000
WTPZ43 KNHC 240242
TCDEP3
 
HURRICANE MIRIAM DISCUSSION NUMBER   9
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP132012
800 PM PDT SUN SEP 23 2012
 
MIRIAM HAS STRENGTHENED RAPIDLY DURING THE LAST 6 HOURS OR SO. AN
EYE...WHICH HAD BEEN EVIDENT IN MICROWAVE DATA EARLIER TODAY...
BECAME APPARENT IN GEOSTATIONARY SATELLITE IMAGES A FEW HOURS AGO.
THE OVERALL CLOUD PATTERN IS WELL ORGANIZED WITH COLD CLOUD TOPS
SURROUNDING THE RAGGED EYE AND BANDING FEATURES LOCATED IN ALL
QUADRANTS. SATELLITE INTENSITY ESTIMATES HAVE INCREASED TO 4.0/65
KT FROM TAFB...4.5/77 KT FROM SAB...AND 4.7/82 KT FROM UW-CIMSS.
THE INITIAL WIND SPEED IS SET AT 80 KT...NEAR THE HIGH END OF THE
ESTIMATES GIVEN THE IMPROVED SATELLITE PRESENTATION SINCE THE TIME
OF THE DVORAK CLASSIFICATIONS.
 
ADDITIONAL STRENGTHENING SEEMS LIKELY DURING THE NEXT DAY OR SO AS
MIRIAM IS EXPECTED TO REMAIN OVER SEA SURFACE TEMPERATURES OF
27-28C AND IN A FAVORABLE UPPER-LEVEL WIND PATTERN. IN 36 TO 48
HOURS...HOWEVER...MIRIAM IS FORECAST TO BE MOVING OVER COOL WATERS
AND IN MODERATE SOUTHWESTERLY WIND SHEAR. THESE UNFAVORABLE
CONDITIONS SHOULD END THE STRENGTHENING TREND...AND CAUSE THE
CYCLONE TO WEAKEN. THE NHC INTENSITY FORECAST IS HIGHER THAN THE
PREVIOUS ONE FOR THE FIRST 36 HOURS AND THEN FALLS IN LINE WITH THE
OLD ONE AFTER THAT.
 
MIRIAM IS MOVING NORTHWESTWARD AT ABOUT 10 KT. THIS GENERAL HEADING
WITH A SLIGHT REDUCTION IN FORWARD SPEED IS EXPECTED OVER THE NEXT
24 TO 36 HOURS AS THE RIDGE TO THE NORTHEAST OF MIRIAM WEAKENS.
AFTER THAT...A TURN TO THE NORTH AT AN EVEN SLOWER FORWARD SPEED IS
FORECAST AS THE HURRICANE MOVES INTO A WEAKNESS CAUSED BY A TROUGH
OVER THE WESTERN UNITED STATES. THE NHC TRACK FORECAST IS BASICALLY
AN UPDATE OF THE PREVIOUS ONE...AND REMAINS NEAR THE RIGHT SIDE OF
THE GUIDANCE ENVELOPE BETWEEN THE CONSENSUS AIDS TO THE WEST AND
THE GFS AND ECMWF MODELS TO THE EAST.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  24/0300Z 16.8N 111.3W   80 KT  90 MPH
 12H  24/1200Z 17.6N 112.5W   95 KT 110 MPH
 24H  25/0000Z 18.5N 113.9W   95 KT 110 MPH
 36H  25/1200Z 19.2N 114.8W   90 KT 105 MPH
 48H  26/0000Z 19.8N 115.2W   80 KT  90 MPH
 72H  27/0000Z 21.2N 115.9W   60 KT  70 MPH
 96H  28/0000Z 22.5N 116.0W   45 KT  50 MPH
120H  29/0000Z 24.0N 115.5W   30 KT  35 MPH
 
$$
FORECASTER CANGIALOSI