000
WTPZ42 KNHC 180236
TCDEP2
 
HURRICANE GREG DISCUSSION NUMBER   6
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP072011
800 PM PDT WED AUG 17 2011
 
LATE AFTERNOON VISIBLE SATELLITE IMAGES SHOWED A BANDING EYE
FEATURE THAT BECAME OBSCURED AS NEW CONVECTION DEVELOPED NEAR
THE CENTER AROUND SUNSET.  THE SMALL EYE FEATURE WAS ALSO EVIDENT
IN A 2025 UTC TRMM OVERPASS.  UNFORTUNATELY...THERE HAS BEEN NO
ADDITIONAL MICROWAVE IMAGERY SINCE THAT TIME.  ALTHOUGH DVORAK FINAL
T-NUMBERS FROM TAFB AND SAB WERE 4.0 AND 3.5...RESPECTIVELY...THE
DATA T-NUMBERS FROM BOTH AGENCIES WERE 4.0.  THIS SUPPORTS
INCREASING THE WIND SPEED TO 65 KT.  GREG BECOMES THE SIXTH
HURRICANE IN THE EASTERN PACIFIC BASIN IN 2011.
 
SEA SURFACE TEMPERATURES ALONG THE PATH OF GREG GRADUALLY COOL
THROUGHOUT THE FORECAST PERIOD...HOWEVER THE CYCLONE IS FORECAST
TO REMAIN OVER 27-28 DEGREE CELSIUS WATER FOR ANOTHER 24 HOURS OR
SO.  DURING THAT TIME...SHEAR IS EXPECTED TO REMAIN LIGHT WHICH
SHOULD ALLOW FOR ADDITIONAL STRENGTHENING.  THE UPDATED FORECAST
INDICATES A PEAK INTENSITY OF 85 KT IN 24 HOURS AND IS IN BEST
AGREEMENT WITH THE SHIPS/LGEM GUIDANCE.  THEREAFTER...STEADY
WEAKENING IS SHOWN AS GREG IS FORECAST TO MOVE OVER DECREASING
SSTS.
 
THE INITIAL MOTION REMAINS A BRISK 285/19.  GREG CONTINUES TO BE
STEERED QUICKLY WEST-NORTHWESTWARD BETWEEN A LARGE MID/UPPER-LEVEL
RIDGE OVER THE SOUTHERN UNITED STATES AND A CYCLONIC GYRE TO THE
SOUTHWEST OF THE CYCLONE.  AS THE GYRE WEAKENS DURING THE NEXT 24
HOURS...GREG SHOULD TURN WESTWARD AND SLOW DOWN.  THE WESTERN
PORTION OF THE RIDGE IS FORECAST TO WEAKEN IN A COUPLE OF DAYS AS A
TROUGH APPROACHES THE WEST COAST OF THE UNITED STATES.  THIS SHOULD
RESULT IN A FURTHER REDUCTION OF FORWARD SPEED.  THE MODELS ARE IN
GOOD AGREEMENT ON THIS SCENARIO...BUT THE LATEST GUIDANCE ENVELOPE
HAS SHIFTED SOUTHWARD AT 72 HOURS AND BEYOND.  THIS REQUIRES A
SOUTHWARD ADJUSTMENT TO THE TRACK IN THE LATTER PORTION OF THE
FORECAST PERIOD.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/0300Z 17.5N 108.3W   65 KT  75 MPH
 12H  18/1200Z 18.1N 110.8W   75 KT  85 MPH
 24H  19/0000Z 18.6N 113.4W   85 KT 100 MPH
 36H  19/1200Z 18.9N 115.4W   75 KT  85 MPH
 48H  20/0000Z 19.0N 117.5W   65 KT  75 MPH
 72H  21/0000Z 19.0N 120.0W   50 KT  60 MPH
 96H  22/0000Z 19.0N 122.5W   35 KT  40 MPH
120H  23/0000Z 19.0N 124.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
FORECASTER BROWN