000 WTPZ44 KNHC 070840 TCDEP4 TROPICAL STORM NARDA DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142013 200 AM PDT MON OCT 07 2013 RECENT MICROWAVE IMAGES INDICATE THAT NARDA HAS BEEN GETTING MORE ORGANIZED. A LONG CURVED BAND WRAPS AROUND THE WESTERN SIDE OF THE CIRCULATION AND CONNECTS TO AN INNER RING OF CONVECTION THAT IS OPEN TO THE NORTH OF THE CENTER. THE INITIAL INTENSITY IS RAISED TO 40 KT BASED ON DVORAK ESTIMATES OF T3.0/45 KT FROM TAFB AND T2.5/35 KT FROM SAB...AS WELL AS ADT AND AMSU ESTIMATES NEAR 40 KT. EASTERLY SHEAR IS GRADUALLY DIMINISHING AND SHOULD FALL BELOW 10 KT DURING THE NEXT 24 HOURS AS NARDA MOVES BENEATH AN UPPER-LEVEL RIDGE. OCEAN WATERS ARE PLENTY WARM AT AROUND 28C...AND THE STRUCTURE OF THE CYCLONE FAVORS CONTINUED STRENGTHENING FOR THE NEXT 2 TO 3 DAYS. GIVEN THESE FACTORS...THE NHC INTENSITY FORECAST GENERALLY FOLLOWS THE STATISTICAL MODELS...WHICH LIE AT THE UPPER RANGE OF THE GUIDANCE...AND SHOWS FASTER STRENGTHENING THAN INDICATED IN THE PREVIOUS ADVISORY FOR THE FIRST 48 HOURS. THEREAFTER...INCREASING VERTICAL SHEAR AND DRY STABLE AIR SHOULD CAUSE NARDA TO WEAKEN BY DAYS 4 AND 5. THE INITIAL MOTION IS 275/12 KT. NARDA IS LOCATED TO THE SOUTH OF A MID-LEVEL RIDGE THAT SHOULD STEER THE CYCLONE ON THIS TRAJECTORY FOR THE NEXT 36 HOURS OR SO. AFTER THAT TIME...THE STEERING PATTERN IS FORECAST TO COLLAPSE DUE TO A MID- TO UPPER-LEVEL TROUGH THAT WILL BE DIGGING SOUTHEASTWARD ACROSS THE U.S. WEST COAST...CAUSING NARDA TO SLOW TO A CRAWL BEGINNING IN 72 HOURS AND LASTING THROUGH THE END OF THE FORECAST PERIOD. THERE IS SOME SIGNIFICANT SPREAD AMONG THE TRACK GUIDANCE LATER IN THE PERIOD. THE GFS MAINTAINS A STRONGER CYCLONE THAT GETS PULLED NORTHWARD BY THE AMPLIFYING TROUGH WHILE THE ECMWF SHOWS A WEAKER SYSTEM BEING ADVECTED MORE QUICKLY TO THE WEST BY THE LOW-LEVEL FLOW. GIVEN THE UNCERTAINTY...THE NHC TRACK FORECAST SHOWS ONLY SLOW MOTION BETWEEN DAYS 3 THROUGH 5. THIS SOLUTION IS A LITTLE FASTER THAN THE MULTI-MODEL CONSENSUS TVCE AND VERY CLOSE TO THE NOAA FIM MODEL. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 13.2N 120.9W 40 KT 45 MPH 12H 07/1800Z 13.6N 122.6W 50 KT 60 MPH 24H 08/0600Z 14.2N 124.6W 60 KT 70 MPH 36H 08/1800Z 15.0N 126.5W 65 KT 75 MPH 48H 09/0600Z 15.5N 127.9W 70 KT 80 MPH 72H 10/0600Z 15.7N 129.2W 65 KT 75 MPH 96H 11/0600Z 15.8N 130.0W 50 KT 60 MPH 120H 12/0600Z 15.9N 130.9W 35 KT 40 MPH...POST-TROPICAL $$ FORECASTER BERG