000
AXPZ20 KNHC 291558
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC THU SEP 29 2011

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM 
THE EQUATOR TO 32N...EAST OF 140W. THE FOLLOWING INFORMATION IS 
BASED ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND 
METEOROLOGICAL ANALYSIS.

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1515 UTC.

...SPECIAL FEATURE...
TROPICAL STORM HILARY AT 20.4N120.3W AT 1500 UTC MOVING NW OR 
325 DEG AT 6 KT WITH INCREASING CENTRAL PRES OF 1003 MB.  
MAXIMUM SUSTAINED WIND 40 GUSTS TO 50 KT.  NUMEROUS MODERATE 
ISOLATED STRONG CONVECTION WITHIN 180 NM NE QUADRANT OF CENTER 
AND ISOLATED TO SCATTERED MODERATE CONVECTION ELSEWHERE WITHIN 
90 NM OF CENTER.  HILARY WEAKENING QUICKLY...AS COOL WATERS AND 
VERTICAL WIND SHEAR ADVERSELY IMPACT STORM ORGANIZATION...WITH 
COOLER STABLE LOW LEVEL CIRCULATION DECOUPLED FROM ITS SHEARED 
MID LEVEL.  THIS ENVIRONMENT EXPECTED TO FURTHER WEAKEN HILARY 
TO EXTINCTION BY THE WEEKEND.  SWELLS GENERATED BY HILARY 
CONTINUE TO AFFECT W COAST OF BAJA CALIFORNIA...SOUTHERN GULF OF 
CALIFORNIA...AND ADJACENT PORTIONS OF SW MEXICO...CAUSING HIGH 
SURF AND LIFE-THREATENING RIP CURRENT CONDITIONS.  SEE LATEST 
NHC FORECAST/ ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP4/WTPZ24 
KNHC FOR MORE DETAILS. 
 
...ITCZ/MONSOON TROUGH...
MONSOON TROUGH AXIS EXTENDS FROM NW COSTA RICA TO 14N93W TO 1009 
MB LOW PRES AT 11N99W ENDING WITH 1009 MB LOW PRES AT 08N108W. 
AXIS THEN RESUMES FROM 1010 MB LOW PRES AT 11N133W TO 10N140W.   
SCATTERED MODERATE TO STRONG WITHIN 90 NM S OF AXIS FROM 85W TO 
88W.  ISOLATED MODERATE CONVECTION WITHIN 60 NM S OF AXIS FROM 
110W TO 120W. 

...DISCUSSION...
UPPER LEVEL CYCLONIC CIRCULATION AT 28N126W WEAKENS INTO AN OPEN 
TROUGH TODAY AND MOVES E INCREASING ITS SHEARING EFFECTS AND 
SPELLING DOOM FOR HILARY...WHICH ALREADY FACES COOLER WATERS AND 
DRIER MORE STABLE AIR MASS TO ITS W. 

BROAD UPPER LEVEL RIDGE AXIS ALONG 14N E OF 120W HAS A DOUBLE 
BARREL STRUCTURE WITH ONE ILL-DEFINED GYRE NEAR 13N106W AND 
ANOTHER NEAR 15N96W.  THESE GYRES MAKE FAVORABLE ENVIRONMENT FOR 
SURFACE LOW PRES CENTER 1009 MB AT 11N99W ENHANCING ITS 
CONVECTION WITH MASS DIVERGENCE ALOFT.  MODEL GUIDANCE MAINTAIN 
CIRCULATION DURING NEXT TWO DAYS THEN WEAKEN IT AS IT CONTINUES 
DRIFTING W AND ENTER MORE ADVERSE CONDITIONS.  

...ELSEWHERE AT THE LOWER LEVELS...
VERY WEAK HIGH PRES CENTER 1018 MB AT 25N147W WITH RIDGE 
EXTENDING INTO E PAC W OF 133W DISSIPATE BY TONIGHT AS COLD 
FRONT ENTERS NW CORNER OF BASIN.  FRONT BRINGS MODERATE TO FRESH 
BREEZE AND SEAS TO 8 FT NW OF ITS BOUNDARY.  

WEAKENING LOW PRES CENTER 1010 MB AT 11N133W PRODUCES FRESH 
BREEZE WITHIN 90 NM OF ITS CENTER THROUGH 24 HRS THEN DIMINISHES 
TO MODERATE BREEZE.  ALTHOUGH ENVIRONMENT IS NOT FAVORABLE FOR 
ANY TROPICAL DEVELOPMENT MODEL GUIDANCE MAINTAINS STRUCTURE... 
BUT DIVERSITY OF TRACK SOLUTIONS MAKES FORECAST UNCERTAIN.  
 
LONG PERIOD SWELL TRAINS DUE TO SEVERAL DIFFERENT SOURCES MAKE 
CONFUSED SEAS THE NORM FOR LARGE PORTIONS OF E PAC.  HIGHEST 
ONES...MAINLY FROM HILARY AS HIGH AS 18 FT...PRESENTLY AFFECTING 
BAJA CALIFORNIA W COAST DIRECTLY AND TO A LESSER DEGREE REST OF 
COAST OF MEXICO. 

HIGH PRES CENTER 1014 MB BUILDING STRONGER OVER GULF OF MEXICO 
INDUCE STRONG WINDS ACROSS CHIVELAS PASS SEEPING INTO GULF OF 
TEHUANTEPEC BY LATE FRI.  MODEL GUIDANCE SOLUTIONS INDICATE WIND 
AS STRONG AS NEAR GALE FORCE.   

$$
WALLY BARNES