MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (TWENTYEIGHT) WARNING NR 01// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 28W (TWENTYEIGHT), LOCATED APPROXIMATELY 13 NM EAST-NORTHEAST OF ANDERSEN AFB, HAS TRACKED NORTHWESTWARD AT 08 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS FLARING DEEP CONVECTION NEAR THE LOW LEVEL CIRCULATION CENTER (LLCC) AND BANDING FEATURES STARTING TO DEVELOP, ESPECIALLY TO THE SOUTHEAST OF THE LLCC. THE INITIAL POSITION IS PLACED WITH GOOD CONFIDENCE BASED ON RADAR IMAGERY FROM GUAM AND IS SUPPORTED BY OBSERVATIONS FROM THE SURROUNDING ISLANDS. THE INITIAL INTENSITY IS BASED ON THE PGTW AND KNES DVORAK CURRENT INTENSITY ESTIMATES OF T1.5 (25 KNOTS). ENVIRONMENTAL CONDITIONS FOR TD 28W ARE GENERALLY FAVORABLE WITH GOOD EQUATORWARD AND POLEWARD OUTFLOW, LOW TO MODERATE VERTICAL WIND SHEAR, AND WARM SSTS (28-29 CELSIUS). TD 28W IS CURRENTLY TRACKING ALONG A SOUTHERN EXTENSION OF AN OTHERWISE EAST-WEST ORIENTED SUBTROPICAL RIDGE (STR) TO THE NORTH. 3. FORECAST REASONING. A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST PHILOSOPHY. B. BY TAU 24, TD 28W IS FORECAST TO GRADUALLY TURN ONTO A WESTWARD TRACK AS THE EAST-WEST ORIENTATION OF THE STR BECOMES THE DOMINANT INFLUENCE ON THE TRACK. THE STR TO THE NORTH WILL MAINTAIN A GENERALLY WESTWARD TRACK THROUGH TAU 72. DURING THIS PERIOD, THE ENVIRONMENT REMAINS FAVORABLE AND TD 28W IS EXPECTED TO RAPIDLY INTENSIFY TO 115 KTS BY TAU 72. THE INTENSITY FORECAST CLOSELY FOLLOWS THE INTENSITY CONSENSUS, HOWEVER SPREAD IS QUITE LARGE AMONG THE MEMBERS WITH CTCI (130 KTS) AND COTI (75 KTS) REPRESENTING THE EXTREMES AT TAU 72. MODEL TRACK GUIDANCE HAS ABOUT 170 NM OF SPREAD BY TAU 72, THEREFORE CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST IS FAIR. C. AFTER TAU 72, AN APPROACHING MID-LATITUDE TROUGH IS EXPECTED TO CREATE A WEAKNESS IN THE STR AND ALLOW TD 28W TO BEGIN ROTATING POLEWARD AROUND THE RIDGE AXIS. THE INTENSITY IS EXPECTED TO CONTINUE TO GRADUALLY INCREASE AS CONDITIONS REMAIN FAVORABLE. HOWEVER, BY TAU 120 THE JTWC FORECAST INTENSITY IS PLACED ABOVE THE INTENSITY GUIDANCE BASED ON THE EXPECTATION THAT THE MID-LATITUDE TROUGH WILL BE JUST WEST OF THE TROPICAL CYCLONE AND AID POLEWARD OUTFLOW. HOWEVER, IF THE TROUGH PASSES TO THE EAST SOONER, THE CYCLONE WILL BEGIN TO WEAKEN. DURING THIS PERIOD, MODEL TRACK GUIDANCE BECOMES MORE UNCERTAIN DUE TO DIFFERENCES IN THE TIMING AND DEGREE OF RE-CURVATURE AROUND THE STR AXIS. FOR THIS REASON, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK.// NNNN NNNN