WDPN31 PGTW 181500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (IN-FA) WARNING NR 
010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.0N 132.0E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 311 NM SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS AN EXPOSED
LOW-LEVEL CIRCULATION CENTER (LLCC) POSITIONED ALONG THE WESTERN
EDGE OF A LARGE AREA OF DEEP CONVECTION. AN 181230Z 89GHZ GPM
MICROWAVE IMAGE INDICATES SHALLOW BANDING WRAPPING TIGHTLY INTO A
WELL-DEFINED LLCC WITH IMPROVED DEEP CONVECTIVE BANDING OVER THE
EASTERN SEMICIRCLE, WHICH SUPPORTS THE INITIAL POSITION WITH HIGH
CONFIDENCE. THE INITIAL INTENSITY OF 40 KTS IS BASED ON AN AVERAGE
OF THE PGTW AND KNES DVORAK ESTIMATES AND IS CONSISTENT WITH THE
191026Z ASCAT-A DATA. ENVIRONMENTAL ANALYSIS INDICATES MARGINALLY
FAVORABLE CONDITIONS WITH GRADUALLY IMPROVING POLEWARD OUTFLOW OVER
THE WESTERN SEMICIRCLE AS THE UPPER LOW TO THE NORTH-NORTHWEST
WEAKENS AND SHIFTS POLEWARD INTO THE WEST SEA. ALTHOUGH MID-LEVEL
DRY AIR ENTRAINMENT AND VERTICAL WIND SHEAR (VWS) CONTINUE TO
HINDER CONVECTIVE DEVELOPMENT OVER THE LLCC, EQUATORWARD OUTFLOW
REMAINS ROBUST WITH WARM SST VALUES.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) CENTERED OVER
HONSHU EXTENDING SOUTHWARD OVER THE NORTHEASTERN AND EASTERN
PERIPHERY OF THE SYSTEM.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 32 KTS AT 181140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD
   OTHER FACTORS: MID-LEVEL DRY AIR ENTRAINMENT


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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: BASED ON THE IMPROVED MODEL GUIDANCE 
ENVELOPE THROUGH TAU 72, THE JTWC FORECAST TRACK HAS SHIFTED SOUTH 
FROM THE PREVIOUS WARNING. HOWEVER, EXPANSIVE GALE-FORCE WINDS AND 
POSSIBLE STORM-FORCE WINDS ARE STILL EXPECTED OVER THE OKINAWA 
REGION. 

FORECAST DISCUSSION: UPPER-AIR SOUNDINGS FROM NAZE (47909) PROVIDE
CLEAR EVIDENCE THAT THE STR IS BUILDING NORTH OF THE SYSTEM; OVER
THE PAST DAY STEERING LEVEL WINDS HAVE BACKED FROM SOUTHWESTERLY
(DUE TO THE UPPER LOW) TO EAST-SOUTHEASTERLY TO SOUTHEASTERLY AS
DEPICTED IN THE 181200Z NAZE SOUNDING. CONSEQUENTLY, TS 09W HAS
SLOWED AND IS TURNING NORTHWESTWARD. THE SYSTEM IS EXPECTED TO
TRACK WEST-NORTHWESTWARD TO WESTWARD ALONG THE SOUTHERN PERIPHERY
OF THE STR THROUGH THE FORECAST PERIOD. THE DEEP UPPER LOW IN THE
WEST SEA CONTINUES TO FILL AND DRIFT POLEWARD, AND IS NOW ENHANCING
POLEWARD OUTFLOW ALLOWING TS 09W TO CONSOLIDATE. DESPITE SOME
MID-LEVEL DRY AIR ENTRAINMENT OVER THE WESTERN SEMICIRCLE, TS 09W
SHOULD SLOWLY INTENSIFY THROUGH TAU 24. AFTER TAU 24, ENVIRONMENTAL
CONDITIONS SHOULD GRADUALLY IMPROVE ALLOWING THE SYSTEM TO VENT AND
SUSTAIN MORE CENTRALIZED DEEP CONVECTION, WHICH WILL MOISTEN THE
MID-LEVELS. THIS SHOULD LEAD TO A FASTER RATE OF INTENSIFICATION
WITH A PEAK OF 85 KNOTS ANTICIPATED BY TAU 96. AFTER TAU 96,
INTERACTION WITH TAIWAN WILL WEAKEN THE SYSTEM.   

MODEL DISCUSSION: THERE IS INCREASING CONFIDENCE IN THE TRACK
FORECAST THROUGH TAU 72 WITH MEDIUM CONFIDENCE; AT TAU 72 THERE IS
AN 85NM SPREAD IN NUMERICAL MODEL GUIDANCE, WHICH SUPPORTS THE SHIFT 
IN THE JTWC FORECAST TRACK SOUTH SINCE THE PREVIOUS FORECAST. AFTER 
TAU 72, MODEL GUIDANCE DIVERGES WITH A LARGE SPREAD AND LOW 
CONFIDENCE DUE TO POTENTIAL DIRECT CYCLONE INTERACTION WITH INVEST 
99W, WHICH IS EXPECTED TO GRADUALLY STRENGTHEN OVER THE NEXT FEW 
DAYS. THERE IS LOW CONFIDENCE IN THE JTWC INTENSITY FORECAST WITH A 
LARGE SPREAD IN INTENSITY GUIDANCE.  

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