000 WTPZ41 KNHC 231452 TCDEP1 TROPICAL STORM HILDA DISCUSSION NUMBER 5 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP112009 800 AM PDT SUN AUG 23 2009 INFRARED AND MICROWAVE SATELLITE IMAGERY INDICATES THAT THE CENTER OF HILDA HAS REMAINED PARTIALLY EXPOSED ON THE NORTHEAST SIDE OF A PULSATING MASS OF DEEP CONVECTION MOST OF THE NIGHT. MORE RECENTLY...HOWEVER...A NEW BURST OF CONVECTION HAS OVERSPREAD THE CIRCULATION CENTER. EVEN THOUGH DVORAK T-NUMBERS HAVE INCREASED TO 3.0 AT 1200 UTC...THERE HAS BEEN A GENERAL LACK OF IMPROVEMENT IN ORGANIZATION. FOR THIS REASON...THE INITIAL INTENSITY IS BEING HELD AT 40 KT. MODERATE NORTHEASTERLY SHEAR HAS PERSISTED OVER THE CYCLONE AND GLOBAL MODELS FORECAST THIS SHEAR TO CONTINUE FOR THE NEXT 3 DAYS. IT APPEARS THAT THE SHEAR SHOULD BE ENOUGH TO INHIBIT SIGNIFICANT INTENSIFICATION DURING THIS TIME...DESPITE SUFFICIENTLY WARM WATERS. BEYOND 72 HOURS...MODEL GUIDANCE BREAKS OFF A PIECE OF A DEEP UPPER-LEVEL TROUGH ALONG 135W AND DIGS ITS SOUTHWARD EAST OF THE HAWAIIAN ISLANDS. THIS FEATURE SHOULD BEGIN TO PRODUCE A WESTERLY OR NORTHWESTERLY SHEAR OVER HILDA LATE IN THE PERIOD...WHICH WOULD LIMIT INTENSIFICATION. SIMILAR TO THE PREVIOUS ADVISORY...THE OFFICIAL FORECAST CONTINUES TO CALL FOR ONLY SLOW STRENGTHENING...IN LINE WITH THE INTENSITY CONSENSUS MODEL. RECENT SATELLITE FIXES ARE A BIT UNCERTAIN BUT YIELD AN INITIAL MOTION ESTIMATE OF 275/08. A WEAK BUT DEEP-LAYER EASTERLY FLOW SOUTH OF A MID-LEVEL RIDGE HAS BEEN GUIDING HILDA ON AN ALMOST DUE-WEST COURSE. LARGE-SCALE MODELS FORECAST A MID- TO UPPER-LEVEL CYCLONIC FEATURE NEAR 23N148W TO GRADUALLY LIFT NORTHEAST THE NEXT FEW DAYS...KEEPING THE RIDGE TO THE NORTH OF HILDA WEAK OVER THE NEXT SEVERAL DAYS. AS A RESULT...HILDA SHOULD CONTINUE ON A SLOW BUT GENERAL WESTERLY COURSE. THEREAFTER...THE SPREAD IN THE GUIDANCE INCREASES AS SEVERAL MODELS KEEP A WEAK STEERING REGIME OVER HILDA...WHILE THE GFDL/HWRF BUILD A STRONGER RIDGE TO THE NORTHWEST AND MOVE HILDA FASTER TOWARD THE WEST OR WEST-SOUTHWEST. THE OFFICIAL FORECAST LIES BETWEEN THE TWO EXTREMES AND IS CLOSE TO THE PREVIOUS TRACK AND THE DYNAMICAL MODEL CONSENSUS. FUTURE ADVISORIES ON HILDA WILL BE ISSUED BY THE CENTRAL PACIFIC HURRICANE CENTER UNDER AWIPS HEADER TCDCP5 AND WMO HEADER WTPA45 PHFO. FORECAST POSITIONS AND MAX WINDS INITIAL 23/1500Z 13.8N 140.1W 40 KT 12HR VT 24/0000Z 13.9N 141.4W 40 KT 24HR VT 24/1200Z 14.2N 143.1W 45 KT 36HR VT 25/0000Z 14.5N 144.8W 45 KT 48HR VT 25/1200Z 14.8N 146.5W 50 KT 72HR VT 26/1200Z 14.8N 149.7W 50 KT 96HR VT 27/1200Z 15.0N 152.5W 55 KT 120HR VT 28/1200Z 15.0N 155.5W 55 KT $$ FORECASTER KIMBERLAIN/PASCH