WDPN31 PGTW 012100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 31W (KALMAEGI) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.6N 136.4E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 120 NM WEST-NORTHWEST OF YAP
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM (TS) 31W WITH AN EXPANDING CENTRAL DENSE OVERCAST (CDO) AND
DEVELOPING CIRRUS FILAMENTS WITHIN THE OUTFLOW CHANNELS. THE
ENVIRONMENT IS HIGHLY FAVORABLE FOR CONTINUED INTENSIFICATION, WITH
LOW (0-5 KTS) VERTICAL WIND SHEAR, VERY WARM (29-30 C) SEA SURFACE
TEMPERATURES, AND STRONG DIVERGENCE ALOFT BOLSTERING DEVELOPMENT.
THE EQUATORWARD AND WESTWARD OUTFLOW CHANNELS ARE ENHANCED BY
INTERACTION WITH THE EQUATORIAL TRADE WINDS TO THE SOUTH. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A 011627Z
AMSR2 37GHZ COLOR ENHANCED MICROWAVE IMAGE REVEALING THE LOW-LEVEL
CLOUD BANDS WRAPPING INTO THE CENTER. THE INITIAL INTENSITY OF 40
KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE CIMSS OBJECTIVE
INTENSITY ESTIMATES AND AGENCY DVORAK FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: THE SOUTHWESTERN EXTENSION OF THE
SUBTROPICAL RIDGE CENTERED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   CIMSS SATCON: 39 KTS AT 011623Z
   CIMSS ADT: 35 KTS AT 011730Z
   CIMSS AIDT: 32 KTS AT 011730Z
   CIMSS D-MINT: 34 KTS AT 011623Z
   CIMSS D-PRINT: 46 KTS AT 011730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 31W (KALMAEGI) IS FORECAST TO CONTINUE
NORTHWESTWARD UNTIL TAU 12, AS THE STORM REMAINS UNDER THE STEERING
INFLUENCE OF SOUTHWESTERN EXTENSION OF THE STR TO ITS NORTHEAST.
BEGINNING AROUND TAU 12, A STR OVER THE SOUTH CHINA SEA WILL BUILD,
CAUSING 31W TO TRANSITION STEERING RIDGES AND TRACK WESTWARD UNTIL
LANDFALL IN THE PHILIPPINES. LANDFALL IS EXPECTED TO OCCUR ON SAMAR
ISLAND JUST AFTER TAU 48, WITH REEMERGENCE IN THE SOUTH CHINA SEA
BEFORE TAU 72. AFTER TAU 72 THROUGH THE REMAINDER OF THE FORECAST
PERIOD, KALMAEGI WILL TRACK NORTHWESTWARD, ROUNDING THE
SOUTHEASTERN PERIPHERY OF THE STR, WHICH WILL SHIFT SLIGHTLY
NORTHWARD OVER TAIWAN. REGARDING INTENSITY, 31W IS IN A PRIME
ENVIRONMENT FOR RAPID INTENSIFICATION. VERTICAL WIND SHEAR IS
EXPECTED TO REMAIN LOW THROUGH TAU 48, WHILE THE FORECAST TRACK
LIES IN A REGION OF HIGH OCEAN HEAT CONTENT TO THE EAST OF THE
PHILIPPINES. THOSE FACTORS, COMBINED WITH ROBUST DIVERGENCE ALOFT,
CONTRIBUTE TO KALMAEGI'S ANTICIPATED RAPID INTENSIFICATION TO AT LEAST 
90 KTS AT TAU 48. 31W WILL WEAKEN SLIGHTLY BETWEEN TAU 48-72 AS IT
TRAVERSES THE CENTRAL PHILIPPINES BUT IS FORECAST TO REEMERGE OVER
WATER AT TYPHOON STRENGTH. 31W WILL ENTER A SECOND INTENSIFICATION
PHASE AS IT WILL CONTINUE TO BE FUELED BY THE HIGHLY FAVORABLE
ENVIRONMENT IN THE SOUTH CHINA SEA, RESULTING IN INTENSIFICATION
FROM 80 KTS AT TAU 72 TO ITS PEAK OF 105 KTS AT TAU 120. 

MODEL DISCUSSION: DETERMINISTIC TRACK MODEL GUIDANCE IS IN STRONG
AGREEMENT THROUGH TAU 48, WITH NAVGEM BEING THE ONLY OUTLIER. ONCE
31W MAKES LANDFALL, HOWEVER, MODEL GUIDANCE DIVERGES SLIGHTLY IN BOTH
THE ALONG-TRACK AND CROSS-TRACK DIRECTIONS AS THE STORM TRANSITS
THE PHILIPPINE ARCHIPELAGO. DISCOUNTING NAVGEM, THE SLIGHT
DISCREPANCIES IN MODELS AFTER TAU 48 CONTRIBUTE TO A 150 NM
CROSS-TRACK SPREAD AND A 180 NM ALONG-TRACK SPREAD AT TAU 120. AS A
RESULT, THE JTWC TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE FROM
TAU 0-72 AND MEDIUM CONFIDENCE FROM TAU 72-120. RELIABLE INTENSITY
GUIDANCE IS IN STRONG AGREEMENT OF RAPID INTENSIFICATION THROUGH
TAU 48. NEARLY EVERY RAPID INTENSIFICATION AID (RIPA, RIDE, RICN, 
FRIA) ARE INITIATED, WHICH SUPPORTS THE NEAR-TEERM RAPID 
INTENSIFICATION FORECAST WITH HIGH CONFIDENCE. AFTER TAU 48, MODELS 
DISAGREE ON THE RATE AT WHICH 31W WILL WEAKEN WHILE INTERACTING WITH 
LAND. AS A RESULT, THERE IS A LARGE SPREAD IN THE INTENSITY AND 
REINTENSIFICATION FOLLOWING REEMERGENCE OVER WATER, INCLUDING THE PEAK 
INTENSITY. CONSEQUENTLY, THE JTWC INTENSITY FORECAST IS ASSESSED WITH 
OVERALL HIGH CONFIDENCE FROM TAU 0-72 AND OVERALL MEDIUM CONFIDENCE 
FROM TAU 72-120.

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