000
AXPZ20 KNHC 211557
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC THU MAY 21 2009

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

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1545 UTC.

...ITCZ...

THE ITCZ AXIS EXTENDS ALONG 06N77W TO 12N120W TO 06N140W. WEAK 
SURFACE LOW PRES CENTERS ARE NOTED NEAR 09N96W AND 11N110W AND 
12N120W. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS NOTED 
WITHIN EITHER SIDE OF LINE FROM 05N77W TO 06N87W...AND WITHIN 
120 NM OF 11N95W...AND ALSO WITHIN 150 NM EITHER SIDE OF LINE 
FROM 12N106W TO 07N127W.

.DISCUSSION...

ALOFT...A MID TO UPPER CYCLONE IS IS OVER SOUTHERN CALIFORNIA AT 
34N119W WITH A MID LEVEL TROUGH EXTENDING SW INTO THE DISCUSSION 
AREA ALONG 30N118W TO 24N122W TO 22N132W TO 09N142W. AN UPPER 
RIDGE DOMINATES THE REGION N OF THIS TROUGH WITH A CREST NEAR 
29N124W. SOME UPPER MOISTURE IS OBSERVED WITHIN THE RIDGE TO THE 
N OF 30N W OF 130W...OTHERWISE THE UPPER LEVELS ARE VERY DRY N 
OF 20N W OF 110W...WITH THE UPPER LEVEL FLOW NEARLY ZONAL.

A SERIES OF TROPICAL UPPER ANTICYCLONES ARE NOTED ROUGHLY ALONG 
11N...NEAR 10.5N124W...NEAR 12N110W AND NEAR 11N101W. AN UPPER 
RIDGE EXTENDS E TO W THROUGH THESE ANTICYCLONES TO A WESTERN 
CREST AT 05N139W AND AN EASTERN CREST AT 08N86W. THE ASSOCIATED 
UPPER DIFFLUENCE UNDER THE RIDGE IS ENHANCING CONVECTION ALONG 
THE ITCZ WITH THE DEBRIS MOISTURE ADVECTED N TO ALONG 20N AND 
ADVECTED SW TO ALONG THE 02N...WITH THE MOISTURE EVAPORATING 
N OF 20N AND S OF 01N.     

AN UPPER ANTICYCLONE IS ESTIMATED NEAR 06N67W WITH A RIDGE 
EXTENDING W TO A CREST OVER THE PANAMA AND COSTA RICA BORDER. A 
DEEP LAYERED CYCLONE OVER THE E GULF OF MEXICO HAS AN UPPER 
TROUGH EXTENDING S TO 11N85W. CONVECTION IS ENHANCED ALONG THE 
PACIFIC ITCZ...TO THE N OF 05N E OF 86W...WITH THE DEBRIS 
MOISTURE EVAPORATING IN THE SAME AREA.
 
.AT THE LOW LEVELS...A RIDGE EXTENDS ALONG 32N137W TO 12N113W. 
NE TRADES AT 15 TO 20 KT ARE SW OF THE RIDGE...FROM 10 TO 15N W 
OF 130W...BUT ARE EXPECTED TO DIMINISH TO LESS THAN 20 KT 
FRI.    
THE SURFACE LOW NEAR 11.5N110W IS EXPECTED TO MOVE N TO NEAR 
13N110W FRI THEN MEANDER WITHOUT ANY SIGNIFICANT CHANGE THROUGH 
SAT.
  
GAP WINDS...
N TO NE WINDS 20 TO 25 KT WITH SEAS TO 7 FT WERE NOTED THIS 
MORNING IN AND JUST DOWNSTREAM OF OF GULF OF TEHUANTEPEC...BUT 
EXPECTED TO DIMINISH BELOW 20 KT THIS AFTERNOON.  

$$
NELSON