000 WTPZ42 KNHC 181708 TCDEP2 TROPICAL DEPRESSION TWELVE-E SPECIAL DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP122007 1000 AM PDT TUE SEP 18 2007 VISIBLE SATELLITE IMAGERY INDICATES THAT THE AREA OF DISTURBED WEATHER SOUTHWEST OF THE COAST OF MEXICO HAS BECOME BETTER ORGANIZED...WITH CONVECTION DEVELOPING OVER THE LOW-LEVEL CENTER. SATELLITE INTENSITY ESTIMATES ARE 25 KT FROM TAFB AND SAB...AND A QUIKSCAT OVERPASS NEAR 1330Z SUGGESTED MAXIMUM WINDS OF 25-30 KT. THE INITIAL INTENSITY IS SET TO 25 KT. THE CENTER POSITION IS A LITTLE UNCERTAIN...WITH QUIKSCAT SUGGESTING A POSITION SOMEWHAT TO THE SOUTHWEST OF MICROWAVE AND CONVENTIONAL SATELLITE IMAGERY. THIS YIELDS A SOMEWHAT UNCERTAIN MOTION OF 290/11. THE DEPRESSION IS ON THE SOUTH SIDE OF OF A MID-LEVEL RIDGE EXTENDING WESTWARD FROM NORTHERN MEXICO. THE DYNAMICAL MODELS FORECAST THIS RIDGE TO BREAK DURING THE NEXT THREE DAYS AS A LARGE DEEP-LAYER LOW MOVES SOUTHWARD OVER CALIFORNIA. THIS SHOULD ALLOW THE DEPRESSION TO TURN NORTHWARD AND THEN NORTHEASTWARD BY THE END OF THE FORECAST PERIOD. HOWEVER...THE LOW DOES NOT MOVE FAR ENOUGH SOUTH FOR ACCELERATION AFTER RECURVATURE...WITH THE GFDL AND HWRF MODELS SHOWING A SLOW EASTWARD MOTION. THE FORECAST TRACK CALLS FOR RECURVATURE AND DECELERATION DURING THE FORECAST PERIOD...WITH A LITTLE MORE NORTHERLY MOTION THAN CALLED FOR BY THE GFDL AND HWRF. THE CYCLONE IS CURRENTLY IN AN ENVIRONMENT OF LIGHT NORTHWESTERLY VERTICAL WIND SHEAR. THE LARGE-SCALE MODELS FORECAST THIS TO CONTINUE FOR 48-72 HR...FOLLOWED BY A SIGNIFICANT INCREASE IN THE SHEAR. COMBINED WITH THE DEPRESSION MOVING OVER COOLER WATER AT ABOUT 72 HR...THIS EVOLUTION WOULD SUGGEST GRADUAL STRENGTHENING THROUGH 72 HR FOLLOWED BY WEAKENING. THE INTENSITY FORECAST IS IN BEST AGREEMENT WITH THE SHIPS MODEL. THE GFDL CALLS FOR THE SYSTEM TO REACH HURRICANE STRENGTH BEFORE WEAKENING...SO THERE IS A CHANCE IT COULD BECOME STRONGER THAN FORECAST BEFORE THE SHEAR INCREASES. FORECAST POSITIONS AND MAX WINDS INITIAL 18/1700Z 13.4N 107.9W 25 KT 12HR VT 19/0000Z 13.9N 109.0W 30 KT 24HR VT 19/1200Z 14.7N 111.2W 35 KT 36HR VT 20/0000Z 15.5N 112.8W 40 KT 48HR VT 20/1200Z 16.4N 114.1W 45 KT 72HR VT 21/1200Z 18.5N 115.0W 50 KT 96HR VT 22/1200Z 20.0N 114.5W 40 KT 120HR VT 23/1200Z 21.0N 113.0W 30 KT $$ FORECASTER BEVEN