MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W (EIGHTEEN) WARNING NR 01// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 18W (EIGHTEEN), LOCATED APPROXIMATELY 305 NM NORTH-NORTHEAST OF CHUUK, HAS TRACKED WEST-NORTHWESTWARD AT 18 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE (EIR) IMAGERY DEPICTS BROAD CONVECTION WITH AN ILL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC). A 281818Z SSMIS AND 281450Z AMSR2 IMAGE REVEAL FORMATIVE BROAD BANDING AROUND THE LLCC, HOWEVER, THE SYSTEM IS STILL IN ITS INFANCY AND NOT WELL CONSOLIDATED. THIS LEADS TO A LOW CONFIDENCE IN ITS INITIAL POSITION. THE INITIAL INTENSITY IS ASSESSED AT 25 KNOTS BASED ON AN AVERAGE OF THE DVORAK CURRENT INTENSITY ESTIMATES FROM ALL AGENCIES. THERE IS A FAVORABLE UPPER-LEVEL ENVIRONMENT DUE TO LOW (5 TO 10 KNOTS) OF VERTICAL WIND SHEAR (VWS) AND GOOD POLEWARD PROVIDED BY A TUTT TO THE NORTHEAST OF THE SYSTEM AND EQUATORWARD OUTFLOW. TD 18W IS TRACKING TO THE NORTHEAST ALONG THE SOUTHERN PERIPHERY OF THE DOMINANT SUBTROPICAL RIDGE (STR) TO THE NORTH. 3. FORECAST REASONING. A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST PHILOSOPHY. B. TD 18W WILL CONTINUE TO TRACK ALONG THE SOUTHWESTERN EDGE OF THE STR THROUGH THE NEXT 72 HOURS. MODELS ARE IN GOOD AGREEMENT WITH THE SYSTEM TRACKING TO THE NORTHEAST OVER THE NEXT 48 HOURS THROUGH THE NORTHERN PORTION OF THE MARIANA ISLANDS. ADDITIONALLY, EXPECT THE UPPER-LEVEL ENVIRONMENT TO IMPROVE AS A SMALL TUTT CELL TO THE NORTHWEST OF THE SYSTEM DISSIPATES, LIMITING THE VWS, AND THE NORTHEASTERN TUTT CONTINUES TO PROVIDE A GOOD POLEWARD OUTFLOW CHANNEL. ADDITIONALLY, LARGE OCEAN HEAT ENERGY CONTENT COMBINED WITH THE AFOREMENTIONED ENHANCING UPPER-LEVEL ENVIRONMENT MAY POTENTIALLY ALLOW TD 18W TO BECOME TYPHOON STRENGTH BY TAU 72. THE SPREAD IN THE MODELS BECOME MORE SIGNIFICANT NEAR TAU 72, WITH A DISPARITY OF ABOUT 250NM. C. IN THE EXTENDED FORECAST, THERE IS MODERATE DISAGREEMENT IN MODELS WITH REGARD TO THE STRENGTH OF THE STR AND WHERE TD 18W BEGINS TO TURN INTO THE BREAK IN THE RIDGE, OR EVEN IF A BREAK DEVELOPS. HWRF IS THE WESTERN, MORE FLAT OUTLIER WHILE GFDN AND COAMPS-TC (BOTH NAVGEM AND GFS) DEPICT THE EASTERN, MORE NORTHERN SCENARIO. DUE TO THE SPREAD OF OVER 450NM IN BY TAU 120, THE JTWC TRACK CLOSELY RESEMBLES THE MULTI-MODEL CONSENSUS WITH OVERALL LOW CONFIDENCE IN THE FORECAST TRACK.// NNNN NNNN