000
AXPZ20 KNHC 191558
TWDEP 

TROPICAL WEATHER DISCUSSION   
NWS NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC THU MAY 19 2011

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 
1500 UTC.
 
...ITCZ...
AXIS ALONG 10N86W TO 05N114W TO 04N140W.  SCATTERED MODERATE 
CONVECTION WITHIN 180 NM OF AXIS E OF 108W.  ISOLATED MODERATE 
CONVECTION WITHIN 150 NM N OF AXIS W OF 118W.

...DISCUSSION...
UPPER LEVEL TROUGH EXTENDS SW FROM 32N138W TO WELL DEFINED 
CYCLONIC VORTEX AT 25N135W.  CYCLONE ATTRACTING ABUNDANT 
MOISTURE FROM HIGHER LATITUDES INTO NW CORNER OF E PAC ROTATING 
AROUND ITS CENTER.  BROAD ANTICYCLONIC GYRE DOWNSTREAM 
EFFECTIVELY COVER REMAINDER OF BASIN WITH E-W RIDGE ALONG 08N E 
OF 130W.  RIDGE CREST FLATTENED BY ANOTHER CYCLONE OVER FOUR 
CORNERS AREA IN SW CONUS.  PLENTY OF TROPICAL MOISTURE FROM ITCZ 
ADVECTING NE BY 90 KT JET CORE BETWEEN VORTEX AND GYRE.  
MODERATE MASS DIVERGENCE ALSO ENHANCES MODERATE CONVECTION ALONG 
ITCZ W OF 118W. 

RIDGE ALONG 08N PROVIDES GOOD OUTFLOW ABOVE ITCZ E OF 108W WITH 
SCATTERED DEEP CONVECTION MEETING FAVORABLE UPPER LEVEL 
ENVIRONMENT WITH VERY LOW WIND SHEAR.  GFS ONLY MODEL THAT FORMS 
WEAK LOW PRES NEAR 09N105W WITHIN 48 HRS...WHILE OTHER MODELS 
BARELY MAINTAIN WEAK TROUGH IN AREA.  GIVEN THE FAVORABLE 
CONDITIONS ALOFT...FORECAST WILL LEAN TOWARDS PLACING A WEAK 
TROUGH BUT WITHHOLD ANY TROPICAL SIGNS UNTIL MORE CERTAINTY IS 
AVAILABLE.
 
...AT THE SURFACE...
HIGH PRES 1023 MB AT 38N142W HAS RIDGE EXTEND TO 13N105W.  FRESH 
NW BREEZE WITHIN 180 NM OF BAJA CALIFORNIA W COAST DIMINISHES AS 
RIDGE BREAK DOWN AND DISSIPATES BY LATE FRI.  QUICKLY SUBSIDING 
CROSS-EQUATORIAL S-SW SWELLS STILL LINGER ACROSS MOST OF E PAC 
BASIN THROUGH SAT.  

WEAK TROUGH FROM 04N-10N ALONG 95W DISSIPATE FRI.  SECOND TROUGH 
DEVELOP FURTHER W WITH WEAK EMBEDDED LOW PRES NEAR 09N105W FRI 
THEN DRIFT W BEFORE DISSIPATING NEXT WEEK. 

$$
WALLY BARNES