WDPN31 PGTW 232100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 06W (CHAMPI) WARNING NR 
012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.7N 140.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 313 NM WEST OF AGRIHAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ENHANCED IR SATELLITE IMAGERY INDICATES THAT THE CYCLONE HAS BECOME
BETTER ORGANIZED SINCE 24 HOURS AGO, WITH DEEP CONVECTIVE BANDS IN
THE EASTERN SEMICIRCLE AND A MORE CONSOLIDATED MASS OF DEEP
CONVECTION OBSCURING THE LOW-LEVEL CENTER (LLC). ANIMATED 7.3
MICROMETER IMAGERY FROM HIMAWARI-8 INDICATES THAT DRY LOW TO
MID-LEVEL AIR REMAINS CLOSE BY IN THE WESTERN SEMICIRCLE. HOWEVER,
THE PAST 24 HOURS OF LOW VERTICAL SHEAR SEEM TO HAVE ALLOWED A
SMALL ENVELOPE OF MOISTURE TO WRAP AROUND THE LLC AS DRY AIR IS
MIXED OUT, FACILITATING THE DEVELOPMENT OF CENTRAL CONVECTION. THE
CYCLONE IS COCOONED IN A SMALL BUBBLE OF LOW VERTICAL SHEAR BETWEEN
AN UPPER-LEVEL LOW TO THE NORTHEAST AND A BELT OF UPPER-LEVEL
NORTHEASTERLY FLOW JUST TO THE NORTHWEST. THIS CONTINUES TO
RESTRICT RADIAL OUTFLOW, BUT THE EQUATORWARD CHANNEL IN THE
SOUTHEAST QUADRANT HAS IMPROVED SINCE YESTERDAY. THE LLC HAS BEEN
DIFFICULT TO LOCATE DURING THE PAST 12 HOURS IN THE ABSENCE OF
SCATTEROMETER DATA, THUS THERE IS LOW CONFIDENCE IN THE INITIAL
POSITION. THE CURRENT INTENSITY HAS BEEN LOWERED SLIGHTLY TO 35 KT
IN AGREEMENT WITH AGENCY DVORAK FIXES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: DRY LOW TO MID-LEVEL AIR MASS TO THE WEST AND
SOUTH

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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: TROPICAL STORM 06W (CHAMPI) WILL CONTINUE
TRACKING NORTHWARD DURING THE NEXT 48 HOURS AS IT ROUNDS THE
PERIPHERY OF THE SUBTROPICAL RIDGE TO THE EAST. THEREAFTER, A
GRADUAL TURN NORTHEASTWARD IS EXPECTED AS THE CYCLONE NEARS THE
BAIU FRONTAL BOUNDARY SOUTHEAST OF JAPAN. EXTRATROPICAL TRANSITION
WILL OCCUR BY 96 HOURS AS CHAMPI'S CIRCULATION BECOMES ABSORBED
INTO THE BAIU BOUNDARY WHILE TRACKING OVER COOL SEA SURFACE
TEMPERATURES (SST) OF 21-24C TO THE EAST OF HONSHU. THE JTWC TRACK
FORECAST IS A LITTLE SLOWER THAN THE PREVIOUS FORECAST AS MODEL
GUIDANCE COMES INTO BETTER ALIGNMENT ON THE TIMING OF THE
NORTHEASTWARD TURN. THE JTWC INTENSITY FORECAST CALLS FOR STEADY
INTENSIFICATION TO A PEAK OF 65 KT IN ABOUT 48 HOURS AS LOW TO
MODERATE SHEAR PERSISTS, WHICH SHOULD ALLOW AN INNER CONVECTIVE
CORE TO ORGANIZE. PERIODIC INGESTION OF DRY AIR AND LIMITED OUTFLOW
IS LIKELY TO LIMIT INTENSIFICATION TO SOME EXTENT. AFTER 48 HOURS,
THE CYCLONE WILL PASS INTO COOLER WATERS OF 24-25C, AND INTERACTION
WITH THE BAIU FRONTAL BOUNDARY WILL INCREASE VERTICAL SHEAR. THESE
FACTORS WILL LEAD TO WEAKENING TO 45 KT BY THE TIME OF
EXTRATROPICAL TRANSITION IN 96 HOURS. IT IS WORTH NOTING THAT THE
CYCLONE'S COMPACT SIZE MAKES IT SUSCEPTIBLE TO QUICK CHANGES IN
INTENSITY EITHER UP OR DOWN, AND THERE IS THUS ONLY MEDIUM
CONFIDENCE IN THE INTENSITY FORECAST.

MODEL DISCUSSION: THE JTWC FORECAST LIES SLIGHTLY TO THE RIGHT OF
THE MULTI-MODEL CONSENSUS, TRACKING BETWEEN ECMWF AND GFS,
DISCOUNTING THE LEFTWARD OUTLIER AFUM. THE JTWC INTENSITY FORECAST
IS SLIGHTLY BELOW THE MULTI-MODEL CONSENSUS, LARGELY DUE TO CURRENT
TRENDS BEING UNSUPPORTIVE OF THE RAPID RATE OF INTENSIFICATION IN
THE GUIDANCE DURING THE FIRST 12 HOURS.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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