000 WTNT42 KNHC 060837 TCDAT2 SUBTROPICAL DEPRESSION SEVENTEEN DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL172010 500 AM AST WED OCT 06 2010 SATELLITE IMAGES INDICATE THAT THE AREA OF LOW PRESSURE NORTH OF PUERTO RICO HAS DEVELOPED BANDS OF DEEP AND CURVED CONVECTION IN THE NORTHERN AND EASTERN QUADRANTS. IN ADDITION...NIGHT VISIBLE IMAGES SUGGEST THAT THE CENTER HAS BECOME BETTER-DEFINED SINCE YESTERDAY. SATELLITE CLASSIFICATIONS ARE A TROPICAL 2.0 FROM TAFB...AND A SUBTROPICAL 1.5 FROM TAFB. WHILE THE LOW IS NOT FAR FROM BEING MORE TROPICAL THAN SUBTROPICAL...ITS CURRENT LARGE RADIUS OF MAXIMUM WINDS...AT LEAST 120 N MI...AND ITS ENTANGLEMENT WITH AN UPPER LOW LEAD ME TO START THE SYSTEM AS A SUBTROPICAL DEPRESSION. THE INITIAL WINDS ARE SET TO 30 KT...IN AGREEMENT WITH A FEW SHIP AND BUOY OBSERVATIONS DURING THE PAST SEVERAL HOURS. MOST OF THE MODEL GUIDANCE SHOW THE UPPER-LEVEL LOW TO THE WEST-SOUTHWEST OF THE DEPRESSION MOVING SLOWLY SOUTHEASTWARD AND WEAKENING OVER THE NEXT DAY OR SO. THIS SHOULD ALLOW THE DEPRESSION TO MOVE ON THE NORTHERN SIDE OF THAT LOW...WHICH WOULD PLACE IT INTO A MORE FAVORABLE AREA FOR STRENGTHENING WITH LIGHTER WIND SHEAR. SINCE THE SYSTEM IS OVER WARM WATERS AND THE MODELS WEAKEN THE UPPER-LEVEL LOW...TRANSITION TO A TROPICAL CYCLONE SEEMS LIKELY IN A DAY OR SO. BECAUSE OF THE CURRENT STRUCTURE OF THE CYCLONE...ONLY A SLOW INTENSIFICATION IS EXPECTED BECAUSE IT COULD TAKE SOME TIME TO SHED ALL OF ITS SUBTROPICAL CHARACTERISTICS. VERTICAL WIND SHEAR IS LIKELY TO INCREASE IN A COUPLE OF DAYS... WHICH WILL PROBABLY HALT ANY STRENGTHENING AFTER THAT TIME. THE NHC INTENSITY FORECAST IS ON THE LOW SIDE OF THE GUIDANCE GIVEN THE INITIAL SUBTROPICAL STRUCTURE...AND IS GENERALLY BETWEEN THE MODEL CONSENSUS AND THE LGEM. BEST ESTIMATE OF INITIAL MOTION IS ABOUT 325/7. THE DEPRESSION IS MOVING NORTHWESTWARD BETWEEN THE UPPER-LEVEL LOW AND A LARGE RIDGE OVER THE CENTRAL ATLANTIC OCEAN. THE RIDGE SHOULD BE ERODED AWAY IN A DAY OR TWO BY A SERIES OF MID-LATITUDE TROUGHS MOVING ACROSS THE WESTERN ATLANTIC OCEAN. THIS PATTERN SHOULD CAUSE THE SYSTEM TO SLOW DOWN BY LATE TONIGHT...THEN TURN TOWARD THE NORTHEAST AND ACCELERATE BY EARLY FRIDAY DUE TO THE INCREASING MID-LATITUDE FLOW. OVERALL THE MODEL AGREEMENT IS PRETTY GOOD FOR A WEAK SYSTEM AND THE NHC FORECAST IS NEAR OR SLIGHTLY EAST OF THE DYNAMICAL MODEL CONSENSUS. EXTRATROPICAL TRANSITION SEEMS LIKELY BY 96 HR...IF NOT SOONER...AS DEPICTED BY MOST OF THE GLOBAL MODELS. FORECAST POSITIONS AND MAX WINDS INITIAL 06/0900Z 22.2N 67.0W 30 KT 12HR VT 06/1800Z 23.0N 67.7W 35 KT 24HR VT 07/0600Z 23.6N 68.0W 40 KT 36HR VT 07/1800Z 24.2N 67.5W 45 KT 48HR VT 08/0600Z 25.0N 66.1W 45 KT 72HR VT 09/0600Z 28.0N 60.5W 45 KT 96HR VT 10/0600Z 32.0N 50.0W 40 KT...POST-TROP/EXTRATROP 120HR VT 11/0600Z 36.5N 37.5W 35 KT...POST-TROP/EXTRATROP $$ FORECASTER BLAKE