000
AXNT20 KNHC 210556
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 AM EDT FRI APR 21 2006

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL 
AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHEASTERN 
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...WEATHER OBSERVATIONS... 
RADAR...AND METEOROLOGICAL ANALYSIS.

BASED ON 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0345 UTC.

...ITCZ...
ITCZ AXIS IS CENTERED ALONG 8N13W 1N30W 1N48W. SCATTERED SHOWERS 
AND ISOLATED TSTMS ARE NOTED WITHIN 240 NM EITHER SIDE OF AXIS 
BETWEEN 10W AND 26W AND BETWEEN 35W AND 47W. ISOLATED SHOWERS 
AND TSTMS WERE ALSO NOTED WITHIN 15 NM OF LINE 6N27W 4N34W.

...DISCUSSION...
GULF OF MEXICO...
ALOFT...A BROAD SHORTWAVE RIDGE DOMINATES THE GULF OF MEXICO 
ORIGINATING FROM A TROPICAL ANTICYCLONE CENTERED OVER THE E PAC 
NEAR 8N98W. THUS THE UPPER AIR IS DRY AND THE FLOW NEARLY ZONAL 
OVER MOST OF THE GULF. THE EXCEPTION IS THAT UPPER DIFFLUENCE IS 
ENHANCING CONVECTION ALONG A SURFACE FRONT OVER THE EXTREME NE 
TEXAS COASTAL PLAINS...WITH THE DEBRIS MOISTURE ADVECTED ENE AND 
JUST BARELY ENTERING THE EXTREME NW GULF OF MEXICO COASTAL 
WATERS. DEBRIS MOISTURE ORIGINATING FROM AFTERNOON SEABREEZE 
CONVECTION OVER OLD MEXICO...BETWEEN 17N TO 25N...IS NOW 
SPREADING ENE ACROSS THE SW WATERS...ROUGHLY S OF 25N W OF 90W. 
A 1016 MB HIGH IS CENTERED OVER THE FLORIDA BIG BEND WITH A 
RIDGE EXTENDING W ALONG 29N. THIS HIGH IS EXPECTED TO SHIFT E OF 
THE GULF TODAY WITH ITS ASSOCIATED RIDGE SHIFTING SLIGHTLY S TO 
ALONG 28N AS THE WEAK SURFACE FRONT MOVES INTO THE NW WATERS AND 
DISSIPATES.

CARIBBEAN SEA...
ALOFT...A BROAD SHORTWAVE RIDGE DOMINATES THE CARIBBEAN W OF 77W 
ORIGINATING FROM A TROPICAL ANTICYCLONE CENTERED OVER THE E PAC 
NEAR 8N98W. THE UPPER WLY FLOW TURNS CYCLONIC TO THE E OF 77W 
AND INTO AN UPPER TROUGH EXTENDING S INTO THE CARIBBEAN WITH ITS 
MEAN AXIS N OF 14N ALONG 72W. UPPER DEBRIS MOISTURE FROM 
AFTERNOON CONVECTION OVER GUATEMALA...BELIZE...AND HONDURAS IS 
NOW SPREADING E OVER THE GULF OF HONDURAS.  AT THE LOW LEVELS 
ELY TRADES DOMINATE THE CARIBBEAN WITH THE GRADIENT STRONGEST S 
OF 13N AND OVER THE GULF OF HONDURAS. LATEST IMAGERY SUGGESTS A 
TROUGH IS DEVELOPING JUST NE OF THE GULF OF HONDURAS WITH 
CYCLONIC TURNING CENTERED ON 18N83W. AN AREA OF OVERCAST LOW 
CLOUDS AND SCATTERED SHOWERS IS NOTED WITHIN 90 NM OF 16N80W. 
THE CONVECTION IN THIS AREA MAY BE ENHANCED LATER TODAY IF THE 
LOW LEVEL TROUGH CONTINUES TO DEVELOP. OTHERWISE...LITTLE CHANGE 
EXPECTED NEXT FEW DAYS. 

ATLANTIC OCEAN...
A LONG WAVE TROUGH DOMINATES THE UPPER LEVELS OF THE NW ATLC. AN 
EMBEDDED DEEP-LAYERED CYCLONE IS CENTERED NEAR 40N60W WITH A 
TROUGH EXTENDING S INTO THE DISCUSSION AREA ALONG 32N63W TO 
BEYOND 20N68W INTO THE CARIBBEAN. AN EMBEDDED CYCLONE WAS NOTED 
EARLIER NEAR 28N74W BUT HAS WEAKENED WITH ONLY WEAK TROUGHINESS 
SUGGESTED AT THE LOW LEVELS JUST N OF THE BAHAMAS...ROUGHLY FROM 
27N79W TO 30N76W. BROKEN LOW AND MID LAYERED CLOUDS...AND WEAK 
SHOWERS...ARE NOTED WITHIN 90 NM OF 28N76W. A FRONTAL TROUGH 
CONTINUES TO WEAKEN ALONG 32N50W 23N65W. BROKEN TO LOCALLY 
OVERCAST LOW AND MID LAYERED CLOUDS ARE OBSERVED WITHIN 360 NM 
EITHER SIDE OF THIS DECAYING FRONT. UPPER DIFFLUENCE E OF THE 
UPPER TROUGH IS ENHANCING CONVECTION WITHIN 30 NM EITHER SIDE OF 
LINE 32N45W 19N57W...LIKELY ALONG A WEAKENED PRE-FRONTAL TROUGH. 
DEBRIS MOISTURE FROM THIS CONVECTION IS ADVECTED NE AND E IN 
ASSOCIATION WITH AN UPPER RIDGE THAT ORIGINATES NEAR 6N60W...AND 
EXTENDS NE TO WELL BEYOND 32N43W AND CRESTING NEAR 50N33W ATTM. 
CONVECTIVE DEBRIS MOISTURE SPILLS E ACROSS THE RIDGE COVERING 
THE DISCUSSION AREA N OF 23N BETWEEN 49W AND 35W.

AN UPPER TROUGH ORIGINATES FROM A CYCLONE JUST OFF THE NW COAST 
OF SPAIN AND EXTENDS SW INTO THE DISCUSSION AREA ALONG 32N19W 
23N27W TO A BASE NEAR 12N47W. A BAND OF DRY UPPER AIR IS NOTED 
WITHIN 240 NM EITHER SIDE OF LINE 30N1W 22N17W 13N48W. UPPER 
MOISTURE IS INDICATED NW OF THE UPPER TROUGH E OF 35W. A BROAD 
UPPER ANTICYCLONE IS NOTED OVER AFRICA NEAR 15N5E WITH A RIDGE 
EXTENDING W OFF THE AFRICAN COAST AT 10N16W TO S AMERICA NEAR 
2N46W. UPPER DIFFLUENCE IS ENHANCING ITCZ CONVECTION DESCRIBED 
ABOVE. AT THE LOW LEVELS HIGH PRES IS CENTERED NEAR 33N33W WITH 
A RIDGE SW TO NEAR 18N60W. LOCALLY BROKEN STRATOCUMULUS IS NOTED 
SE OF THE RIDGE AXIS. SAHARAN DUST WAS OBSERVED ON YESTERDAYS 
VISIBLE IMAGERY E OF 25W FROM 10N-20N. 

$$
NELSON