000
AXNT20 KNHC 282356
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT TUE APR 28 2009

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
2345 UTC.

...THE ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 05N84W TO THE EQUATOR AT 20W TO 
05S35W. SCATTERED MODERATE AND ISOLATED STRONG CONVECTION IS 
OBSERVED WITHIN 120 NM OF 03N15W.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER LEVEL TROUGH IS OVER THE CENTRAL GULF PROGRESSING 
EASTWARD WITH TIME AND NOW HAS A LOW LEVEL REFLECTION FROM THE 
YUCATAN PENINSULA TO TO 26N86W. THE UPPER DIFFLUENCE ENHANCED A 
VERY SMALL AREA OF SHOWERS OVER THE FLORIDA STRAITS BETWEEN THE 
DRY TORTUGAS AND NW CUBA LATE THIS AFTERNOON...BUT THE AREA HAS 
ALMOST COMPLETELY DISSIPATED. ANOTHER AREA OF SHOWERS HAS 
DEVELOPED FROM THE EASTERN YUCATAN CHANNEL TO TO 26N87W AND 
SEEMS TO BE MOVING W IN THE LOW LEVEL FLOW. SOME UPPER DEBRIS 
CIRRUS FROM CONVECTION OVER INTERIOR E TEXAS IS STREAMING S OVER 
THE NORTHERN GULF...GENERALLY NW OF A LINE FROM 24N94W TO 29N84W.
OTHERWISE THE UPPER LEVELS APPEAR QUITE DRY. ELSEWHERE AT THE 
SURFACE...HIGH PRES LOCATED OVER THE W ATLC NEAR 33N75W HAS A 
RIDGE EXTENDING W ACROSS N FLORIDA AND DISSECTING THE GULF OF 
MEXICO FROM NW FLORIDA TO SE TEXAS. THE ASSOCIATED GRADIENT IS 
MAINTAINING FRESH E TO SE LOW LEVEL FLOW ACROSS GULF WATERS.

CARIBBEAN SEA...
AN QUASI STATIONARY UPPER LEVEL ANTICYCLONE OVER S AMERICA IS 
CURRENTLY ESTIMATED NEAR 05N60W. AN ASSOCIATED UPPER RIDGE 
EXTENDS NW ACROSS COLOMBIA TO NEAR BELIZE. UPPER DEBRIS MOISTURE 
FROM CONVECTION FLARING ALONG THE E PACIFIC ITCZ...AND SOME 
INTENSE LATE AFTERNOON CONVECTION OVER CENTRAL AMERICA...IS 
STREAMING NE ACROSS THE RIDGE THEN TURNING ENE ACROSS HISPANIOLA 
AND CONTINUING E ACROSS THE TROPICAL ATLC ALONG 22N. ANOTHER 
AREA OF DENSE CIRRUS...ORIGINATING FROM INTENSE CONVECTION OVER 
COLOMBIA...IS SPREADING NE ACROSS COLOMBIA AND OVER THE 
CARIBBEAN S OF 13N BETWEEN 70W AND 77W. OTHERWISE THE UPPER 
LEVELS APPEAR DRY SE OF A LINE FROM PANAMA TO THE VIRGIN 
ISLANDS. AT THE LOW LEVELS...ATLC HIGH PRESSURE N OF AREA IS 
MAINTAINING FRESH EASTERLY TRADES ACROSS THE CARIBBEAN WITH 
TYPICAL OROGRAPHIC SHOWERS ON ISLANDS WITH ELEVATED 
TERRAIN...AND STREAKS OF TRADE WINDS CUMULUS ELSEWHERE.   

ATLANTIC OCEAN...
THE UPPER LEVELS ARE QUITE COMPLICATED BUT BASICALLY AN UPPER 
TROUGH DOMINATES THE SUBTROPICAL ATLC BETWEEN 80W AND 70W...AND 
BETWEEN 55W AND 30W...AND OVER THE FAR E ATLC TO THE E OF 13W. 
DRY UPPER AIR IS INDICATED W OF 72W AND ALSO ALONG A 300 NM WIDE 
BAND CENTERED ALONG 30N70W TO 26N50W TO 27N33W. ANOTHER BAND OF 
DRY UPPER AIR IS NOTED WITHIN 150 NM EITHER SIDE OF LINE FROM 
11N30W TO 22N05W...AND DRY UPPER IS ALSO ROTATING CYCLONICALLY 
AROUND AN UPPER CYCLONE OVER NW AFRICA...ROUGHLY WITHIN 120 NM 
OF POINTS 30N12W TO 27N05W TO 31N02E. BROKEN CIRRUS IS OBSERVED 
ALONG A SHORTWAVE UPPER RIDGE...FROM 18N TO 23N BETWEEN 72W AND 
50W. SURFACE HIGH PRESSURE CENTERS ALONG 32N ARE MAINTAINING A 
FAIRLY TIGHT PRESSURE GRADIENT ACROSS MOST OF THE ATLC S OF 32N. 
HOWEVER...A DECAYING FRONTAL BOUNDARY SPLITS THE RIDGE ALONG 
32N58W TO 29N72W AND IS ACCOMPANIED BY BROKEN TOWERING CUMULUS 
AND LIGHT SHOWERS. SOME SHOWERS HAVE FORMED UNDER A DENSE CIRRUS 
SHIELD NEAR 23N70W AND WILL SPREAD RAPIDLY W ACROSS THE CENTRAL 
AND SOUTHERN BAHAMAS TONIGHT.  LOCALLY OVERCAST STRATOCUMULUS 
CLOUDS ARE SPREADING SW OVER THE E ATLC WATERS FROM 20N TO 30N 
BETWEEN 35W AND 18W. OTHERWISE LOCALLY BROKEN CUMULUS IS 
OBSERVED RACING ACROSS THE ATLC WATERS IN STRONG TRADES.  

$$
NELSON