WDPN31 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 31W (KALMAEGI) WARNING NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.9N 119.9E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 231 NM SOUTH-SOUTHWEST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
(TY) 31W STRENGTHENING AS CLOUD TOPS COOL SIGNIFICANTLY, PRODUCING
SOME OVERSHOOTING TOPS, AND THE CONVECTIVE STRUCTURE BECOMES MORE
SYMMETRIC. VERTICAL WIND SHEAR HAS DECREASED SIGNIFICANTLY ALLOWING
FOR RE-INTENSIFICATION TO BEGIN AS THE SYSTEM PASSES INTO THE SOUTH
CHINA SEA. WATER VAPOR IMAGERY REVEALS STRONG DIFFLUENT
NORTHEASTERLY FLOW ALLOWING FOR AN EQUATORWARD EXHAUST CHANNEL. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
AFOREMENTIONED EIR, LOCAL OBSERVATIONS, AND A 04 NOAA-21 ATMS 89GHZ
MICROWAVE IMAGER REVEALING AN UPPER-LEVEL MICROWAVE EYE FEATURE.
THE INITIAL INTENSITY OF 70 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 TO THE NORTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T4.5 - 77 KTS
   KNES: T4.5 - 77 KTS
   DEMS: T4.5 - 77 KTS
   CIMSS SATCON: 63 KTS AT 041758Z
   CIMSS ADT: 63 KTS AT 041730Z
   CIMSS AIDT: 56 KTS AT 041730Z
   CIMSS D-MINT: 61 KTS AT 041708Z
   CIMSS D-PRINT: 55 KTS AT 041900Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 ON A WEST-NORTHWESTWARD
TRACK FOR THE REMAINDER OF THE FORECAST PERIOD AS THE SYSTEM
REMAINS STEERED BY THE SUBTROPICAL RIDGE CENTERED OVER THE GULF OF
TONKIN. TY 31W WILL MAKE LANDFALL ON THE CENTRAL COAST OF VIETNAM
IMMEDIATELY FOLLOWING TO TAU 72. THE SYSTEM WILL CONTINUE TO
INTENSIFY THROUGH TAU 36 IN A MARGINALLY FAVORABLE ENVIRONMENT OF
WARM SEA SURFACE TEMPERATURES AND DIFFLUENT OUTFLOW EQUATORWARD,
HOWEVER, VERTICAL WIND SHEAR WILL REMAIN MARGINALLY HIGH
APPROXIMATELY 20KTS THROUGHOUT THE FORECAST PERIOD. WEAKENING WILL
OCCUR DUE TO LANDFALL, ULTIMATELY CAUSING TY 31W TO DISSIPATE BY
TAU 72. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN STRONG
AGREEMENT WITH A CROSS-TRACK SPREAD OF 75NM BY LANDFALL. THE LOW
CROSS-TRACK SPREAD CONTRIBUTES TO HIGH CONFIDENCE IN THE FORECAST.
THE INTENSITY GUIDANCE IS SLIGHTLY BROADER WITH PEAKS SPREAD
BETWEEN 80KTS (COAMPS-TC) TO 100KTS (HAFS-A). THE JTWC FORECAST
LIES CLOSELY TO THE MEAN, CONTRIBUTING TO HIGH CONFIDENCE IN THE
INTENSITY FORECAST.

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