000
AXPZ20 KNHC 200345
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC SAT AUG 20 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0300 UTC.

...SPECIAL FEATURE...
TROPICAL STORM GREG CONTINUES TO WEAKEN OVER COOLER WATERS.  AT 
20/0300 UTC AT 19.6N 117.0W MOVING W AT 10 KT.  MAXIMUM WIND 45 
GUSTS TO 60 KT.  WEAKENING FORECAST THROUGHPUT NEXT 48 HOURS AND 
EXPECTED TO BECOME POST-TROPICAL REMNANT LOW PRES SUN.  MINIMUM 
CENTRAL PRES 994 MB.  DEEP CONVECTION SURROUNDING CENTER HAS 
DECREASED SUBSTANTIALLY WITH SMALL AREA OF MODERATE CONVECTION 
WITHIN 30 NM OF CENTER.  REFER TO FORECAST ADVISORIES ISSUED 
UNDER WMO HEADER WTPZ22 KNHC AND AWIPS HEADER MIATCMEP2 FOR 
FURTHER DETAILS.

...ITCZ/MONSOON TROUGH...
MONSOON TROUGH FROM 11N86W TO 1010 MB LOW PRES AT 11N103W THEN 
FROM 16N120W TO 11N134W TO 11N140W.  SCATTERED MODERATE 
CONVECTION WITHIN 150 NM S OF AXIS FROM 120W TO 127W AND FROM 
06N TO 10N BETWEEN 83W AND 89W.

...DISCUSSION...
SHARP LARGE AMPLITUDE UPPER LEVEL TROUGH EXTEND FROM 32N130W TO 
ILL-DEFINED CYCLONE AT 19N118W JUST W OF T.S. GREG.   LARGE 
ANTICYCLONE ANCHORED AT 21N136W HAS VERY DRY AIR MASS COVER MOST 
OF REGION N OF 17N W OF 120W.  SECOND LARGE ANTICYCLONE CENTERED 
OVER WESTERN TEXAS CONTROLS FLOW ACROSS REMAINDER E PAC E OF 
120W.  

...AT THE LOWER LEVELS...
HEALTHY SURFACE HIGH PRES CENTER 1028 MB WELL N OF BASIN BLOCK 
ANY FURTHER MOVEMENT N DISPLACEMENT OF GREG.  COOLER WATERS HAS 
WEAKENED GREG AND IT IS EXPECTED TO LOSE MOST OF ITS CONVECTION 
WITHIN THE NEXT TWO DAYS.  

WIND AND SEAS ASSOCIATED WITH MONSOON TROUGH SET A SWATH OF 
STRONG SW WINDS EXTENDING SE OF GREG FROM 12N123W TO 17N117W.
WINDS COINCIDE WITH BAND OF CONVECTION ALONG MONSOON TROUGH AND 
IS EXPECTED TO DIMINISH BY SUN. 

LOW PRES AREA 1010 MB AT 12N103W ASSOCIATED WITH LARGE AREA OF 
MODERATE TO STRONG CONVECTION.  ANTICYCLONIC UPPER LEVEL 
ENVIRONMENT NOT UNFAVORABLE WHILE MONSOONAL TROUGH COULD ENHANCE 
LOW LEVEL CONVERGENCE OF WARM MOIST AIR MASS.  SOME GRADUAL 
DEVELOPMENT IS POSSIBLE OVER NEXT DAYS AS IT DRIFT W INTO MORE 
HOSTILE ENVIRONMENT. 

$$
WALLY BARNES