000
AXPZ20 KNHC 172159
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC SUN MAY 17 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 EXTENDS ALONG 09N79W TO 09N103W TO AN EMBEDDED LOW 
PRES 1009 MB AT 11N116W WITH THE AXIS CONTINUING SW TO 07N121W 
THEN W TO 08N140W. SCATTERED MODERATE ISOLATED STRONG CONVECTION 
IS NOTED WITHIN 60 NM EITHER SIDE OF LINE FROM 07N83W TO 
04N86W...AND WITHIN A LARGE AREA BOUNDED FROM 06N TO 15N BETWEEN 
93W AND 104W...AND ALSO WITHIN ANOTHER AREA...SURROUNDING THE 
LOW PRESSURE...ROUGHLY 240 NM EITHER SIDE OF LINE FROM 15N110W 
TO 07N121W. OVERCAST LOW AND MID LEVEL CLOUDS...WITH ISOLATED 
SMALL CLUSTERS OF WEAK CONVECTION...IS NOTED FROM 07N TO 12N 
BETWEEN 122W AND 142W. 

...DISCUSSION...

ALOFT...TWO WELL DEFINED DEEP LAYERED CYCLONES ARE NOTICED. THE 
WESTERNMOST CYCLONE IS N OF HAWAII NEAR 31N155W WITH ITS 
ENVELOPE OF CYCLONIC FLOW EXTENDING E OVER THE DISCUSSION AREA 
TO THE N OF 26N W OF 137W...DEFINED BY AN UPPER MOISTURE PLUME 
OVER THE AREA N OF 22N BETWEEN 137W AND 147W. AN UPPER TROUGH 
THAT DISSECTS N AMERICA FROM NE TO SW ACROSS THE GREAT LAKES 
CONTINUES W INTO THE DISCUSSION AREA FROM 30N99W TO 30N120W THEN 
S INTO THE EASTERNMOST CYCLONE CENTERED NEAR 28N123W...WITH AN 
UPPER TROUGH CONTINUING S TO 12N124W. AN UPPER LEVEL ANTICYCLONE 
ESTIMATED NEAR 07N136W HAS A SHORTWAVE RIDGE EXTENDING N TO A 
SHARP CREST 25N136W. A SECOND UPPER ANTICYCLONE HAS FORMED ALONG 
THE PARENT LONGWAVE RIDGE OVER UTAH WITH ANTICYCLONIC FLOW 
CONTINUING TO DOMINATE MOST OF WESTERN N AMERICA TO THE W OF THE 
IMPRESSIVE TROUGH ALREADY MENTIONED. THE RESULT OF THESE UPPER 
FEATURES IS A LARGE AREA OF VERY DRY UPPER AIR OVER MOST OF THE 
W PORTION OF THE DISCUSSION AREA...ROUGHLY TO THE W OF A LINE 
ALONG 13N140W TO 14N120W TO 25N106W. 

A QUASI STATIONARY UPPER ANTICYCLONE IS CENTERED NEAR 13N104W 
WITH A SHORTWAVE RIDGE EXTENDING NE ACROSS OLD MEXICO ALONG 
18N97W TO A CREST AT 24N89W. UPPER DIFFLUENCE UNDER THIS BROAD 
RIDGE HAS BEEN ENHANCING CONVECTION ALONG AND N OF THE ITCZ 
BETWEEN 91W AND 122W...WITH SOME OF THE DEBRIS MOISTURE 
SPREADING NE ACROSS OLD MEXICO TO THE S OF 24N...SPILLING E 
ACROSS THE RIDGE AXIS OVER THE SW GULF OF MEXICO...THE YUCATAN 
PENINSULA...GUATEMALA AND THE GULF OF HONDURAS.

A STATIONARY UPPER RIDGE EXTENDS W ACROSS NORTHERN VENEZUELA AND 
COLOMBIA TO A CREST OVER THE COLOMBIA AND PANAMA BORDER. A DEEP 
LAYERED CYCLONE OVER JAMAICA HAS AN UPPER TROUGH EXTENDING SSW 
ACROSS W PANAMA CROSSING THE EQUATOR AT 80W. 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 88W AND 77W WITH THE DEBRIS 
MOISTURE ADVECTED NE ACROSS THE SE CARIBBEAN.
     
AT THE LOW LEVELS...A RIDGE EXTENDING ALONG 32N135W TO 25N130W 
TO 20N118W IS WEAKENING AND RETRACTING W WITH TIME. THE UPPER 
CYCLONE NEAR 28N123W HAS DEEPENED WITH A SURFACE TROUGH FORMING 
FROM 30N123W TO 23N124W. THE GRADIENT N OF 27N BETWEEN THIS 
TROUGH AND RIDGE IS SUPPORTING N WINDS TO 20 KT AND SEAS TO 9 
FT. THE TROUGH IS EXPECTED TO DRIFT W OVER THE NEXT FEW DAYS 
WITH LITTLE CHANGE IN THE CONDITIONS W OF THE TROUGH. THE 
GRADIENT WILL ALSO TIGHTEN E OF THE TROUGH ALONG THE W COAST OF 
THE BAJA PENINSULA FROM 23N TO 27N EARLY MON SUPPORTING NW WINDS 
TO 20 KT WITH CONDITIONS CONTINUING THROUGH TUE. A SMALL AREA OF 
NE TRADES CURRENTLY TO 20 KT...SEAS TO 8 FT...ARE OBSERVED S OF 
THE RIDGE BUT ARE EXPECTED TO DIMINISH BELOW 20 KT TONIGHT AS 
THE RIDGE WEAKENS.       

GAP WINDS...A BROAD TROUGH IS EXPECTED TO DOMINATE THE EASTERN 
GULF OF MEXICO...NW CARIBBEAN AND FLORIDA STRAITS OVER THE NEXT 
FEW DAYS AND HIGH PRESSURE IN THE WAKE OF FRONT OVER WESTERN 
GULF OF MEXICO HAVE COMBINED TO SET UP THE CONDITIONS FOR N 
WINDS TO PULSE TO 20 KT INTO THE GULF OF TEHUANTEPEC. EXPECT 
THESE WINDS TO INCREASE TO 25 TO 30 KT LATE MON THROUGH AT LEAST 
LATE WED...WITH SOME GUIDANCE HINTING AT MINIMAL GALE.

$$
NELSON