000
AXPZ20 KNHC 152157
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC FRI MAY 15 2009

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

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2100 UTC.

...ITCZ...

THE ITCZ AXIS IS ALONG POINTS 08N78W TO 07N75W TO 13N107W TO 
05N140W. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS NOTED 
WITHIN 180 NM EITHER SIDE OF LINE FROM 03N87W TO 12N106W TO 
08N120W TO 09N127W TO 04N140W. SCATTERED MODERATE ISOLATED 
STRONG CONVECTION IS ALSO OBSERVED WITHIN 60 NM OF 12.5N91.5W.

...DISCUSSION...

ALOFT...AN UPPER LEVEL ANTICYCLONE IS ESTIMATED JUST W OF THE 
REGION AT 21N146W WITH A LARGE AMPLITUDE RIDGE EXTENDING NE 
ALONG 40N130W TO CANADA NEAR 60N127W. SOME UPPER MOISTURE THAT 
ORIGINATED IN THE W PACIFIC IS NOW SPILLING ACROSS THE RIDGE 
OVER THE UPPER LEVELS OF THE DISCUSSION AREA TO THE N OF 25N 
BETWEEN 125W AND 138W. AN UPPER TROUGH DISSECTING THE CENTRAL 
UNITED STATES EXTENDS SW ACROSS THE N PORTION OF THE DISCUSSION 
AREA FROM 32N107W THROUGH AN UPPER CYCLONE AT 27N118W WITH 
TROUGH CONTINUING SW TO BASE NEAR 16N134W. VERY DRY UPPER AIR IS 
INDICATED ELSEWHERE N OF THE ITCZ AT 07N140W TO CENTRAL OLD 
MEXICO AT 25N104W. 

AN UPPER ANTICYCLONE IS CENTERED AT 13N102W WITH A SHORTWAVE 
RIDGE EXTENDING N ACROSS OLD MEXICO ALONG 23N102W TO A CREST AT 
31N100W. UPPER DIFFLUENCE UNDER THIS BROAD RIDGE IS ENHANCING 
CONVECTION ALONG AND N OF THE ITCZ BETWEEN 85W AND 128W WITH 
SOME OF THE DEBRIS MOISTURE SPREADING NE ACROSS OLD MEXICO S OF 
24N AND OVER THE SW GULF OF MEXICO.

A STATIONARY UPPER RIDGE EXTENDS W ACROSS NORTHERN VENEZUELA AND 
COLOMBIA TO A CREST OVER PANAMA. AN UPPER CYCLONE OVER THE 
CENTRAL BAHAMAS IS CUTTING OFF FROM ITS PARENT UPPER TROUGH OVER 
THE CENTRAL N ATLANTIC. AN TROUGH EXTENDS SW FROM THIS CYCLONE 
ACROSS THE W CARIBBEAN ACROSS COSTA RICA INTO AN UPPER CYCLONE 
NEAR 03S80W SEPARATING THE FLOW ASSOCIATED WITH THIS S AMERICAN 
RIDGE FROM THE TROPICAL E PACIFIC RIDGE DESCRIBED ABOVE. ITCZ 
CONVECTION IS ENHANCED ALONG THE PERIPHERY OF BOTH RIDGES OVER 
THE AREA FROM 03N TO 10N BETWEEN 77W AND 87W. 
     
AT THE LOW LEVELS...A RIDGE EXTENDS SE FROM 32N131W TO 17N105W. 
THE GRADIENT NE OF THE RIDGE IS SUPPORTING NORTHERLY WINDS 20 TO 
25 KT OVER THE PACIFIC WATERS N OF 24N BETWEEN 126W AND 118W 
WITH THE MAXIMUM SEAS HEIGHTS CURRENTLY AT 13 FT NEAR 31N121W IN 
THE N SWELL. THIS GRADIENT SHOULD RELAX SOME TONIGHT AND SAT AS 
THE RIDGE WEAKENS AND RETRACTS W AND ALLOWS A BROAD LOW LEVEL 
TROUGH TO DRIFT W OVER THE AREA N OF 25N AND E OF 125W THROUGH 
SUN. A SMALL AREA OF NE TRADES CURRENTLY TO 20 KT ARE OBSERVED S 
OF THE RIDGE BUT ARE EXPECTED TO DIMINISH BELOW 20 KT TONIGHT 
AND EARLY SAT AS THE RIDGE WEAKENS.       

GAP WINDS...N WINDS MAY INCREASE IN N WINDS 20 TO 25 KT IN THE 
GULF OF TEHUANTEPEC SUN NIGHT.

$$
NELSON