000
AXNT20 KNHC 212357
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL  
805 PM EDT THU APR 21 2011

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL 
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTION
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 2356 UTC. 

...THE ITCZ...

ITCZ AXIS IS ALONG 05N09W TO 00N21W TO 04S33W TO 00N50W.  
SCATTERED MODERATE TO STRONG CONVECTION WITHIN 210 NM N OF AXIS 
E OF 21W.  ISOLATED MODERATE CONVECTION WITHIN 120 NM EITHER 
SIDE OF AXIS W OF 32W. 

...DISCUSSION...

GULF OF MEXICO...
HIGH PRES OVER NE GULF MAINTAINS STEADY E TO SE FLOW ACROSS 
ENTIRE BASIN WITH WINDS W OF 92W SHIFTING S AND INCREASING.
DRY AND STABLE SUBSIDING AIR MASS PRODUCING FAIR SKIES OVER  
ENTIRE GULF. 

IN THE UPPER LEVELS...NW FLOW PREVAILS SUPPORTING SURFACE HIGH 
PRES WHILE MOISTURE IS KEPT INLAND OVER SE COASTAL STATES. 
OTHERWISE EXPECT LITTLE CHANGE OVER THE NEXT 24 HOURS.  

CARIBBEAN SEA...
FRESH TRADEWINDS ACROSS CARIBBEAN SEA CONVERGING WITH STRONG 
NORTHEASTERLIES CROSSING GREATER ANTILLES FROM WESTERN ATLANTIC 
OCEAN INCREASING MOISTURE AND UPLIFTING OVER ISLANDS.  MODERATE 
SWELLS OVER NORTHERN SHORES BOUND TO GET HIGHER OVER THE WEEKEND 
AS LOW PRES OVER ATLANTIC CONTINUES GENERATING HIGH SEAS.  
SCATTERED SHOWERS ACROSS GREATER ANTILLES ENHANCED BY ABUNDANT 
MOISTURE AND DAYTIME HEATING.  ALSO OVER CENTRAL AMERICA FROM 
PANAMA TO GUATEMALA.  

IN THE UPPER LEVELS...WEAK RIDGE OVER NORTHERN SOUTH AMERICA 
MAINTAINS MODERATE SUBSIDENCE OVER SOUTHERN HALF OF CARIBBEAN 
SEA.  

ATLANTIC OCEAN...
MAIN FEATURE OVER ATLANTIC IS A HEALTHY LOW PRES 1009 MB CENTER 
AT 25N63W EMBEDDED IN TROUGH WHICH EXTEND FROM 27N61W TO 22N65W. 
BOTH ARE DRIFTING N-NW WITH STRONG WINDS OVER LOW PRES CENTER N 
SEMICIRCLE.  LOW PRES EXPECTED TO HOLD INTENSITY AND MEANDER SW 
THROUGH LATE FRI THEN WEAKEN AND BECOME DIFFUSE BY THE WEEKEND.
SCATTERED MODERATE TO STRONG CONVECTION NOTED OVER N SEMICIRCLE 
WITH ISOLATED TSTMS S OVER S SEMICIRCLE.  ELSEWHERE...A 1030 MB 
HIGH PRES OVER CENTRAL ATLANTIC NEAR 35N41W MAINTAINS FAIR AND 
STABLE AIR MASS W OF 50W.

IN THE UPPER LEVELS...DEEP LAYER CYCLONIC CIRCULATION SUPPORTS 
SURFACE LOW PRES MENTIONED ABOVE.  SUBTROPICAL JETSTREAM WITH 90 
KT MAINTAINING STRONG SHEAR OVER LOW PRES WEAKENS ALLOWING ITS 
STEADY STRENGTH.    

FOR ADDITIONAL INFORMATION PLEASE VISIT
HTTP://WWW.HURRICANES.GOV/MARINE

$$
WALLY BARNES