000
AXPZ20 KNHC 182156
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC MON MAY 18 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 
2145 UTC.

...ITCZ...

THE ITCZ AXIS EXTENDS ALONG 08N78W TO 10N93W TO 08N101W TO 
11N114W TO 03N140W. SCATTERED MODERATE ISOLATED STRONG 
CONVECTION IS NOTED WITHIN 150 NM EITHER SIDE OF LINE FROM 
05N77W TO 07N92W TO 13N105W AND WITHIN 30 NM EITHER SIDE OF LINE 
FROM 06N97W TO 05N105W TO 08N113W AND ALSO WITHIN 90 NM OF 
06N124W. OVERCAST LOW AND MID LEVEL CLOUDS...WITH ISOLATED SMALL 
CLUSTERS OF WEAK CONVECTION...IS NOTED FROM 04N TO 10N BETWEEN 
125W AND 140W. 

...DISCUSSION...

ALOFT...A DEEP LAYERED CYCLONE HAS CUT OFF NEAR 28N125W. AN 
UPPER TROUGH EXTENDS SE TO 17N113W AND IS MOVING NE WITH TIME.
AN UPPER LEVEL ANTICYCLONE IS CENTERED AT 10N135W WITH A 
SHORTWAVE RIDGE EXTENDING NE WITH ITS CREST FROM 21N140W TO A 
SHARP CREST AT 15N125W. SOME UPPER MOISTURE IS SPREADING INTO 
THE AREA NEAR 18N137W. OTHERWISE THESE UPPER FEATURES COMBINE TO 
DRY OUT THE UPPER LEVELS W OF 130W AND N OF 12N BETWEEN 130W AND 
118W.

A QUASI STATIONARY UPPER ANTICYCLONE IS CENTERED NEAR 11N105W 
WITH A SHORTWAVE RIDGE AMPLIFYING N TO A CREST OVER OLD MEXICO 
AT 29N106W. UPPER DIFFLUENCE UNDER THIS BROAD RIDGE HAS BEEN 
ENHANCING CONVECTION ALONG AND TO THE N OF THE ITCZ BETWEEN 83W 
AND 114W...WITH MOST OF THE DEBRIS MOISTURE SPREADING N OVER THE 
UPPER LEVELS OF OLD MEXICO TO THE S OF 28N...WITH SOME OF THE 
MOISTURE SPILLING SE ACROSS THE RIDGE OVER THE W CARIBBEAN.

A STATIONARY UPPER RIDGE EXTENDS W ACROSS NORTHERN VENEZUELA TO 
A CREST OVER W COLOMBIA. AN UPPER TROUGH EXTENDS S ALONG 74W 
ACROSS THE PANAMA AND COLOMBIA BORDER. THIS MID TO UPPER TROUGH 
SEPARATES THE FLOW ASSOCIATED WITH THE S AMERICAN RIDGE FROM THE 
TROPICAL E PACIFIC RIDGE DESCRIBED ABOVE. E PACIFIC ITCZ 
CONVECTION IS ENHANCED BETWEEN 83W AND 77W WITH SOME OF THE 
RESULTANT DEBRIS MOISTURE ADVECTED NE ACROSS THE E CARIBBEAN 
INTO THE SUBTROPICAL CENTRAL N ATLC.
     
AT THE LOW LEVELS...A RIDGE EXTENDS OVER THE AREA N OF 20N W OF 
130W. A LOW LEVEL TROUGH EXTENDS ALONG 33N123W TO 24N130W...AND
IS DRIFTING W WITH TIME. THE GRADIENT BETWEEN THIS TROUGH AND 
RIDGE IS SUPPORTING NE WINDS TO 20 KT AND SEAS TO 8 FT. THE 
TROUGH IS EXPECTED TO CONTINUE DRIFTING W BUT GRADUALLY FILL TUE 
NIGHT. THE GRADIENT E OF THE TROUGH ALONG THE W COAST OF THE 
BAJA PENINSULA FROM 23N TO 27N HAS TIGHTENED SOMEWHAT WITH 
SURGES OF NW WINDS TO 20 KT. THESE CONDITIONS ARE EXPECTED TO 
CONTINUE THROUGH LATE TUE.

GAP WINDS...HIGH PRESSURE OVER THE GULF OF MEXICO WILL CONTINUE 
TO DRIVE N WINDS AT 20 TO 30 KT THROUGH THE GULF OF TEHUANTEPEC 
FOR AT THE LEAST THE NEXT TWO DAYS. 

$$
NELSON