ZCZC MIATCDEP3 ALL TTAA00 KNHC DDHHMM HURRICANE MIRIAM DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132012 200 AM PDT MON SEP 24 2012 MIRIAM HAS CONTINUED TO RAPIDLY STRENGTHEN. A SMALL 10 N MI DIAMETER COULD-FILLED EYE IS EMBEDDED IN THE NORTHWEST QUADRANT OF A COLD CENTRAL DENSE OVERCAST FEATURE THAT HAS BECOME MORE CIRCULAR OVER THE PAST FEW HOURS. SATELLITE INTENSITY ESTIMATES ARE A CONSENSUS T5.0/90 KT FROM TAFB AND SAB...AND THE LATEST UW-CIMSS ESTIMATE IS T5.6/105 KT. BASED ON THESE DATA...THE INITIAL INTENSITY HAS BEEN INCREASED TO 90 KT...WHICH COULD BE ON THE CONSERVATIVE SIDE. THE INITIAL MOTION ESTIMATE 305/11 KT. MIRIAM IS BASICALLY ON TRACK...SO THERE IS NO CHANGE TO THE PREVIOUS FORECAST TRACK THROUGH 36 HOURS. AFTER THAT...HOWEVER...THE TRACK HAS BEEN SHIFTED TO THE EAST OF AND A LITTLE FASTER THAN THE PREVIOUS ADVISORY DUE TO MIRIAM FORECAST TO BE A DEEPER AND MORE ROBUST CYCLONE SIMILAR TO WHAT THE GFS AND ECMWF MODELS ARE INDICATING. THE UKMET MODEL WAS COMPLETELY DISCOUNTED SINCE IT WAS WAS POORLY INITIALIZED AND IS ONLY FORECASTING A VERY WEAK AND SHALLOW CYCLONE THAT DISSIPATES AND MOVES SLOWLY NORTHWEST AND WESTWARD WITH TIME...WHICH HAS RESULTED IN A DEGRADATION OF THE CONSENSUS MODELS TV15 AND TVCE. A BROAD MID-LEVEL TROUGH CURRENTLY ALONG THE U.S. WEST COAST IS FORECAST TO SLOWLY AMPLIFY SOUTHWARD OFF THE COAST OF BAJA CALIFORNIA AND CREATE A LARGE BREAK IN THE SUBTROPICAL RIDGE TO THE NORTH OF THE CYCLONE BY 48 HOURS. THIS CHANGING FLOW PATTERN IS EXPECTED TO GRADUALLY TURN MIRIAM NORTHWARD BY 72 HOURS...AND THEN RECURVE THE SYSTEM SLOWLY TO THE NORTHEAST TOWARD BAJA CALIFORNIA ON DAYS 4 AND 5. GIVEN THE PERSISTENT WEST BIAS OF THE UKMET... GFDL...AND HWRF MODELS...THE OFFICIAL FORECAST IS SIMILAR TO BUT SLOWER THAN A BLEND OF THE GFS...GFS-ENSEMBLE MEAN...AND ECMWF FORECAST TRACKS. GIVEN THE SMALL-DIAMETER EYE AND LOW SHEAR EXPECTED FOR THE NEXT 12 HOURS OR SO...ADDITIONAL RAPID STRENGTHENING INTO A MAJOR HURRICANE SEEMS HIGHLY PLAUSIBLE. IT IS POSSIBLE THAT MIRIAM COULD EVEN REACH CATEGORY 4 INTENSITY...BUT THE RATHER SMALL EYE COULD NEGATE THAT POSSIBILITY DUE TO A PROBABLE EYEWALL REPLACEMENT CYCLE SOMETIME DURING THE NEXT 24 HOURS. BY 36 HOURS AND BEYOND...MODERATE SOUTHWESTERLY SHEAR AHEAD OF THE AFOREMENTIONED MID-/UPPER-LEVEL TROUGH IS EXPECTED TO INDUCE GRADUAL WEAKENING. HOWEVER...THE WEAKENING TREND IS NOT EXPECTED TO BE AS FAST AS INDICATED IN PREVIOUS ADVISORIES NOW THAT MIRIAM IS FORECAST TO BE FARTHER EAST AND...THEREFORE...OVER WARMER SSTS. THE NHC INTENSITY FORECAST IS ABOVE ALL OF THE GUIDANCE FOR THE NEXT 24 HOURS...AND THEN FOLLOWS THE INTENSITY CONSENSUS MODELS TV15 AND IVCN. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 17.3N 112.2W 90 KT 105 MPH 12H 24/1800Z 18.0N 113.2W 105 KT 120 MPH 24H 25/0600Z 18.8N 114.3W 110 KT 125 MPH 36H 25/1800Z 19.6N 114.8W 100 KT 115 MPH 48H 26/0600Z 20.4N 115.2W 90 KT 105 MPH 72H 27/0600Z 22.2N 115.5W 75 KT 85 MPH 96H 28/0600Z 24.0N 115.5W 60 KT 70 MPH 120H 29/0600Z 25.5N 114.5W 50 KT 60 MPH $$ FORECASTER STEWART NNNN
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Page last modified: Monday, 31-Dec-2012 12:10:38 UTC