000 WTPZ42 KNHC 230850 TCDEP2 TROPICAL STORM NORA DISCUSSION NUMBER 2 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP172009 200 AM PDT WED SEP 23 2009 DURING THE PAST SEVERAL HOURS...THE SYSTEM HAS BEEN TRANSITIONING FROM A BLOB OF CENTRAL CONVECTION ON SATELLITE IMAGERY TO A SPIRAL BANDING PATTERN...RESULTING IN A MORE ORGANIZED APPEARANCE. A QUIKSCAT PASS AT 0218 UTC SUGGESTED THE MAXIMUM WINDS WERE AT LEAST 30 KT AND AN ASCAT PASS AT 0537 UTC GENERALLY SHOWED STRONGER WINDS THROUGHOUT THE CIRCULATION THAN THE QUIKSCAT...BUT STILL SHOWED A PEAK WIND SPEED OF ABOUT 30 KT. DVORAK SATELLITE ESTIMATES FROM TAFB/SAB WERE 35 AND 30 KT...RESPECTIVELY...AT 0600 UTC...WITH AMSU ESTIMATES OF ABOUT 40-45 KT. AFTER CONSIDERING THE IMPROVED SATELLITE APPEARANCE AND GENERAL LOW BIAS OF ASCAT...THE INITIAL INTENSITY WILL BE SET TO 35 KT. NORA APPEARS TO HAVE ABOUT 24-36 HOURS TO STRENGTHEN BEFORE SHEAR INCREASES FROM THE SOUTHWEST OR WEST DUE TO A LARGE EASTERN PACIFIC TROUGH. THE REGIONAL HURRICANE MODELS...HWRF/GFDL... CONTINUE TO INTENSIFY THE CYCLONE MORE THAN THE STATISTICAL GUIDANCE...WITH THE HWRF MAKING NORA A HURRICANE BY TOMORROW. IT IS WORTH POINTING OUT THAT THE SHIPS RAPID INTENSIFICATION INDEX DOES SHOW A 25 PERCENT CHANCE OF A 30 KT INCREASE DURING THE NEXT 24 HOURS...WHICH IS ABOUT 3 TIMES THE SAMPLE MEAN. THE OFFICIAL FORECAST IS INCREASED FROM THE PREVIOUS FORECAST BUT REMAINS CLOSER TO THE STATISTICAL GUIDANCE AT THIS TIME. IN THE LONGER-TERM... THE HWRF/GFDL PROBABLY SHOW TOO STRONG OF A SYSTEM IN A SHEARED ENVIRONMENT...A COMMON BIAS OF THOSE MODELS. COOLER WATERS AND STRONG SHEAR SHOULD PROMOTE WEAKENING OF NORA INTO A REMNANT LOW IN ABOUT 3 DAYS. A SERIES OF MICROWAVE PASSES OVERNIGHT HAS HELPED SET THE INITIAL MOTION TO 310/7...THOUGH THE RECENT ASCAT DATA SUGGEST THE CENTER COULD BE MOVING A LITTLE MORE TO THE LEFT. A MIDDLE TO UPPER-LEVEL RIDGE TO THE NORTH IS STEERING THE CYCLONE FOR THE TIME BEING. THERE IS A FAIR AMOUNT OF MODEL DISAGREEMENT ON WHETHER THE RIDGE BUILDS WESTWARD...CAUSING A MORE WESTWARD TRACK OF NORA...OR IF THE MID- TO UPPER-LEVEL TROUGH CURRENTLY OVER THE EASTERN PACIFIC CAUSES A BREAK IN THE RIDGE...WHICH WOULD ALLOW THE CURRENT NORTHWESTWARD MOTION TO CONTINUE. THE GFS/GFDL/ECMWF/HWRF GENERALLY FAVOR A WEST OR WEST-NORTHWEST TRACK FOR THE NEXT FEW DAYS... WHILE THE NOGAPS AND CANADIAN MODELS SUPPORT A NORTHWESTWARD MOTION. MY INCLINATION IS TO LEAN TOWARD THE MORE EQUATORWARD SOLUTION AS THIS SYSTEM SEEMS UNLIKELY TO GET STRONG ENOUGH TO FEEL THE FULL EFFECTS OF THAT TROUGH. THE OFFICIAL FORECAST IS SHIFTED TO THE LEFT...BUT IS NOT AS FAR LEFT AS THE MODEL CONSENSUS DUE TO CONTINUITY CONSIDERATIONS. IT WOULD NOT BE SURPRISING IF THE FORECAST SHIFTED FARTHER WESTWARD LATER TODAY. IN A FEW DAYS...A MORE SIGNIFICANT BREAK IN THE RIDGE COULD ALLOW THE SYSTEM TO GAIN LATITUDE. HOWEVER...IT IS EXPECTED THAT THE CYCLONE WILL BE QUITE WEAK BY THAT TIME AND UNABLE TO RESPOND TO THAT STEERING FLOW. FORECAST POSITIONS AND MAX WINDS INITIAL 23/0900Z 16.1N 116.7W 35 KT 12HR VT 23/1800Z 16.6N 117.5W 45 KT 24HR VT 24/0600Z 17.0N 118.4W 50 KT 36HR VT 24/1800Z 17.2N 119.4W 45 KT 48HR VT 25/0600Z 17.4N 120.6W 35 KT 72HR VT 26/0600Z 17.7N 123.0W 25 KT...REMNANT LOW 96HR VT 27/0600Z 18.0N 125.5W 20 KT...REMNANT LOW 120HR VT 28/0600Z...DISSIPATED $$ FORECASTER BLAKE