WDPN31 PGTW 210900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 09W (IN-FA) WARNING NR 021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.2N 127.3E
   INITIAL INTENSITY: 95 KTS
   GEOGRAPHIC REFERENCE: 141 NM SOUTH OF KADENA AB
   MOVEMENT PAST 6 HOURS: WESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 42 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED RADAR IMAGERY FROM OKINAWA AND SATELLITE IMAGERY CONTINUE
TO SHOW A CLEAR, 25 NM WIDE EYE WITH AN EYEWALL THAT HAS BEEN
PERIODICALLY BROKEN IN THE EASTERN SEMICIRCLE DURING THE PAST SIX
HOURS. A BELT OF DRY AIR WRAPPING FROM THE NORTHWEST QUADRANT
AROUND THE SOUTHERN SEMICIRCLE CAN BE SEEN ERODING CONVECTION TO
SOME EXTENT ON THE EASTERN SIDE OF THE CIRCULATION. UPPER-LEVEL
OUTFLOW IS EXPANDING FREELY IN ALL QUADRANTS EXCEPT SOUTHEASTERN.
THE INITIAL INTENSITY IS HELD STEADY AT 95 KT BASED ON A BLEND OF
AGENCY DVORAK INTENSITY ESTIMATES. SUSTAINED TROPICAL STORM FORCE
WINDS OF 34 KT WITH GUSTS OF 42 KT WERE RECENTLY REPORTED AT KADENA
AIR BASE, OKINAWA.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYER RIDGE OVER THE SEA OF JAPAN

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T5.0 - 90 KTS
   KNES: T5.5 - 102 KTS
   CIMSS ADT: 109 KTS AT 210540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: BELT OF DRY AIR WRAPPING AROUND WESTERN AND
SOUTHERN SEMICIRCLES AND DYNAMIC OCEAN COOLING INDUCED BY SLOW
FORWARD MOTION

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: TYPHOON 09W (IN-FA) IS EXPECTED TO CONTINUE
TRACKING SLOWLY WESTWARD FOR THE NEXT 36 HOURS IN A WEAK STEERING
ENVIRONMENT, AS THE TYPHOON IS CAUGHT BETWEEN THE MONSOONAL
WESTERLIES TO THE SOUTH AND A LOW-MID LEVEL RIDGE ANCHORED OVER THE
SEA OF JAPAN. THIS RIDGE IS THE DOMINANT STEERING INFLUENCE, AND IS
GUIDING THE TYPHOON WESTWARD AROUND ITS SOUTHERN PERIPHERY. A TURN
TO THE NORTHWEST IS EXPECTED AFTER 36 HOURS AS THE TYPHOON ROUNDS
THE SOUTHWESTERN PERIPHERY OF THE RIDGE AND AN UPPER-LEVEL TROUGH
DIGS OVER EASTERN CHINA. NUMERICAL MODEL GUIDANCE HAS SHIFTED TO
THE RIGHT, AND THE JTWC TRACK FORECAST HAS ACCORDINGLY BEEN SHIFTED
TO THE RIGHT AFTER 24 HOURS, BUT STILL LIES ON THE LEFT-HAND SIDE
OF THE GUIDANCE ENVELOPE. THE NORTHWESTWARD TRACK IS EXPECTED TO
CARRY TYPHOON IN-FA INTO EASTERN CHINA BETWEEN 72 AND 96 HOURS TO
THE SOUTH OF SHANGHAI. THE TYPHOON'S INTENSITY IS CURRENTLY BEING
LIMITED BY DRY AIR ENTRAINMENT AND THE LIKELIHOOD OF SOME DYNAMIC
OCEAN COOLING BENEATH THE CIRCULATION, AS INDICATED BY COUPLED
OCEAN ANALYSES FROM THE HWRF AND COAMPS-TC MODELS. OCEAN ANALYSIS
INDICATES THAT TYPHOON IN-FA IS CURRENTLY PASSING OVER A COOL EDDY
LOCATED SOUTH OF OKINAWA, AND WILL MOVE OVER A DEEPER LAYER OF WARM
WATER DURING THE NEXT 36 HOURS. THE JTWC INTENSITY FORECAST THUS
CALLS FOR SLIGHT INTENSIFICATION DURING THE NEXT 36 HOURS TO A PEAK
INTENSITY OF 105 KT. THEREAFTER, PROXIMITY TO TAIWAN IS EXPECTED TO
DISRUPT THE MONSOONAL INFLOW CHANNEL, WHICH COMBINED WITH SLIGHTLY
SHALLOWER WARM WATER IS EXPECTED TO INDUCE GRADUAL WEAKENING AS
IN-FA APPROACHES CHINA.

MODEL DISCUSSION: THE JTWC TRACK FORECAST LIES SLIGHTLY TO THE LEFT
OF THE MULTI-MODEL CONSENSUS, AND THE INTENSITY FORECAST IS CLOSE
TO THE MULTI-MODEL CONSENSUS.

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