000
AXPZ20 KNHC 201021
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0900 UTC.

...SPECIAL FEATURE...
TROPICAL STORM GREG NEAR 19.7N 119.0W AT 20/0900 UTC MOVING W AT 
09 KT. MAXIMUM WIND 40 GUSTS TO 50 KT. GREG IS EXPECTED TO WEAKEN
AND BECOME A POST-TROPICAL REMNANT LOW BY SAT NIGHT. DEEP CENTRAL
CONVECTION HAS WARMED...BUT CONTINUES TO SHOW GOOD ORGANIZATION. 
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 14N95W TO 1008 MB LOW PRES NEAR 
12N102W TO 10N109W RESUMES FROM 15N120W TO 11N132W TO 10N140W. 
SCATTERED MODERATE CONVECTION WITHIN 60 NM SW OF TROUGH FROM 
117W TO 130W AND WITHIN 150 NM OF TROUGH FROM 09N TO 15N BETWEEN 
88W AND 105W.

...DISCUSSION...
TROPICAL STORM GREG IS SLOWLY WEAKENING. A SCATTEROMETER PASS 
DIRECTLY OVER THE CENTER AT 0536 UTC SHOWED 35-40 KT WINDS NEAR 
THE CENTER WITH HIGHEST WINDS IN THE N SEMICIRCLE. THIS SCAT PASS
WAS PRIMARY BASIS FOR WINDS...AND TO A LESSER EXTENT...THE SEAS 
AROUND T.S. GREG. MODEL GUIDANCE DEPICTS A TAIL OF HIGHER WINDS 
AND SEAS EXTENDING S AND SE OF THE CENTER...WHICH APPEARS LIKELY 
GIVEN THE EMBEDDED SW MONSOON FLOW ALREADY IN PLACE. EXPECT GREG 
TO DISSIPATE COMPLETELY WITHIN 48-72 HOURS WITH THE LOW LEVEL 
EVENTUALLY BEING ABSORBED IN THE LARGER SCALE CYCLONIC MONSOON 
CIRCULATION ACROSS THE REGION.

THE LOW PRES NEAR 12N102W HAS WEAK CYCLONIC CIRCULATION FROM IR 
ANIMATED IMAGERY AND MAY INTENSIFY SLIGHTLY OVER THE NEXT COUPLE 
OF DAYS. BUT GFS MODEL GUIDANCE SHOWS THE LOW REMAINING EMBEDDED 
IN THE MONSOON TROUGH AS THE TROUGH GRADUALLY LIFTS NORTHWARD 
THIS WEEKEND WITH LITTLE DEVELOPMENT BEYOND 25-30 EXPECTED. COULD
SEE AN INCREASE IN SW WINDS AND SEAS ASSOCIATED WITH THIS LOW IN 
THE MONSOON TROUGH THROUGH MON.

OTHERWISE VERY LITTLE OF NOTE ACROSS THE DISCUSSION AREA. WINDS 
WILL INCREASE TO 15-20 KT ALONG THE NORTHERN BAJA PENINSULA... 
PUSHING SEAS TO 6-7 FT BY MON. CROSS EQUATORIAL SWELL HAVE ONLY 
A MINOR EFFECT WITH SEAS REMAINING BELOW 8 FT NEAR THE EQUATOR.

$$
MUNDELL