000 WTPZ41 KNHC 162040 TCDEP1 TROPICAL STORM MARTY DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP162009 200 PM PDT WED SEP 16 2009 VISIBLE SATELLITE IMAGERY INDICATES THAT MARTY HAS MOVED VERY LITTLE SINCE THIS MORNING. THE CLOUD PATTERN IS THAT OF A VERY ASYMMETRIC TROPICAL CYCLONE...WITH ALL OF THE DEEP CONVECTION OVER THE WESTERN SEMICIRCLE OF THE STORM. DVORAK T-NUMBERS OF 2.5 AND 3.0 SUPPORT INCREASING THE INITIAL INTENSITY TO 40 KT. A SHEAR ANALYSIS FROM UW-CIMSS SHOWS ABOUT 15 KT OF SOUTHEASTERLY SHEAR OVER THE CYCLONE. THE SHEAR IS FORECAST TO BECOME SOUTHERLY...THEN TURN SOUTHWESTERLY IN ABOUT 24 HOURS. IT APPEARS THAT THERE IS SMALL WINDOW OF OPPORTUNITY FOR MARTY TO STRENGTHEN DURING THE NEXT DAY... THEREAFTER INCREASING SHEAR AND A LESS FAVORABLE THERMODYNAMIC ENVIRONMENT SHOULD INDUCE A MORE RAPID RATE OF WEAKENING. THE OFFICIAL INTENSITY FORECAST IS CLOSEST TO THE STATISTICAL GUIDANCE FOR THE FIRST 24 HOURS...THEN IS IN GOOD AGREEMENT WITH THE INTENSITY CONSENSUS THEREAFTER. MARTY IS EXPECTED TO BEGIN MOVING SLOWLY NORTH-NORTHWESTWARD SOON AS A WEAK RIDGE BUILDS TO THE EAST OF THE CYCLONE. THE NEW FORECAST IS CLOSE TO THE PREVIOUS ADVISORY AND NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE DURING THE FIRST 48 HOURS. THEREAFTER...A SIGNIFICANT WESTWARD SHIFT HAS BEEN MADE TO THE NHC TRACK...AS NEARLY ALL OF THE DYNAMICAL MODELS TURN MARTY WESTWARD IN THE LOW-LEVEL FLOW AS IT WEAKENS AND BECOME A SHALLOW SYSTEM. FORECAST POSITIONS AND MAX WINDS INITIAL 16/2100Z 18.9N 112.6W 40 KT 12HR VT 17/0600Z 19.2N 112.7W 45 KT 24HR VT 17/1800Z 19.7N 113.0W 50 KT 36HR VT 18/0600Z 20.4N 113.4W 45 KT 48HR VT 18/1800Z 21.2N 113.9W 35 KT 72HR VT 19/1800Z 22.6N 115.3W 30 KT...REMNANT LOW 96HR VT 20/1800Z 23.5N 117.0W 25 KT...REMNANT LOW 120HR VT 21/1800Z 23.5N 120.0W 20 KT...REMNANT LOW $$ FORECASTER BROWN