MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 20W (TWENTY) WARNING NR 02// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION 20W (TWENTY), LOCATED APPROXIMATELY 366 NM EAST-NORTHEAST OF SAIPAN, HAS TRACKED NORTHWESTWARD AT 10 KNOTS OVER THE PAST SIX HOURS. THE CURRENT POSITION IS BASED ON A 142126Z SSMIS IMAGE AND A 142322Z ASCAT PASS. THE INTENSITY OF 30 KNOTS IS CONSISTENT WITH THE ASCAT DATA AND DVORAK T-NUMBER ESTIMATES FROM MULTIPLE REPORTING AGENCIES. TD 20W CONTINUES TO TRACK NORTHWESTWARD ALONG THE PERIPHERY OF A SUBTROPICAL STEERING RIDGE TO THE NORTHEAST. THE LOW LEVEL CIRCULATION CENTER (LLCC) HAS REMAINED PARTIALLY EXPOSED DUE TO PERSISTENT EASTERLY VERTICAL WIND SHEAR. DEEP CONVECTION IS CONFINED TO THE NORTHWESTERN PERIPHERY OF THE LLCC. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS WARNING. B. TD 20W WILL CONTINUE TRACKING GENERALLY NORTHWESTWARD OVER THE NEXT 72 HOURS AS SUBTROPICAL RIDGING BECOMES FIRMLY ESTABLISHED TO THE NORTH. SLOW INTENSIFICATION IS EXPECTED IN THE NEAR-TERM AS PERSISTENT EASTERLY VERTICAL WIND SHEAR OFFSETS THE FAVORABLE INFLUENCES OF WARM SEA SURFACE TEMPERATURES AND IMPROVING WESTWARD OUTFLOW ALOFT. AFTER TAU 36, THE SYSTEM WILL LIKELY INTENSIFY MORE RAPIDLY AS VERTICAL WIND SHEAR DECREASES AND UPPER-LEVEL OUTFLOW INCREASES. DYNAMIC MODEL GUIDANCE REMAINS IN GENERALLY GOOD AGREEMENT REGARDING THE FORECAST TRACK THROUGH TAU 72. THERE IS HIGH CONFIDENCE IN THIS PORTION OF THE OFFICIAL FORECAST, WHICH LIES CLOSE TO THE MULTI-MODEL CONSENSUS. C. IN THE EXTENDED PERIOD, TD 20W WILL ROUND THE STEERING RIDGE AXIS AND ACCELERATE TOWARD THE MIDLATITUDE BAROCLINIC ZONE BY TAU 120. STEADY INTENSIFICATION IS EXPECTED AS THE SYSTEM MAKES THE TURN, BUT INCREASING VERTICAL WIND SHEAR AND PASSAGE OVER COOLER WATER WILL LIKELY WEAKEN THE SYSTEM AND INITIATE THE FIRST STAGE OF EXTRATROPICAL TRANSITION BY TAU 120. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT REGARDING TIMING OF THE AROUND TAU 72, BUT AGAIN SHOW LESS AGREEMENT REGARDING THE ORIENTATION OF THE TRACK FOLLOWING THE TURN. THE MODEL SOLUTIONS DURING THE EXTENDED PERIOD ARE FAIRLY EVENLY DISTRIBUTED AROUND THE CONSENSUS WITH NO MODEL GROUPINGS READILY APPARENT IN THE CURRENT RUN. THE OFFICIAL FORECAST LIES SLIGHTLY WEST OF THE CONSENSUS IN THE EXTENDED PERIOD, CONSISTENT WITH THE PREVIOUS FORECAST. GIVEN MODEL FORECAST SPREAD, CONFIDENCE IN THE EXTENDED TRACK FORECAST IS LOW.// NNNN NNNN