WDPN32 PGTW 170300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 26W (NOUL) WARNING NR 05//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TS 26W (NOUL) HAS SLOWLY INTENSIFIED WHILE CONTINUING GENER-
ALLY WESTWARD OVER THE PAST 12 HOURS. DEEP CONVECTION HAS INCREASED
OVER THE WESTERN SEMICIRCLE OF THE CIRCULATION IN REPSONSE TO STRONG
UPPER LEVEL DIFFLUENCE AND PASSAGE ACROSS A HIGH HEAT CONTENT SEA
SURFACE.
   B. THE CURRENT POSITION IS BASED ON RECENT SATELLITE FIXES FROM
PGTW AND RJTD AND A PARTIAL 162343Z SSMIS PASS. THE INTENSITY ESTI-
MATE OF 40 KNOTS IS CONSISTENT WITH DVORAK T-NUMBERS OF 3.0 FROM
PGTW AND 2.5 FROM RJTD AND LOW LEVEL STRUCTURE NOTED IN MICROWAVE
SATELLITE IMAGERY. TS 26W IS TRACKING WESTWARD ALONG THE SOUTHERN
PERIPHERY OF A ZONALLY-ORIENTED STEERING RIDGE TO THE NORTH. TS 26W
LIES POLEWARD OF AN UPPER LEVEL RIDGE AXIS, IN A REGION OF MODERATE
VERTICAL WIND SHEAR AND FAVORABLE WESTWARD AND POLEWARD OUTFLOW.
3. FORECAST REASONING
   A. THE TRACK FORECAST HAS BEEN SHIFTED SLIGHTLY POLEWARD IN THE
NEAR TERM BASED ON RECENT STORM MOTION, INCREASING THE ANTICIPATED
OVER-LAND TRACK IN THE TAU 12 TO TAU 36 PERIOD. MEDIUM TERM
INTENSITIES HAVE BEEN NUDGED LOWER IN RESPONSE TO THIS TRACK SHIFT.
DESPITE THESE UPDATES, THE OVERALL FORECAST PHILOSOPHY HAS NOT
CHANGED SINCE THE PREVIOUS ISSUANCE OF THE PROGNOSTIC REASONING
MESSAGE.
   B. TS 26W WILL CONTINUE TRACKING GENERALLY WESTWARD ALONG THE
SOUTHERN PERIPHERY OF THE CURRENT STEERING RIDGE THROUGH TAU 72.
THE TROPICAL STORM WILL MAKE LANDFALL IN SOUTHERN VIETNAM AROUND
TAU 12 AND CONTINUE OVER LAND UNTIL REEMERGING OVER THE GULF OF
THAILAND JUST PRIOR TO TAU 36. ALTHOUGH THE SYSTEM IS EXPECTED TO
ENCOUNTER ELEVATED TERRAIN UPON LANDFALL, THE CIRCULATION WILL
SPEND MOST OF THE TAU 12 TO TAU 36 PERIOD OVER MUCH FLATTER
TERRAIN, WHICH SHOULD ALLOW TS 26W TO REMAIN AT OR ABOVE THE
WARNING INTENSITY THRESHOLD OF 25 KNOTS UNTIL THE CYCLONE MOVES
OVER WATER ONCE AGAIN. HOWEVER, THE POTENTIAL EXISTS FOR FULL
DISSIPATION OF THE SYSTEM AS IT CONTINUES OVER LAND, DEPENDING ON
THE EXACT TRACK AND THE EFFECT OF THE TERRAIN ON STORM ORGANIZATION.
ASSUMING THE CYCLONE REMAINS INTACT, IT WILL MOVE GENERALLY
WESTWARD UNDER THE CONTINUED STEERING INFLUENCE OF RIDGING TO
THE NORTH AFTER TAU 36. GOOD UPPER LEVEL DIFFLUENCE AND PASSAGE
ACROSS A VERY WARM SEA SURFACE WILL INDUCE SLOW INTENSIFICATION
BETWEEN TAU 36 AND TAU 72. THE CURRENT TRACK FORECAST IS CLOSE
TO THE NUMERICAL GUIDANCE, WHICH REFLECTS GOOD AGREEMENT AMONG
FORECAST MODELS.
   C. IN THE EXTENDED PERIOD, TS 26W WILL CONTINUE PROGRESSING
WESTWARD TO WEST-NORTHWESTWARD ACROSS THE BAY OF BENGAL, PROVIDED
THAT THE CIRCULATION SURVIVES A PERIOD OF LAND INTERACTION IN
THE EARLIER TAUS AND SUSTAINED LOW TO MODERATE EASTERLY VERTICAL
WIND SHEAR.
FORECAST TEAM: ALPHA//