000
AXPZ20 KNHC 201522
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
1605 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1515 UTC.

...SPECIAL FEATURE...
TROPICAL STORM GREG NEAR 19.7N 120.0W AT 20/1500 UTC MOVING W AT 
09 KT. MAXIMUM SUSTAINED WINDS ARE 35 KT GUSTS TO 45 KT WITH AN 
ESTIMATED MINIMUM CENTRAL PRESSURE OF 1004 MB. GREG IS EXPECTED 
TO WEAKEN TO A TROPICAL DEPRESSION LATER TODAY AND BECOME A 
POST-TROPICAL REMNANT LOW BY TONIGHT. ALTHOUGH GREG CONTINUES TO 
SHOW GOOD ORGANIZATION THE DEEP CENTRAL CONVECTION HAS WARMED 
AND DECREASED IN AREAL COVERAGE. REFER TO FORECAST ADVISORIES 
ISSUED UNDER WMO HEADER WTPZ22 KNHC AND AWIPS HEADER MIATCMEP2 
FOR FURTHER DETAILS.

...ITCZ/MONSOON TROUGH...
MONSOON TROUGH INLAND ACROSS CENTRAL AMERICA THEN FROM 15N93W TO 
1008 MB LOW PRES NEAR 13N105W TO 10N110W RESUMES FROM 15N122W TO 
09N140W. SCATTERED MODERATE WITHIN 90 NM S OF TROUGH FROM 122W 
TO 129W. SCATTERED MODERATE TO ISOLATED STRONG WITHIN 75 NM SE 
OF LINE FROM 17N117W TO 15N120W. SIMILAR CONVECTION IS ALSO 
NOTED FROM 10N TO 15N BETWEEN 103W AND 110W. CLUSTER OF MODERATE 
TO STRONG CONVECTION OVER THE GULF OF TEHUANTEPEC AND WITHIN 120 
NM S OF MONSOON TROUGH FROM 93W TO 96W.

...DISCUSSION...
TROPICAL STORM GREG IS SLOWLY WEAKENING AS IT TRAVERSES COOLER 
WATERS. A MUCH EARLIER SCATTEROMETER PASS DIRECTLY OVER THE 
CENTER SHOWED 35-40 KT WINDS NEAR THE CENTER WITH HIGHEST WINDS 
IN THE N SEMICIRCLE. SINCE THEN THE DEEP CONVECTION HAS CONTINUED
TO DECREASE IN COVERAGE EXTENDING OUT TO ONLY 45 NM WITHIN THE S 
AND 30 NM IN THE N SEMICIRCLES SUGGESTING WINDS ARE MARGINALLY 
TROPICAL STORM FORCE. GLOBAL MODEL GUIDANCE DEPICTS A TAIL OF SW 
WINDS OF 20-25 KT AND ENHANCED SEAS EXTENDING S AND SE OF THE 
CENTER THROUGH SUN WHICH APPEARS LIKELY GIVEN THE EMBEDDED SW 
MONSOON FLOW ALREADY IN PLACE. EXPECT GREG TO DISSIPATE 
COMPLETELY WITHIN 72 HOURS WITH THE LOW LEVEL CENTER EVENTUALLY 
BEING ABSORBED IN THE LARGER SCALE CYCLONIC MONSOON CIRCULATION 
ACROSS THE REGION.

THE LOW PRES NEAR 13N105W SHOWS SOME CYCLONIC TURNING IN FIRST 
VISIBLE SATELLITE IMAGES OF THE DAY. THE LOW IS EXPECTED TO 
REMAIN EMBEDDED IN THE MONSOON TROUGH AS THE TROUGH GRADUALLY 
LIFTS NORTHWARD THROUGH MON. SW WINDS OF 20-25 KT WITH SEAS TO 9 
FT ASSOCIATED WITH THIS LOW IN THE MONSOON TROUGH THROUGH MON.

ANOTHER WEAK AREA OF LOW PRESSURE WAS ALSO EMBEDDED WITHIN THE 
MONSOON TROUGH IN THE GULF OF TEHUANTEPEC NEAR 15.5N94W. THIS 
LOW IS EXPECTED TO REMAIN STATIONARY IN THE AREA THROUGH SUN 
WITH MINIMAL IMPACTS ON THE WINDS AND SEAS IN THE AREA.  

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. LONG PERIOD CROSS EQUATORIAL 
SWELLS OF 15-17 SEC WILL PUSH NORTHWARD ACROSS THE EAST PACIFIC 
E OF 115W WITH SEAS REMAINING NEAR 8 FT NEAR THE EQUATOR.

$$
COBB