WDPN31 PGTW 021500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 31W (KALMAEGI) WARNING 
NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.3N 131.8E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 662 NM EAST-SOUTHEAST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM 31W (KALMAEGI) WITH TWO DISTINCT CLUSTERS OF DEEP CONVECTION
CREATING AN OBLONG CENTRAL DENSE OVERCAST (CDO) OVER THE
CIRCULATION. THE LOW-LEVEL CIRCULATION CENTER (LLCC) IS ANALYZED TO
BE UNDERNEATH THE SOUTHEASTERN LOBE OF CONVECTION, WHICH IS
CONFIRMED BY A 021141Z GMI 37 GHZ MICROWAVE IMAGE. THE GMI
MICROWAVE IMAGE ALSO REVEALED THE HIGHLY COMPACT CORE WITH A SMALL
MICROWAVE EYE FEATURE, SUPPORTING THE INITIAL POSITION WITH HIGH
CONFIDENCE. THE INITIAL INTENSITY OF 55 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND CIMSS OBJECTIVE
INTENSITY ESTIMATES LISTED BELOW. ENVIRONMENTAL ANALYSIS INDICATES
THAT 31W IS IN A HIGHLY FAVORABLE ENVIRONMENT CHARACTERIZED BY
STRONG RADIAL OUTFLOW ALOFT, LOW (10-15 KTS) EASTERLY VERTICAL WIND
SHEAR, AND WARM (29-30 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: COMBINED STEERING INFLUENCE OF A LARGE
SUBTROPICAL RIDGE CENTERED FAR TO THE NORTHEAST AND A SMALLER
SUBTROPICAL RIDGE CENTERED SOUTHWEST OF TAIWAN.

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: 55 KTS AT 021200Z
   CIMSS AIDT: 44 KTS AT 021200Z
   CIMSS D-PRINT: 40 KTS AT 021240Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL

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: 31W IS FORECAST TO TRACK GENERALLY WESTWARD
THROUGH TAU 36, UNDER THE INFLUENCE OF EXTENSIONS OF SUBTROPICAL
RIDGES TO BOTH THE NORTHEAST AND NORTHWEST. AN INITIAL LANDFALL IS
FORECAST TO OCCUR AROUND TAU 30 NEAR TACLOBAN CITY. AFTER TAU 36,
THE TRACK IS EXPECTED TO TURN NORTHWESTWARD AS THE RIDGE SOUTHWEST OF 
TAIWAN BECOMES THE PRIMARY STEERING MECHANISM. 31W WILL THEN TRACK 
THROUGH THE SOUTH CHINA SEA BEFORE MAKING A FINAL LANDFALL IN CENTRAL 
VIETNAM JUST AFTER TAU 96. REGARDING INTENSITY, 31W IS FORECAST TO 
RAPIDLY INTENSIFY OVER THE NEXT 24-30 HOURS, LEADING UP TO LANDFALL 
IN THE PHILIPPINES. VERY WARM SEA SURFACE TEMPERATURES, HIGH OHC 
VALUES, AND ROBUST OUTFLOW WILL SUPPORT THE INTENSIFICATION OF THE 
STORM. AN INTENSITY OF 90 KTS IS FORECAST FOR TAU 24, BUT AN EVEN 
HIGHER PEAK JUST BEFORE LANDFALL IS LIKELY TO OCCUR. KALMAEGI WILL 
THEN BRIEFLY WEAKEN AS IT TRACKS ACROSS THE VISAYAS. HOWEVER, THE 
INTENSIFICATION TREND WILL CONTINUE ONCE THE VORTEX EMERGES WITHIN 
THE SOUTH CHINA SEA. STRONG EQUATORWARD OUTFLOW AND WARM SEA SURFACE 
TEMPERATURES WILL ALLOW FOR A SECOND PEAK OF AROUND 105 KTS BEFORE 
LANDFALL IN VIETNAM. RUGGED TERRAIN INTERACTION WILL RAPIDLY WEAKEN 
THE SYSTEM AS IT TRACKS THROUGH VIETNAM AND INTO SOUTHERN LAOS.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE CONTINUES TO BE IN
VERY STRONG AGREEMENT WITH A 40 NM CROSS-TRACK SPREAD NEAR THE TIME
OF LANDFALL, 60 NM AT TAU 72, AND 150 NM AT TAU 120. THIS TIGHT
ENVELOPE IN GUIDANCE LENDS HIGH CONFIDENCE TO THE JTWC TRACK
FORECAST THROUGHOUT THE FORECAST PERIOD. THERE IS A BIT MORE
UNCERTAINTY WHEN IT COMES TO INTENSITY WITH MANY RAPID
INTENSIFICATION (RI) AIDS CONTINUING TO TRIGGER. HOWEVER, HAFS-A
AND HWRF ARE IN A BIT BETTER AGREEMENT NOW WITH INTENSITIES AT TAU
24 RIGHT AROUND 90-95 KTS (IN LINE WITH THE RI AIDS). THE JTWC
INTENSITY FORECAST FOLLOWS THIS BULK OF GUIDANCE AND CONTINUES TO
CALL FOR RI BEFORE LANDFALL IN THE PHILIPPINES. MODELS AGREE ON
SLIGHT WEAKENING THROUGH TAU 48 AND THEN REINTENSIFICATION THROUGH
TAU 96 WITHIN THE SOUTH CHINA SEA. MESOSCALE MODELS PREDICT THE
SECOND PEAK TO BE 105-115 KTS WITH COAMPS-TC BEING THE MOST
AGGRESSIVE MODEL THIS RUN. THE JTWC INTENSITY FORECAST IS PLACED
SLIGHTLY HIGHER THAN THE CONSENSUS WITH MEDIUM CONFIDENCE.

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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