000
WTPZ42 KNHC 210233
TCDEP2
 
TROPICAL DEPRESSION GREG DISCUSSION NUMBER  18
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP072011
800 PM PDT SAT AUG 20 2011
 
A SMALL AREA OF DEEP CONVECTION HAS PERSISTED ON THE NORTHEASTERN
EDGE OF THE CENTER OF GREG OVER THE PAST 12 HOURS. SATELLITE CURRENT
INTENSITY ESTIMATES ARE 35 AND 30 KT FROM TAFB AND SAB...
RESPECTIVELY...WHILE BOTH AGENCIES REPORTED A FINAL T-NUMBER
INTENSITY OF 25 KT. THE INITIAL INTENSITY OF 30 KT IS AN AVERAGE OF
THE DVORAK NUMBERS...AND GREG IS DOWNGRADED TO A TROPICAL
DEPRESSION ON THIS ADVISORY.
 
THE INITIAL MOTION IS 285/06. GREG WILL BE STEERED ON A
WEST-NORTHWEST TRACK TONIGHT BY THE NORTHEAST PACIFIC SUBTROPICAL
HIGH AND ITS ASSOCIATED SURFACE RIDGE. THE SURFACE RIDGE IS
WEAKENING AS A MID- TO UPPER-LEVEL TROUGH DIGS OFF THE WEST COAST...
WHICH WILL LIKELY ALLOW GREG TO DRIFT SLIGHTLY FARTHER NORTH THAN
EARLIER ANTICIPATED. AS GREG WEAKENS AND BECOMES INCREASINGLY
SHALLOW IT SHOULD BE STEERED TOWARD THE WEST BY THE SURFACE RIDGE
ON SUNDAY AND THEN TOWARD THE WEST-SOUTHWEST SUNDAY NIGHT AND
MONDAY. THE FORECAST TRACK HAS BEEN NUDGED TO THE NORTH AGAIN AND
IS ESSENTIALLY DOWN THE MIDDLE OF THE GUIDANCE ENVELOPE.
 
GREG WILL CONTINUE WEAKENING OVER COOL WATERS. SSTS WILL REMAIN IN
THE RATHER COLD 22C TO 23C RANGE DURING THE NEXT COUPLE OF DAYS...
AND STABLE AIR WILL CONTINUE TO BE INGESTED FROM THE NORTH. AS A
RESULT...GREG IS FORECAST TO SPIN DOWN TO A REMNANT LOW PRESSURE
SYSTEM ON SUNDAY.

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/0300Z 20.1N 121.0W   30 KT  35 MPH
 12H  21/1200Z 20.2N 122.0W   25 KT  30 MPH
 24H  22/0000Z 20.1N 123.4W   25 KT  30 MPH...POST-TROP/REMNT LOW
 36H  22/1200Z 19.6N 124.9W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  23/0000Z 19.0N 126.3W   20 KT  25 MPH...POST-TROP/REMNT LOW
 72H  24/0000Z...DISSIPATED
 
$$
FORECASTER WROE/BRENNAN