000 WTPZ41 KNHC 230837 TCDEP1 TROPICAL STORM HILDA DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP112009 200 AM PDT SUN AUG 23 2009 ALTHOUGH THE CIRCULATION CENTER OF HILDA REMAINS PARTIALLY EXPOSED THIS EVENING...SPIRAL BANDING OVER THE WESTERN PORTION OF THE CYCLONE HAS BECOME BETTER ORGANIZED. FURTHERMORE...ENHANCED INFRARED IMAGERY INDICATES VERY COLD CLOUD TOP TEMPERATURES ASSOCIATED WITH THE BANDING FEATURE AND A FEW RECENT BURSTS OF DEEP CONVECTION NEAR THE CENTER. BASED ON THE IMPROVED CLOUD PATTERN AND A COMPROMISE OF THE DVORAK INTENSITY ESTIMATES...THE INITIAL INTENSITY IS RAISED TO 40 KT. THE OCEANIC ENVIRONMENT IS EXPECTED TO BE REMAIN FAVORABLE DURING THE FORECAST PERIOD...BUT THE UPPER WIND PATTERN WILL BE ONLY MARGINALLY CONDUCIVE FOR STRENGTHENING DUE TO PERSISTENT NORTHEASTERLY SHEAR. CONSEQUENTLY...THE INTENSITY FORECAST CALLS FOR GRADUAL INTENSIFICATION DURING THE NEXT 5 DAYS...SIMILAR TO THE ICON INTENSITY CONSENSUS MODEL. INITIAL MOTION IS ESTIMATED AT 275/8...WITHIN THE DEEP-LAYER EASTERLY FLOW OF A HIGH PRESSURE TO THE NORTH. A MID- TO UPPER LEVEL TROUGH LOCATED A FEW HUNDRED MILES EAST-NORTHEAST OF THE HAWAIIAN ISLANDS SHOULD CAUSE THE CYCLONE TO SLOW A BIT AND TURN MORE TOWARD THE WEST-NORTHWEST...AS INDICATED BY THE GFDL/GFS AND ECMWF...AROUND MID-PERIOD. AFTERWARD...RIDGING IS FORECAST TO BUILD NORTHWEST OF HILDA IN RESPONSE TO THE AFOREMENTIONED TROUGH FILLING AND MOVING NORTHEASTWARD OUT OF THE AREA. THIS CHANGE IN THE STEERING PATTERN NEAR DAY 3 IS EXPECTED TO TURN THE CYCLONE BACK TOWARD THE WEST. THE OFFICIAL FORECAST IS CLOSE TO THE PREVIOUS TRACK AND COINCIDES WITH THE DYNAMICAL MODEL CONSENSUS. FORECAST POSITIONS AND MAX WINDS INITIAL 23/0900Z 13.7N 139.3W 40 KT 12HR VT 23/1800Z 13.9N 140.6W 40 KT 24HR VT 24/0600Z 14.3N 142.2W 45 KT 36HR VT 24/1800Z 14.6N 144.0W 45 KT 48HR VT 25/0600Z 14.8N 145.7W 50 KT 72HR VT 26/0600Z 15.0N 149.0W 50 KT 96HR VT 27/0600Z 15.0N 152.0W 55 KT 120HR VT 28/0600Z 15.0N 155.0W 55 KT $$ FORECASTER ROBERTS/BROWN