MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (THIRTY) WARNING NR 06// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 30W (THIRTY), LOCATED APPROXIMATELY 152 NM WEST-SOUTHWEST OF NAVSTA GUAM, HAS TRACKED WESTWARD AT 21 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS CLOUD BANDING THAT SUGGESTS THE LOW LEVEL CIRCULATION CENTER (LLCC) IS UNDER THE DEEPEST CONVECTION. THE INITIAL POSITION IS EXTRAPOLATED FROM INDICATIONS OF THE LLCC EVIDENT IN A 290400Z AMSR2 89 GHZ IMAGE WITH POOR CONFIDENCE. THE INITIAL INTENSITY OF 35 KNOTS IS BASED ON DVORAK CURRENT INTENSITY ESTIMATES OF T2.5 (35 KNOTS) FROM PGTW AND KNES. THE ENVIRONMENT IS FAVORABLE FOR DEVELOPMENT WITH MODERATE (10-15 KTS) VERTICAL WIND SHEAR (VWS), GOOD POLEWARD OUTFLOW, AND EXCELLENT EQUATORWARD OUTFLOW. SEA SURFACE TEMPERATURE IS ALSO FAVORABLE (28-29 CELSIUS). TS 30W IS TRACKING ALONG THE SOUTHERN PERIPHERY OF AN EAST-WEST ORIENTED SUBTROPICAL RIDGE (STR). 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 30W WILL FOLLOW A GENERALLY NORTHWESTWARD TRACK ALONG THE PERIPHERY OF THE STR THROUGHOUT THE FORECAST. PERSISTENT FAVORABLE ENVIRONMENTAL CONDITIONS WILL ALLOW FOR STEADY, FAIRLY RAPID INTENSIFICATION TO 110 KTS BY TAU 72. THE JTWC INTENSITY FORECAST FOLLOWS THE HIGH END OF THE INTENSITY GUIDANCE ENVELOPE. DYNAMIC MODEL TRACK GUIDANCE IS IN FAIR AGREEMENT WITH SPREAD BETWEEN THE MEMBERS STEADILY INCREASING TO 200 NM BY TAU 72. THE JTWC FORECAST TRACK CLOSELY FOLLOWS THE CONSENSUS WITH FAIR CONFIDENCE BASED ON THE SPREAD IN THE GUIDANCE. C. AFTER TAU 72, TS 30W WILL CONTINUE ON A NORTHWESTWARD TRACK AND INTENSIFY TO 125 KTS BY TAU 96. AFTER TAU 96, THE CYCLONE IS EXPECTED TO BEGIN WEAKENING AS THE ENVIRONMENT BECOMES LESS FAVORABLE, PRIMARILY DUE TO INCREASING VWS. FOR THIS PORTION OF THE FORECAST, SPREAD IN THE MODEL GUIDANCE INCREASES SIGNIFICANTLY, PRIMARILY DUE TO ONE MEMBER (COAMPS-GFS) WHICH DEVELOPS A BREAK IN THE STR THAT ALLOWS TS 30W TO BEGIN TRACKING POLEWARD. THE JTWC FORECAST TRACK FOLLOWS THE OTHER MEMBERS, WHICH MAINTAIN THE STR, AND KEEPS TS 30W ON A NORTHWESTWARD TO WEST-NORTHWESTWARD TRACK. SPREAD BETWEEN THE NORTHWESTWARD MEMBERS INCREASES SLIGHTLY TO 220 NM BY TAU 120, THEREFORE CONFIDENCE IN THE JTWC FORECAST TRACK IS FAIR.// NNNN NNNN