000
AXPZ20 KNHC 180348
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC MON MAY 18 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 EXTENDS ALONG 08N77W TO 08N97W THROUGH LOW PRES 
NEAR 11N115W WITH THE AXIS CONTINUING SW TO 07N126W THEN W TO 
08N140W. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS NOTED 
WITHIN 150 NM EITHER SIDE OF LINE FROM 03N85W TO 08N86W...AND 
WITHIN 300 NM OF 10N101W...AND A LARGE AREA...SURROUNDING THE 
LOW PRESSURE...ROUGHLY WITHIN 240 NM EITHER SIDE OF LINE FROM 
17N110W TO 05N121W. OVERCAST LOW AND MID LEVEL CLOUDS...WITH 
ISOLATED SMALL CLUSTERS OF WEAK CONVECTION...IS NOTED FROM 07N 
TO 12N BETWEEN 122W AND 139W. 

...DISCUSSION...

ALOFT...TWO WELL DEFINED DEEP LAYERED CYCLONES ARE NOTICED. THE 
WESTERNMOST CYCLONE IS STATIONARY N OF HAWAII NEAR 31N156W WITH 
ITS ENVELOPE OF CYCLONIC FLOW EXTENDING E OVER THE DISCUSSION 
ALONG 24N140W TO 30N136W...DEFINED BY AN UPPER MOISTURE PLUME 
ALONG THE E PERIPHERY OF THE ANTICYCLONIC ENVELOPE. AN UPPER 
TROUGH THAT EXTENDS ACROSS EASTERN N AMERICA FROM NE TO SW 
CONTINUES W INTO THE DISCUSSION AREA FROM 30N94W TO 30N104W
BECOMING A SHEAR AXIS W INTO THE EASTERNMOST CYCLONE CENTERED 
NEAR 29N124W...WITH AN UPPER TROUGH CONTINUING S TO A BASE AT 
12N124W. AN UPPER LEVEL ANTICYCLONE ESTIMATED NEAR 07N136W HAS 
A SHORTWAVE RIDGE EXTENDING N TO A SHARP CREST 22N136W. A SECOND 
UPPER ANTICYCLONE HAS FORMED ALONG THE PARENT LONGWAVE RIDGE 
OVER NE UTAH WITH ANTICYCLONIC FLOW CONTINUING TO DOMINATE MOST 
OF WESTERN N AMERICA TO THE W AND N OF THE IMPRESSIVE TROUGH 
JUST 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 N AND W OF A LINE ALONG 13N140W 
TO 13N118W TO 26N107W. 

A QUASI STATIONARY UPPER ANTICYCLONE IS CENTERED NEAR 12N106W 
WITH A SHORTWAVE RIDGE CRESTING OVER OLD MEXICO ALONG POINTS
23N109W TO 24N101W TO 21N85W. UPPER DIFFLUENCE UNDER THIS 
BROAD RIDGE HAS BEEN ENHANCING CONVECTION ALONG AND N OF THE 
ITCZ BETWEEN 94W AND 121W...WITH SOME OF THE DEBRIS MOISTURE 
SPREADING NE ACROSS OLD MEXICO TO THE TOP OF THE RIDGE CREST
AND SPILLING SE ACROSS THE RIDGE AXIS OVER THE W GULF OF MEXICO.

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 78W WITH MOST OF THE 
RESULTANT DEBRIS MOISTURE ADVECTED NE ACROSS THE E CARIBBEAN 
INTO THE SUBTROPICAL CENTRAL N ATLC.
     
AT THE LOW LEVELS...A RIDGE EXTENDING ALONG 32N135W TO 25N130W 
TO 20N118W IS WEAKENING AND RETRACTING W WITH TIME. A LOW LEVEL 
REFLECTION OF THE UPPER CYCLONE IS ANALYZED AS A SURFACE TROUGH 
ALONG 123W FROM 30N TO 21N...AND DRIFTING W WITH TIME. THE 
GRADIENT N OF 25N BETWEEN THIS TROUGH AND RIDGE IS SUPPORTING N 
WINDS TO 20 KT AND SEAS TO 9 FT. THE TROUGH IS EXPECTED TO 
CONTINUE DRIFTING 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 MIDDAY 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 LATER 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 WITH HIGH PRESSURE BUILDING IN THE WAKE OF A COLD FRONT 
OVER WESTERN GULF OF MEXICO. THEY FEATURES ARE COMBINING TO 
DRIVE NORTHERLY 20 KT WINDS INTO THE GULF OF TEHUANTEPEC. 
EXPECTING THESE WINDS TO INCREASE TO 25 TO 30 KT LATE MON 
THROUGH AT LEAST LATE WED...WITH SOME GUIDANCE HINTING AT 
MINIMAL GALE.

$$
NELSON