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Tropical Storm NARDA Forecast Discussion Number 4
2013-10-07 16:46:01| National Hurricane Center (East Pacific)
Issued at 800 AM PDT MON OCT 07 2013 000 WTPZ44 KNHC 071445 TCDEP4 TROPICAL STORM NARDA DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142013 800 AM PDT MON OCT 07 2013 NARDA HAS BEEN INTENSIFYING...WITH A LONG CURVED CONVECTIVE BAND WRAPPING AROUND MOST OF THE CIRCULATION. MICROWAVE IMAGERY SHOWS A POSSIBLE PARTIAL EYEWALL BUT WITH SOME SEPARATION BETWEEN THE LOW- AND MID-LEVEL CENTERS. DVORAK INTENSITY ESTIMATES AT 1200 UTC ARE 45 AND 55 KT FROM SAB AND TAFB...RESPECTIVELY. BASED ON SOME FURTHER INCREASE IN ORGANIZATION SINCE THAT TIME...THE HIGHER OF THE TWO DVORAK ESTIMATES IS SELECTED FOR THIS ADVISORY. RECENT FIXES SUGGEST THAT THE CENTER WAS FARTHER NORTH THAN PREVIOUSLY INDICATED...AND A LONG-TERM MOTION ESTIMATE IS 285/13. NARDA SHOULD BE STEERED WEST-NORTHWESTWARD UNDER THE WESTERN SIDE OF A MID-LEVEL RIDGE OVER NORTHERN MEXICO. AS AN AMPLIFIED MID- TO UPPER-LEVEL TROUGH DIGS NEAR THE U.S. WEST COAST IN A FEW DAYS...THE CYCLONE SHOULD SLOW DOWN AND TURN NORTHWESTWARD. THE ECMWF SHOWS A WEAKER SYSTEM SUCCUMBING TO SHEAR AND TURNING WESTWARD SOONER THAN THE REST OF THE GUIDANCE...WHEREAS THE GFS PREDICTS A DEEPER SYSTEM GAINING MORE LATITUDE BEFORE WEAKENING AND TURNING WESTWARD. THE NHC OFFICIAL TRACK IS ADJUSTED TO THE RIGHT TO ACCOUNT FOR THE INITIAL NORTHWARD RELOCATION AND TO BE CLOSER TO THE MULTI-MODEL CONSENSUS...WHICH ASSUMES A DEEPER CYCLONE THAN FORECAST BY THE ECMWF. NARDA SHOULD BE MOVING OVER WARM BUT GRADUALLY DECREASING SEA SURFACE TEMPERATURES AND PASSING UNDERNEATH AN UPPER-LEVEL RIDGE AXIS DURING THE NEXT 24-36 HOURS. THIS ENVIRONMENT SHOULD ALLOW NARDA TO STRENGTHEN INTO A HURRICANE SOON. IN ABOUT TWO DAYS...WESTERLY VERTICAL SHEAR WILL INCREASE AND SHOULD BECOME EVEN STRONGER BY THE END OF THE FORECAST PERIOD WHILE NARDA TRAVERSES COOLER WATERS. THIS SHOULD LEAD TO RAPID WEAKENING BY DAY 4...AND NARDA IS FORECAST TO BECOME POST-TROPICAL BY DAY 5. THE NHC INTENSITY FORECAST IS RAISED OVER THE PREVIOUS ONE BASED ON CURRENT TRENDS AND IS A LITTLE ABOVE THE GUIDANCE IN THE SHORT TERM. WHILE THE INTENSITY PREDICTION IS UNCHANGED AT LONG RANGE...IT IS VERY SENSITIVE TO THE TRACK FORECAST...WITH A DEEPER/STRONGER CYCLONE LIKELY MOVING FARTHER NORTH AND EXPERIENCING THE EFFECTS OF SHEAR SOONER. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 14.0N 122.5W 55 KT 65 MPH 12H 08/0000Z 14.4N 124.2W 60 KT 70 MPH 24H 08/1200Z 15.1N 126.4W 70 KT 80 MPH 36H 09/0000Z 15.6N 127.9W 75 KT 85 MPH 48H 09/1200Z 16.1N 128.9W 70 KT 80 MPH 72H 10/1200Z 16.5N 129.5W 60 KT 70 MPH 96H 11/1200Z 16.7N 130.4W 45 KT 50 MPH 120H 12/1200Z 16.7N 132.0W 30 KT 35 MPH...POST-TROPICAL $$ FORECASTER KIMBERLAIN
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