WDPN31 PGTW 121500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (KALMAEGI) WARNING 
NR 08//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 15W (KALMAEGI), LOCATED APPROXIMATELY 508 NM 
EAST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 11 KNOTS OVER 
THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE 
IMAGERY DEPICTS INCREASED DEEP CENTRAL CONVECTION WITH FORMATIVE 
CONVECTIVE BANDING OBSCURING A CONSOLIDATING LOW-LEVEL CIRCULATION 
CENTER (LLCC). A 121223Z METOP-B MICROWAVE IMAGE REVEALS TIGHTLY-
CURVED CONVECTIVE BANDING OVER THE NORTHERN AND SOUTHERN PERIPHERY 
WRAPPING INTO THE LLCC. THE CURRENT POSITION IS BASED ON THE EIR 
ANIMATION AND AFOREMENTIONED MICROWAVE IMAGE WITH FAIR CONFIDENCE. 
THE INITIAL INTENSITY OF 40 KNOTS IS BASED ON AN OVERALL ASSESSMENT 
OF A 121223Z ASCAT PASS AND DVORAK INTENSITY ESTIMATES FROM ALL 
REPORTING AGENCIES. UPPER-LEVEL ANALYSIS INDICATES THE SYSTEM IS 
LOCATED IN AN AREA OF LOW TO MODERATE (10 TO 20 KNOT) EASTERLY 
VERTICAL WIND SHEAR OFFSET BY EXCELLENT EQUATORWARD OUTFLOW AND THE 
STORM MOTION. TS 15W CONTINUES TRACKING WESTWARD UNDER THE STEERING 
INFLUENCE OF THE DEEP LAYERED REFLECTION OF THE SUBTROPICAL RIDGE 
(STR) LOCATED TO THE NORTH OF THE SYSTEM.
3. FORECAST REASONING.
   A. THE SHORT-TERM INTENSITY FORECAST HAS BEEN INCREASED DUE TO 
INCREASED DEEP CONVECTION AND CONSOLIDATION. 
   B. TS 15W IS FORECAST TO TRACK WESTWARD TO WEST-NORTHWESTWARD 
UNDER THE STEERING INFLUENCE OF THE STR, BUT IS EXPECTED TO UNDERGO 
A PERIOD OF DECREASED SPEEDS AS A MIGRATORY UPPER-LEVEL TROUGH 
PASSES TO THE NORTH OF THE RIDGE OVER THE NEXT 36 HOURS. IN ADDITION 
TO CONDUCIVE SEA SURFACE TEMPERATURES, FAVORABLE ENVIRONMENTAL 
CONDITIONS AND IMPROVED UPPER-LEVEL CONDITIONS ARE EXPECTED TO 
PERSIST ALLOWING TS 15W TO INTENSIFY, REACHING TYPHOON STRENGTH BY 
TAU 24. TS KALMAEGI IS FORECAST TO MAKE LANDFALL INTO EASTERN LUZON 
AROUND TAU 48, LEADING TO A TEMPORARY WEAKENING AS IT DRIFTS ACROSS 
THE TERRAIN.
   C. IN THE EXTENDED TAUS, TS 15W IS EXPECTED TO MAINTAIN A WEST- 
NORTHWESTWARD TRACK THROUGH THE REMAINDER OF THE FORECAST PERIOD AS 
THE STR REBUILDS TO THE NORTH. FAVORABLE ENVIRONMENTAL CONDITIONS IN 
THE SOUTH CHINA SEA (SCS) WILL FURTHER ALLOW TS 15W TO INTENSIFY AS 
IT TRACKS ACROSS THE NORTHERN SCS. AFTER TAU 96, TS KALMAEGI IS 
FORECAST TO WEAKEN AS IT APPROACHES THE SOUTHERN COAST OF CHINA.
AVAILABLE MODEL GUIDANCE REMAINS IN GOOD AGREEMENT; HOWEVER, DUE TO 
THE UNCERTAINTY OF INTENSITY AND TRACK SPEEDS IN THE EXTENDED TAUS, 
THERE IS LOW CONFIDENCE IN THE JTWC FORECAST, WHICH IS POSITIONED 
CLOSE TO MULTI-MODEL CONSENSUS.//
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