WDPN31 PGTW 020900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 31W (KALMAEGI) WARNING 
NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.3N 133.3E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 746 NM EAST-SOUTHEAST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM 31W (KALMAEGI) WITH VIGOROUS BURSTS OF DEEP CONVECTION OVER
THE CENTER AND A LARGE BANDING FEATURE WITHIN THE NORTHERN
PERIPHERY. A 020455Z AMSR2 MICROWAVE IMAGE SUITE REVEALED A COMPACT
CORE WITH A SMALL MICROWAVE EYE AND DEEP CONVECTION SLIGHTLY OFFSET
TO THE SOUTH. 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. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON EXTRAPOLATION FROM THE AFOREMENTIONED
AMSR2 MICROWAVE IMAGE. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND CIMSS
OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

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: T2.5 - 35 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 47 KTS AT 020600Z
   CIMSS ADT: 47 KTS AT 020600Z
   CIMSS AIDT: 41 KTS AT 020600Z
   CIMSS D-PRINT: 48 KTS AT 020600Z

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 COMBINED INFLUENCE OF SUBTROPICAL RIDGES
TO BOTH THE NORTHEAST AND NORTHWEST. AN INITIAL LANDFALL IS
FORECAST TO OCCUR AROUND TAU 36 NEAR SOUTHERN SAMAR AND LEYTE.
AFTER TAU 36, THE TRACK IS EXPECTED TO TURN MORE 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.  REGARDING INTENSITY,
31W IS FORECAST TO RAPIDLY INTENSIFY OVER THE NEXT 36 HOURS,
LEADING UP TO LANDFALL IN THE PHILIPPINES. VERY WARM SEA SURFACE
TEMPERATURES, HIGH OHC VALUES, AND ROBUST OUTFLOW WILL AID IN THE
INTENSIFICATION OF THE STORM. AN INTENSITY OF AROUND 95 KTS IS
FORECAST NEAR THE TIME OF LANDFALL, WHICH IS EXPECTED TO BE CLOSE
TO TACLOBAN CITY. 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 50 NM CROSS-TRACK SPREAD NEAR THE TIME
OF LANDFALL, 65 NM AT TAU 72, AND 130 NM AT TAU 120. THIS TIGHT
ENVELOPE IN GUIDANCE LENDS HIGH CONFIDENCE TO THE JTWC TRACK
FORECAST THROUGHOUT THE FORECAST PERIOD. THERE IS QUITE A BIT MORE
UNCERTAINTY WHEN IT COMES TO INTENSITY. NEARLY ALL AVAILABLE RAPID
INTENSIFICATION AIDS ARE TRIGGERED THIS MODEL RUN. MESOSCALE MODEL
INTENSITIES AT TAU 36 RANGE FROM 75 KTS (HWRF) TO 95 KTS (HAFS-A)
WHILE SOME OF THE RAPID INTENSIFICATION AIDS SUGGEST AN EVEN HIGHER
PEAK. MODELS THEN AGREE ON SLIGHT WEAKENING THROUGH TAU 48 AND THEN
REINTENSIFICATION THROUGH TAU 96. THE PEAK WITHIN THE SOUTH CHINA
SEA RANGES FROM 90-110 KTS WITH HAFS-A BEING THE MOST AGGRESSIVE
MODEL. THE JTWC INTENSITY FORECAST IS PLACED SLIGHTLY HIGHER THAN
THE CONSENSUS WITH OVERALL 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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