAND.  AN ASSOCIATED COLD FRONT 
EXTENDS ALONG 31N41W TO 15N51W AND IS SLOWLY PRESSING SEWD.
AS THE BLOCK WEAKENS THE NEXT FEW DAYS...EXPECT THE CLOSED 
CYCLONE TO GRADUALLY HEAD EWD ALONG WITH THE COLD WHICH SHOULD 
PUSH EAST OF THE AREA BY EARLY SAT MORNING.

OTHERWISE...A FLAT ANTICYCLONE AT MID- TO UPPER-LEVELS COVERS 
THE TROPICAL ATLANTIC...WITH AN AXIS ALONG 15N.  ANOMALOUS ELY 
FLOW CONTINUES SOUTH OF 10N FROM THE LESSER ANTILLES EWD TO THE 
COAST OF AFRICA.


$$
KIMBERLAIN