000
AXPZ20 KNHC 292152
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
2205 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2115 UTC.

...SPECIAL FEATURE...
TROPICAL STORM HILARY AT 21.6N 120.7W AT 2100 UTC MOVING N-NW OR 
335 DEG AT 8 KT WITH CENTRAL PRES OF 1000 MB.  MAXIMUM SUSTAINED 
WIND 45 GUSTS TO 55 KT.  NUMEROUS MODERATE TO STRONG CONVECTION 
WITHIN 210 NM NE QUADRANT AND SCATTERED MODERATE CONVECTION 
ELSEWHERE WITHIN 75 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 15N93W TO 11N98W TO 11N103W TO 
09N108W TO 13N115W TO 10N136W THEN ITCZ FROM 10N136W TO BEYOND 
10N140W.  SCATTERED MODERATE ISOLATED STRONG CONVECTION WITHIN 
150 NM S OF TROUGH FROM 98W TO 105W.  SCATTERED MODERATE 
ISOLATED STRONG WITHIN 150 NM S OF TROUGH FROM 117W TO 121W. 

...DISCUSSION...
PREVIOUS UPPER LEVEL CYCLONIC CIRCULATION HAVE BECOME AN OPEN 
TROUGH FROM 32N123W TO 10N126W MOVING E. THIS INCREASES ITS 
SHEARING EFFECTS OVER HILARY...WHICH ALREADY FACES COOLER WATERS 
AND DRIER MORE STABLE AIR MASS TO ITS W...DOOMING IT TO BE 
LIKELY DEGRADED TONIGHT OR EARLY FRI.  

BROAD UPPER LEVEL RIDGE AXIS ALONG 15N E OF 125W HAS ILL-DEFINED 
GYRE AT 15N106W MAKING A FAVORABLE ENVIRONMENT FOR SURFACE LOW 
PRES CENTER 1009 MB AT 11N98W 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...
PREVIOUS HIGH PRES CENTER 1018 MB AT 25N147W DISSIPATED AS COLD 
FRONT ENTERS NW CORNER OF BASIN FROM 32N136W TO 28N140W.  FRONT  
BRINGS MODERATE TO FRESH BREEZE AND SEAS TO 8 FT NW OF FRONTAL 
BOUNDARY.  

STATIONARY LOW PRES CENTER 1010 MB AT 11N133W PRODUCES FRESH 
BREEZE WITHIN 90 NM OF ITS CENTER THROUGH 24 HRS THEN DIMINISHES 
TO MODERATE BREEZE.  UPPER LEVEL ENVIRONMENT NOT TOO FAVORABLE 
FOR TROPICAL DEVELOPMENT AND MODEL GUIDANCE WEAKENS IT WITHIN 48 
HRS.  
 
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 17 FT...PRESENTLY AFFECTING 
BAJA CALIFORNIA W COAST DIRECTLY AND TO A LESSER DEGREE THE REST 
OF THE W COAST OF MEXICO AND CENTRAL AMERICA. 

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

$$
WALLY BARNES