000
AXPZ20 KNHC 180947
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC SUN APR 18 2010

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM 
THE EQUATOR TO 32N...EAST OF 140W. 

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0945 UTC.

...ITCZ...

THE ITCZ AXIS EXTENDS ALONG 06N78W TO 09N100W TO 05N116W TO 
09N133W TO 07N140W. ISOLATED MODERATE TO STRONG CONVECTION IS 
OBSERVED WITHIN 240 NM EITHER SIDE OF A LINE FROM 12N87W TO 
04N110W. SCATTERED MODERATE ISOLATED STRONG IS DISSIPATING FROM 
04N TO 10N BETWEEN 122W AND 132W.

...DISCUSSION...

A COMPLEX UPPER LEVEL CYCLONE CONTINUES TO DOMINATE THE NW 
PORTION OF THE DISCUSSION AREA DRIVING TWO SURFACE CYCLONES INTO 
THE AREA. THE MEAN UPPER CYCLONE IS NEAR 26N136W WITH A TROUGH 
SW TO BEYOND 22N140W. DRY UPPER AIR IS WRAPPING AROUND ITS THE 
SOUTHERN SEMICIRCLE OF THE CYCLONE...GENERALLY SW OF LINE FROM  
25N131W TO 28N140W. UPPER MOISTURE IS NOTED OVER THE AREA NE OF 
THE CYCLONE CENTER.
 
AN UPPER LEVEL ANTICYCLONE IS CENTERED NEAR 05N118W 11N126W WITH 
AN UPPER RIDGE EXTENDING W TO BEYOND 10N140W AND A RIDGE EXTENDS 
NE THROUGH 32N 117W TO A CREST OVER SOUTHERN NEVADA. BROAD 
ANTICYCLONIC CIRCULATION DOMINATES THE UPPER LEVELS OF THE 
DISCUSSION AREA W OF 106W. ITCZ CONVECTION WAS ENHANCED EARLIER 
UNDER THE RIDGE S OF 10N BETWEEN 115W AND 133W. SOME OF THE 
DEBRIS MOISTURE IS SPREADING S ACROSS THE EQUATOR BETWEEN 115W 
AND 130W...AND SOME OF THE MOISTURE IS ALSO ADVECTED NW ALONG 
THE WESTERN RIDGE TO NEAR 15N135W...WHERE IT MERGES WITH A MORE 
PRONOUNCED TROPICAL PLUME THAT ORIGINATES OVER THE DEEP TROPICAL 
CENTRAL PACIFIC. THE COMBINED PLUME CONTINUES NE ACROSS THE 
DISCUSSION AREA ALONG THE PERIPHERY OF THE LARGE UPPER 
RIDGE...ROUGHLY WITHIN 300 NM EITHER SIDE OF LINE FROM 16N135W 
TO 24N123W THEN FANS OUT ACROSS THE RIDGE CREST OVER THE AREA 
FROM 20N TO 35N BETWEEN 123W AND 110W. THE MOISTURE EVAPORATES 
OVER WESTERN OLD MEXICO INTO DRY UPPER AIR DESCRIBED LATER.

AN UPPER TROUGH EXTENDS SE OVER EASTERN OLD MEXICO ALONG 32N102W 
TO 18N92W TO A BASE OVER THE TROPICAL PACIFIC NEAR 06N92W. AN 
UPPER RIDGE EXTENDS W FROM S AMERICA ACROSS CENTRAL AMERICA TO 
BROAD CREST ESTIMATED AT 10N85W. VERY DRY UPPER AIR IS INDICATED 
UNDER THE TROPICAL PACIFIC UPPER RIDGE...FROM 08N TO 20N E OF 
120W...MERGING WITH DRY UPPER AIR ADVECTED SE TO THE W OF THE 
UPPER TROUGH AXIS...ROUGHLY WITHIN 240 NM W OF LINE 27N105W TO 
12N90W. DIFFLUENCE E OF THE MEXICAN UPPER TROUGH AXIS ENHANCED 
CONVECTION WITH THE DEBRIS MOISTURE SPREADING NE ACROSS THE GULF 
OF MEXICO AND GUATEMALA AND HONDURAS. ITCZ CONVECTION IS ALSO 
ENHANCED JUST E OF THE UPPER TROUGH...AND WAS ENHANCED EARLIER 
UNDER THE W END OF THE TROPICAL RIDGE. THE RESULTANT DEBRIS 
MOISTURE IS ADVECTED NE ACROSS CENTRAL AMERICA TO THE E OF 86W. 
ALL OF THIS DEBRIS MOISTURE HAS THE UPPER LEVELS OF THE TROPICS 
QUITE MOIST FROM MEXICO TO THE BAHAMAS AND TO THE CENTRAL 
CARIBBEAN.

AT THE SURFACE...HIGH PRES OF 1018 MB IS CENTERED AT 26N122W AND 
IS BEGINNING TO LOSE IDENTITY AS A WEAK SURFACE RIDGE BECOMES 
ORIENTATED NW TO SE OVER THE AREA N OF 15N ALONG 117W. THIS 
WEAKENING RIDGE WILL ALLOW THE APPROACHING LOW PRESSURE SYSTEMS 
AND WEAK COLD FRONTS TO ADVANCE E TO ALONG 120W BEFORE 
DISSIPATING. THE PRESSURE GRADIENT BETWEEN THIS RIDGE AND THE 
FRONTS WILL SUPPORT SOUTHERLY 20 TO 30 KT. THE GRADIENT W OF THE 
FRONT WILL ALSO SUPPORT 20 TO 30 KT WITH MINIMAL GALE CONDITIONS 
JUST W OF THE AREA. THESE W WINDS WILL DRIVE SEAS TO ABOUT 15 FT 
INTO AREA...NOTING THAT FORECAST MAX SEAS IS SLIGHTLY BELOW 
GUIDANCE.
   
FURTHER S...NE TRADES WILL INCREASE AGAIN TO 20 KT IN ABOUT 48 
HOURS AS HIGH PRESSURE BUILDS SE OVER THE AREA W OF 120W IN THE 
WAKE OF THE DISSIPATING FRONTS. CONFUSED SEAS OVER THE TROPICS 
IN THE MULTIPLE SWELL COMPONENTS WILL DIMINISH THROUGH 48 
HOURS.   

$$
NELSON