000
AXPZ20 KNHC 262117
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC TUE MAY 26 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 08N78W TO 10N96W TO 07N112W TO 
03N129W TO 05N140W. SCATTERED MODERATE CONVECTION IS WITHIN 
60 NM OF 08N79W. SCATTERED MODERATE CONVECTION IS FROM 03N TO 
12N BETWEEN 85W AND 94W. SCATTERED MODERATE CONVECTION IS FROM 
05N TO 12N BETWEEN 97W AND 114W.

.DISCUSSION...

A SURFACE RIDGE EXTENDS SOUTHWARD INTO THE NORTHERN WATERS FROM 
A 1025 MB SURFACE HIGH N OF THE AREA NEAR 36N133W. THE SURFACE 
HIGH AND RIDGE ARE BEING SUPPORTED BY SUBSIDENCE ASSOCIATED WITH 
AN UPPER LEVEL RIDGE APPROACHING THE SW UNITED STATES. THE 
SURFACE HIGH AND RIDGE CONTINUE TO DRIVE NE TO E TRADE WINDS UP 
TO 20 KT FROM 12N TO 20N W OF 125W...CONFIRMED BY THE QUIKSCAT 
PASS AROUND 26/1530 UTC. WAVEWATCH OUTPUT INDICATES SEAS TO 8 FT 
IN THIS REGION. DURING THE NEXT TWO DAYS...THE SURFACE HIGH IS 
FORECAST TO WEAKEN AS IT DRIFTS SOUTHEASTWARD AND A 
MID/UPPER-LEVEL SHORTWAVE TROUGH...WITH AN AXIS ALONG 138W N OF 
26N...MOVES EASTWARD. INSTABILITY ASSOCIATED WITH THIS TROUGH IS 
CURRENTLY SUPPORTING SCATTERED SHOWERS N OF 27N W OF 
132W...THOUGH DEEP CONVECTION IN THIS REGION IS BEING SUPPRESSED 
BY SUBSIDENCE ASSOCIATED WITH THE AFOREMENTIONED SURFACE HIGH 
AND RIDGE. AS THE SURFACE HIGH WEAKENS...ITS ASSOCIATED SURFACE 
PRESSURE GRADIENT WILL WEAKEN...WITH THE TRADE WINDS DIMINISHING 
BELOW 20 KT BY LATE TONIGHT.

A DEEP LAYER TROUGH CURRENTLY N OF THE DISCUSSION AREA IS 
FORECAST TO DIG SOUTHWARD DURING THE NEXT TWO DAYS AS AN UPPER 
LEVEL JET MAXIMUM DIVES SOUTHEASTWARD TOWARD THE TROUGH AXIS. AN 
ASSOCIATED COLD FRONT WILL ENTER FAR NW PORTIONS OF THE 
DISCUSSION AREA BY LATE THU INTO EARLY FRI...WITH SOUTHERLY 
WINDS INCREASING TO 20 KT AHEAD OF THE FRONT. HOWEVER... 
CONSENSUS AMONG GLOBAL MODELS IS THAT AN UPPER LOW WILL CUT OFF 
OVER THE SOUTHERN EXTENT OF THE TROUGH BY LATE SATURDAY NW OF 
THE DISCUSSION AREA. THE FRONT WILL CORRESPONDINGLY WEAKEN BY 
EARLY IN THE WEEKEND WITH DEEP LOW PRESSURE REMAINING N OF THE 
AREA...AND WINDS OVER THE NW FORECAST WATERS DIMINISHING. 
HOWEVER...STRONG WINDS AROUND THE SURFACE LOW N OF THE AREA WILL 
RESULT IN SEAS OF 8 TO 9 FT IN NW SWELL ENTERING THE NW WATERS 
THIS WEEKEND.

THE SURFACE PRESSURE GRADIENT BETWEEN THE SURFACE RIDGE OVER THE 
N WATERS AND A SURFACE TROUGH OVER MEXICO IS RESULTING IN NW TO 
N WINDS OF 20 TO 25 KT FROM 20N TO 23N BETWEEN 107W AND 
114W...REVEALED BY THE QUIKSCAT PASS AROUND 26/1345 UTC. THESE 
WINDS ARE ALSO BEING ENHANCED BY VARIATIONS IN TERRAIN ALONG THE 
COAST OF MEXICO. THIS AREA OF WINDS IS FORECAST TO CONTINUE TO 
AFFECT THE FAR EASTERN WATERS DURING THE NEXT FEW DAYS...THOUGH 
THE AREA IS FORECAST TO SLIDE SOUTHWARD IN CORRESPONDENCE WITH 
THE MOTION OF THE AFOREMENTIONED SURFACE HIGH.

AS FOR CONVECTION...A SURFACE TROUGH EMBEDDED WITHIN THE ITCZ 
EXTENDS FROM 13N133W TO 04N139W...WITH LOW LEVEL CONVERGENCE 
SUPPORTING SCATTERED MODERATE CONVECTION WITHIN 60 NM EITHER 
SIDE OF THIS TROUGH. THIS CONVECTION IS ALSO BEING SUPPORTED BY 
UPPER LEVEL DIVERGENCE ASSOCIATED WITH AN UPPER LEVEL HIGH 
CENTERED NEAR 06N140W AND AN ASSOCIATED UPPER LEVEL RIDGE AXIS 
EXTENDING FROM THE UPPER LEVEL HIGH TO 07N123W. ADDITIONALLY...A 
BROAD UPPER LEVEL RIDGE IS OVER THE E PACIFIC FROM 03N TO 16N E 
OF 115W. UPPER LEVEL DIVERGENCE AND DEEP LAYER MOISTURE NEAR 
THIS FEATURE ARE ENHANCING THE CONVECTION ASSOCIATED WITH THE 
ITCZ.

$$
COHEN