WDPN31 PGTW 200300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 26W (TWENTYSIX) WARNING NR 001// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION 26W (TWENTYSIX), LOCATED APPROXIMATELY 433 NM SOUTHWEST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 15 KNOTS OVER THE PAST SIX HOURS. TD 26W HAS CONSOLIDATED INTO A TROPICAL CYCLONE AS THE LOW LEVEL CIRCULATION INTERACTS FAVORABLY WITH A STRONG LOW-LEVEL NORTHEASTERLY SURGE TO THE WEST. THE CURRENT POSITION IS SITUATED NEAR THE CENTER OF THE BROAD, LOW-LEVEL CIRCULATION EVIDENT IN ANIMATED MULTI-SPECTRAL SATELLITE IMAGERY, AND IS CONSISTENT WITH RECENT SUBJECTIVE POSITION FIXES FROM PGTW AND KNES. THE INTENSITY IS SET SLIGHTLY ABOVE MULTI-AGENCY SUBJECTIVE VORAK CURRENT INTENSITY ESTIMATES OF 25 KNOTS TO ACCOUNT FOR STRONGER WINDS IN THE NORTHERN AND WESTERN PORTIONS OF THE CIRCULATION, WHERE INTERACTION WITH THE NORTHEASTERLY SURGE FLOW IS OCCURRING. DEEP CONVECTION IS CURRENTLY CONFINED PRIMARILY THE WEST AND NORTHWEST OF THE CENTER, IN THE AREAS OF CONVERGENT STORM SURGE FLOW. ENVIRONMENTAL CONDITIONS ARE MARGINALLY FAVORABLE FOR DEVELOPMENT, WITH MODERATE VERTICAL WIND SHEAR (15-20 KTS), VERY WARM SEA SURFACE TEMPERATURES (28-29C), AND PRONOUNCED POLEWARD OUTFLOW ALOFT. THE SYSTEM IS TRACKING GENERALLY WESTWARD FOLLOWING THE FLOW ASSOCIATED WITH A LOW TO MID-LAYER STEERING RIDGE TO THE NORTH. 3. FORECAST REASONING. A. THIS IS THE FIRST PROGNOSTIC REASONING MESSAGE AND SETS THE FORECAST PHILOSOPHY. B. TD 26W IS EXPECTED TO FOLLOW THE FLOW ASSOCIATED WITH SUBTROPICAL RIDGING TO THE NORTH THROUGHOUT THE FORECAST PERIOD. SLOW INTENSIFICATION IS EXPECTED IN THE NEAR-TERM AS INTENSIFYING WINDS RESULTING FROM THE INTERACTION BETWEEN THE STORM AND NORTHEASTERLY SURGE WRAP INTO THE STORM CIRCULATION, AND AS MARGINALLY FAVORABLE ENVIRONMENTAL CONDITIONS SUPPORT CONVECTIVE DEVELOPMENT. PERSISTENT VERTICAL WIND SHEAR, PASSAGE OVER SLIGHTLY COOLER WATER AND SEPARATION OF THE STORM CIRCULATION FROM THE SUPPORTING SURGE FLOW SHOULD LEAD TO A WEAKENING TREND BY TAU 36, WHICH WILL CONTINUE THROUGH DISSIPATION. NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT WITH THE OVERALL TRACK FORECAST SCENARIO, WITH SMALL SPREAD THROUGH TAU 48. MODEL GUIDANCE DIVERGES AFTER THAT POINT, WHEN STORM STRUCTURE AND INTERACTION WITH ENVIRONMENTAL FLOW WILL LIKELY CHANGE RAPIDLY DUE TO WEAKENING. OVERALL, THERE IS HIGH CONFIDENCE IN THE TRACK FORECAST THROUGH TAU 48 AND FAIR CONFIDENCE BEYOND THAT POINT. C. TD 26W IS EXPECTED TO FULLY DISSIPATE BY TAU 96 AS IT CONTINUES TRACKING WESTWARD TOWARD THE MALAY PENINSULA.// NNNN