WDPN31 PGTW 032100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 31W (KALMAEGI) WARNING NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.1N 124.4E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 289 NM SOUTHEAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS WARMING
CLOUD TOPS AS TYPHOON (TY) 31W TRACKS WESTWARD OVER THE CENTRAL
PHILIPPINE ISLANDS, WEAKENING THE SYSTEM DUE TOT TOPOGRAPHIC
INTERACTION. THERE IS STRONG NORTHEASTERLY VERTICAL WIND SHEAR
(15-20KTS) RESULTING FROM ENHANCED NORTHEASTERLY UPPER-LEVEL FLOW.
AT THE SAME TIME, FLOW IS DIVERGENT, ALLOWING FOR A POLEWARD
OUTFLOW CHANNEL TO THE SOUTHWEST. THE INITIAL POSITION IS PLACED
WITH MEDIUM CONFIDENCE BASED ON THE OBSCURATION OF THE LOW-LEVEL
CIRCULATION CENTER (LLCC) IN THE AFOREMENTIONED ANIMATED EIR.
SYNOPTIC OBSERVATIONS AND PARTIAL DOPPLER RADAR LOOP ASSISTED WITH
THE POSITIONING OF THE SYSTEM. THE INITIAL INTENSITY OF 80 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 CENTERED OVER THE
LUZON STRAIT

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T5.0 - 90 KTS
   CIMSS SATCON: 75 KTS AT 031636Z
   CIMSS ADT: 77 KTS AT 031830Z
   CIMSS AIDT: 79 KTS AT 031830Z
   CIMSS D-MINT: 78 KTS AT 031726Z
   CIMSS D-PRINT: 76 KTS AT 031830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TY 31W WILL REMAIN UNDER THE STEERING
INFLUENCE OF THE WEAKENING SUBTROPICAL RIDGE TO THE NORTH FOR THE
NEXT 24 HOURS. DURING THIS TIME, TY 31W WILL COMPLETE ITS TRACK
OVER THE MAINLAND OF THE PHILIPPINES AND PASS INTO THE SOUTH CHINA
SEA. A SECONDARY RIDGE WILL BUILD OVER THE GULF OF TONKIN,
CONTINUING TO DRIVE TY 31W ALONG A WEST-NORTHWESTWARD TRACK FOR THE
REMAINDER OF THE FORECAST PERIOD. THE SYSTEM WILL MAKE LANDFALL
ALONG THE COAST OF VIETNAM IMMEDIATELY PRIOR TO TAU 72 AND WILL
REMAIN OVER LAND THROUGH TAU 96. FOR THE NEXT WE HOURS, THE SYSTEM
WILL CONTINUE TO WEAKEN TO 70KTS DUE TO TOPOGRAPHIC INTERACTION
WITH THE PHILIPPINE ISLANDS. FROM TAU 24 ON, THE SYSTEM WILL
RE-INTENSIFY GRADUALLY REACHING A PEAK OF 100KTS BY TAU 48 AS
VERTICAL WIND SHEAR DECREASES FAVORABLY (10-15KTS), UPPER-LEVEL
DIFFLUENCE REMAINS FAVORABLE, AND SEA SURFACE TEMPERATURES REMAIN
ABOVE 26C. UPON LANDFALL, THE FINAL WEAKENING TREND OF TY 31W WILL
OCCUR, INITIALLY DECREASING TO 90KTS AT TAU 72, AND CONTINUING TO
WEAKEN OVER LAND TO DISSIPATION BY THE END OF THE FORECAST PERIOD.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT TY 31W WILL REMAIN UNDER THE STEERING INFLUENCE OF THE
SUBTROPICAL RIDGE TO THE NORTH ALONG A WEST-NORTHWESTWARD TRACK.
EXCLUDING THE OUTLIER OF NAVGEM, THE CROSS-TRACK SPREAD BY LANDFALL
IS 110NM. THE INTENSITY GUIDANCE HAS A SLIGHTLY LARGER SPREAD,
DEPICTING PEAK INTENSITIES REACHING 80-115KTS BETWEEN TAU 48-60.
NOTABLY, THE OCEAN-COUPLED MODELS CAPTURE HIGHER INTENSITIES
(HWRF, HAFS-A, COAMPS-TC) WHILE THE DETERMINISTIC MODELS LIE ALONG
THE LOWER HALF OF THE RANGE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: HIGH
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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