MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 31W (THIRTYONE) WARNING NR 01// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 31W (THIRTYONE), LOCATED APPROXIMATELY 812 NM EAST-SOUTHEAST OF ANDERSEN AFB, GUAM, HAS TRACKED WESTWARD AT 12 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS AN AREA OF DEEP AND SPIRALING CONVECTION WHICH CONTINUES TO CONSOLIDATE. THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE AND IS BASED ON A 211200Z HIMAWARI INFRARED SATELLITE IMAGE. THE INITIAL INTENSITY OF 25 KNOTS IS BASED ON DVORAK INTENSITY ESTIMATES OF T1.5 (25 KNOTS) FROM PGTW, KNES AND RJTD ALONG WITH A PARTIAL 211041Z METOP-B ASCAT IMAGE SHOWING 25 KNOT WINDS. ENVIRONMENTAL ANALYSIS SHOWS THAT TD 31W IS EXPERIENCING FAVORABLE VERTICAL WIND SHEAR (5 TO 10 KNOTS) ALONG WITH IMPROVING RADIAL OUTFLOW. SEA SURFACE TEMPERATURES ARE ALSO FAVORABLE FOR DEVELOPMENT, BETWEEN 30 AND 32 DEGREES CELSIUS. TD 31W IS TRACKING WESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) LOCATED TO THE NORTHEAST. 3. FORECAST REASONING. A. THIS IS THE INITIAL PROGNOSTIC REASONING MESSAGE FOR THIS SYSTEM AND SETS THE FORECAST PHILOSOPHY. B. THROUGH TAU 72, TD 31W WILL TRACK TO THE NORTHWEST ALONG THE SOUTHWESTERN EDGE OF THE AFOREMENTIONED STR. ENVIRONMENTAL CONDITIONS (VERTICAL WIND SHEAR, UPPER LEVEL OUTFLOW, AND SEA SURFACE TEMPERATURES) WILL ALL REMAIN FAVORABLE AND ALLOW FOR TD 31W TO STEADILY INCREASE IN INTENSITY. BY TAU 72, TD 31W WILL REACH AN INTENSITY OF 110 KNOTS. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT THAT TD 31W WILL TRACK NORTHWESTWARD THROUGH TAU 72. HOWEVER, MODEL GUIDANCE CONTINUES TO DIVERGE FROM THE INITIAL POSITION WITH A SPREAD OF 270 NM BY TAU 72. THEREFORE, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK. C. BEYOND TAU 72, TD 31W WILL BEGIN TO TURN NORTHWARD DUE TO A WEAKNESS IN THE STR. TD 31W WILL STILL EXPERIENCE FAVORABLE ENVIRONMENTAL CONDITIONS AND WILL REACH A PEAK INTENSITY OF 125 KNOTS BY TAU 96 AND MAINTAIN THAT INTENSITY THROUGH TAU 120. THE PEAK INTENSITY WILL OCCUR AS TD 31W ROUNDS THE WESTERN EDGE OF THE STR TO THE EAST AND BEGINS TO TAP INTO ENHANCED POLEWARD OUTFLOW AND TRAVEL OVER WATER WITH HIGH OCEAN HEAT CONTENT. DYNAMIC MODEL GUIDANCE IS IN POOR AGREEMENT WITH AFUM INDICATING A NORTHWESTWARD TRACK WHILE GFS IS INDICATING A RECURVE SCENARIO WITH A DIFFERENCE BETWEEN THOSE MODELS OF 720 NM BY TAU 120. THE JTWC FORECAST TRACK IS PLACED NEAR THE MULTIMODEL CONSENSUS. DUE TO THE DIFFERENCES IN MODEL GUIDANCE THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK.// NNNN NNNN