000
AXPZ20 KNHC 170338
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC SUN MAY 17 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 15N109W TO 10N116W TO 
07N140W. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS NOTED 
WITHIN 90 NM EITHER SIDE OF LINE FROM 09N79W TO 06N86W...AND 
ALSO WITHIN 180 NM EITHER SIDE OF LINE FROM 14N111W TO 
07N119W...THEN NARROWS WITHIN 60 NM EITHER SIDE OF LINE FROM 
07N130W TO 09N135W.

...DISCUSSION...

ALOFT...AN UPPER LEVEL ANTICYCLONE IS ESTIMATED NEAR 04N138W 
WITH A LARGE AMPLITUDE RIDGE EXTENDING NE ALONG 27N139W AND 
35N130W AND CRESTING OVER CANADA NEAR 60N120W. IMMEDIATELY TO 
THE SE OF THIS LARGE RIDGE IS AN UPPER TROUGH THAT DISSECTS N 
AMERICA FROM NE TO SW INTO THE DISCUSSION AREA FROM 32N114W 
THROUGH AN UPPER CYCLONE AT 26N118W WITH TROUGH CONTINUING SW TO 
BASE NEAR 13N136W. VERY DRY UPPER AIR IS INDICATED OVER MOST OF 
THE W PORTION OF THE AREA...ROUGHLY TO THE W OF A LINE ALONG
13N140W TO 14N120W TO 25N104W. 

A QUASI STATIONARY UPPER ANTICYCLONE IS CENTERED NEAR 12N103W 
WITH A SHORTWAVE RIDGE EXTENDING NE ACROSS OLD MEXICO ALONG 
20N99W TO A CREST AT 28N92W. UPPER DIFFLUENCE UNDER THIS BROAD 
RIDGE HAS BEEN ENHANCING CONVECTION ALONG AND N OF THE ITCZ 
BETWEEN 85W AND 120W WITH SOME OF THE DEBRIS MOISTURE SPREADING 
NE ACROSS OLD MEXICO TO THE S OF 25N AND SPILLING E ACROSS THE 
RIDGE AXIS OVER THE SW GULF OF MEXICO AND OVER THE YUCATAN 
PENINSULA.

A STATIONARY UPPER RIDGE EXTENDS W ACROSS NORTHERN VENEZUELA AND 
COLOMBIA TO A CREST OVER THE COLOMBIA AND PANAMA BORDER. AN 
UPPER CUT OFF CYCLONE OVER THE SW CUBA HAS AN UPPER TROUGH 
EXTENDING S ALONG 80W CROSSING THE EQUATOR AT 79W INTO AN UPPER 
CYCLONE NEAR 03S80W. THIS MID TO UPPER TROUGH SEPARATES 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 BETWEEN 85W AND 77W WITH THE DEBRIS 
MOISTURE ADVECTED NE ACROSS THE SE CARIBBEAN.
     
AT THE LOW LEVELS...A RIDGE EXTENDS SE FROM 31N138W TO 16N105W. 
THE GRADIENT NE OF THE RIDGE IS BEGINNING TO RELAX EFFECTIVELY 
SHRINKING THE AREA OF NORTHERLY WINDS TO 20 KT AND SEAS TO 9 FT 
TO THE WATERS N OF 26N BETWEEN 127W AND 117W. THE GRADIENT 
SHOULD CONTINUE TO RELAX TONIGHT AS THE RIDGE WEAKENS AND 
RETRACTS W ALLOWING A BROAD LOW LEVEL TROUGH TO DRIFT W OVER THE 
AREA N OF 25N AND E OF 127W THROUGH MON. EXPECTING NORTHERLY 
WINDS TO 20 KT TO SET UP ALONG THE W SIDE OF THE TROUGH AS ITS 
SHIFTS W ACROSS THE NORTHERN WATERS. 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 INVERTED TROUGH IS EXPECTED TO DOMINATE THE 
EASTERN GULF OF MEXICO EARLY NEXT WEEK AND A COLD FRONT WILL 
SWEEP SE ACROSS THE WESTERN GULF OF MEXICO SETTING UP THE 
CONDITIONS FOR N WINDS AT 20 KT TO BRIDGE THE ISTHMUS OF 
TEHUANTEPEC INTO THE GULF OF TEHUANTEPEC LATE SUN NIGHT 
INCREASING TO 25 TO 30 KT LATE MON.

$$
NELSON