WDPN31 PGTW 031500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (YAGI) WARNING NR 
009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.8N 119.0E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 277 NM NORTH-NORTHWEST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
PARTIALLY EXPOSED LOW-LEVEL CIRCULATION SYSTEM (LLCC) DEPICTED IN A
SLOT OF DRY AIR WITH STRONG CONVECTIVE BANDING WRAPPING INTO THE
VORTEX CENTER. WATER VAPOR IMAGERY REVEALS MODERATE EASTWARD AND
STRONG EQUATORWARD UPPER-LEVEL OUTFLOW ENCOURAGING INTENSIFICATION.
A LLCC IS ALSO APPARENT ON A 031007Z 91GHZ F-17 SSMIS IMAGE WITH A
STRONG CONVECTIVE BAND NEARLY FULLY ENCIRCLING THE CENTER. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
AFOREMENTIONED ANIMATED EIR AND MICROWAVE IMAGERY. THE INITIAL
INTENSITY OF 50 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AGENCY AND OBJECTIVE FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE (STR) TO THE NORTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS ADT: 43 KTS AT 031130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 0-5 KTS
   SST: 31-32 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL STORM (TS) 12W IS FORECAST TO TRACK
IN AN OVERALL WESTWARD DIRECTION OVER THE NEXT 36 HOURS WHILE
DRIVEN BY AN ELONGATED STR TO THE NORTH. AFTER TAU 36, THE SYSTEM
WILL BEGIN TO ROUND THE SOUTHWESTERN PERIPHERY OF THE RIDGE,
STEERING TS 12W IN A WEST-NORTHWEST DIRECTION. WHILE IN THE SOUTH
CHINA SEA FOR THE NEXT 72 HOURS, THE ENVIRONMENT WILL BE FAVORABLE
WITH LOW VERTICAL WIND SHEAR (5-10KTS), STRONG UPPER-LEVEL
DIVERGENCE, AND WARM SEA SURFACE TEMPERATURES (31-32C). HOWEVER,
WHAT WILL PUSH TS 12W OVER THE EDGE TO RAPIDLY INTENSIFY IS HIGH
OCEAN HEAT CONTENT WHICH WILL FUEL THE SYSTEM TO QUICKLY PEAK TO
110KTS AT TAU 60. (NOT REFLECTED IN THE WARNING DUE TO TEMPORAL
RESOLUTION BETWEEN TAU 48-72.) AFTER TAU 72, THE SYSTEM WILL BEGIN
TO ENTER A REGION OF MODERATE SHEAR (10-15KTS) AND BEGIN TO
INTERACT WITH THE TOPOGRAPHY OF HAINAN ISLAND AND LUICHOW
PENINSULA. AFTER EMERGING OVER THE GULF OF TONKIN, TS 12W WILL
BEGIN DISSIPATING AT TAU 96 AFTER MAKING LANDFALL ON MAINLAND
VIETNAM AND REACH FULL DISSIPATION OVER LAND BY TAU 120.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
WITHIN THE FIRST 48 HOURS OF THE FORECAST, BUT SPREADS AFTER TAU 36
BASED ON VARIED MODEL SOLUTIONS OF THE ANGLE WHICH TS 12W WILL
BEGIN TO ROUND THE STR TO THE NORTH. THE CROSS-TRACK SPREAD IS
218NM BY TAU 120, LEAVING THE LATE-TERM FORECAST WITH MEDIUM
CONFIDENCE. THE JTWC INTENSITY GUIDANCE ALSO IS IN GOOD AGREEMENT
THAT A PEAK WILL OCCUR AT TAU 60, WITH A SPREAD OF 35KTS. THE
LOWEST INTENSITY OF 90KTS IS REPRESENTED BY THE JTWC SHIPS GUIDANCE
WHILE THE HIGHEST PEAK INTENSITY IS REPRESENTED BY COAMPS-TC. RAPID
INTENSIFICATION AIDS FRIA, RICN, AND RIPA ALL WERE TRIGGERED BY
THE FAVORABLE ENVIRONMENT PREVIOUSLY MENTIONED IN THE FORECAST
DISCUSSION. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
NNNN