000
AXPZ20 KNHC 160343
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC SAT MAY 16 2009

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

BASED ON 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0315 UTC.

...ITCZ...

THE ITCZ AXIS IS ALONG POINTS 05N77W TO 12N110W TO 05N140W. 
SCATTERED MODERATE ISOLATED STRONG STRONG CONVECTION IS NOTED 
WITHIN 180 NM EITHER SIDE OF LINE FROM 04N86W TO 11N110W TO 
08N127W THEN NARROW TO WITHIN 120 NM OF LINE TO 04N140W. 

...DISCUSSION...

ALOFT...AN UPPER LEVEL ANTICYCLONE IS ESTIMATED JUST W OF THE 
REGION AT 07N150W WITH A LARGE AMPLITUDE RIDGE EXTENDING NE 
ALONG 35N130W CRESTING OVER 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 137W AND IS BEGINNING TO EVAPORATE. 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 27N117W WITH TROUGH CONTINUING SW TO BASE 
NEAR 15N130W. VERY DRY UPPER AIR IS INDICATED ELSEWHERE NW OF A 
LINE FROM 07N140W TO CENTRAL OLD MEXICO AT 26N103W. 

AN UPPER ANTICYCLONE IS CENTERED AT 14N101W WITH A SHORTWAVE 
RIDGE EXTENDING N ACROSS OLD MEXICO ALONG 23N100W TO A CREST AT 
28N98W. UPPER DIFFLUENCE UNDER THIS BROAD RIDGE IS ENHANCING 
CONVECTION ALONG AND N OF THE ITCZ BETWEEN 85W AND 125W WITH 
SOME OF THE DEBRIS MOISTURE SPREADING NE ACROSS OLD MEXICO TO 
THE S OF 25N SPILLING OVER THE SW GULF OF MEXICO.

A STATIONARY UPPER RIDGE EXTENDS W ACROSS NORTHERN VENEZUELA AND 
COLOMBIA TO A CREST OVER EASTERN PANAMA. AN UPPER CYCLONE OVER 
THE FLORIDA STRAITS HAS CUT 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 04S82W SEPARATING THE FLOW ASSOCIATED WITH THE S 
AMERICAN RIDGE FROM THE TROPICAL E PACIFIC RIDGE DESCRIBED 
ABOVE. ITCZ CONVECTION IS ENHANCED ALONG THE E PERIPHERY OF 
PACIFIC RIDGE AND SEEMS TO BE DISSIPATING ELSEWHERE IN THE 
DISCUSSION AREA E OF 82W. 
     
AT THE LOW LEVELS...A RIDGE EXTENDS SE FROM 32N134W TO 17N105W. 
THE GRADIENT NE OF THE RIDGE IS SUPPORTING NORTHERLY WINDS AT 20 
KT OVER THE PACIFIC WATERS N OF 23N BETWEEN 126W AND 118W WITH 
THE MAXIMUM SEAS HEIGHTS CURRENTLY AT 12 FT NEAR 30N125W IN THE 
N SWELL. THIS GRADIENT SHOULD RELAX SOME LATER 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 EARLY SAT 
AS THE RIDGE WEAKENS.       

GAP WINDS...A BROAD TROUGH IS EXPECTED TO DOMINATE THE EASTERN 
GULF OF MEXICO EARLY NEXT WEEK SETTING UP THE CONDITIONS FOR N
WINDS AT 20 KT TO BRIDGE THE ISTHMUS OF TEHUANTEPEC INTO THE 
GULF OF TEHUANTEPEC SUN NIGHT INCREASING TO 25 TO 30 KT LATE MON.

$$
NELSON