WDIO31 PGTW 080900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 02A (BIPARJOY)  
WARNING NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.2N 66.1E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 559 NM SOUTHEAST OF MASIRAH ISLAND
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 27 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION (LLC) WITH A CENTRAL DENSE
OVERCAST (CDO) FEATURE OBSCURING THE WESTERN HALF OF THE LLC. THE MSI 
ALSO CLEARLY SHOWS EASTERLY PRESSURE ON THE SYSTEM WITH WESTWARD 
OUTFLOW DOMINATING ASSOCIATED WITH LOW TO MODERATE (15-20 KNOT) 
VERTICAL WIND SHEAR (VWS). A 080651Z GMI 89GHZ MICROWAVE IMAGE ALSO 
REVEALS A 15 TO 20NM WESTWARD TILT WITH A COMPACT CORE AND SMALL 
MICROWAVE EYE FEATURE SEPARATED FROM THE PRIMARY SPIRAL BANDING OVER 
THE WESTERN AND SOUTHERN SEMICIRCLE. OVERALL, THERE IS MEDIUM 
CONFIDENCE IN THE INITIAL POSITION BASED ON THE MSI AND GMI. THE 
INITIAL INTENSITY OF 75 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED 
ON THE PGTW AND KNES DVORAK ESTIMATES, AND REFLECTS A SLIGHT 
WEAKENING TREND OVER THE PAST SIX HOURS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: COMPLEX: A WEAK, NARROW SUBTROPICAL
RIDGE (STR) IS POSITIONED TO THE EAST WITH ANOTHER STR LOCATED OVER
THE SOUTHERN ARABIAN PENINSULA 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   KNES: T4.5 - 77 KTS
   CIMSS ADT: 79 KTS AT 080600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 31-32 CELSIUS
   OUTFLOW: MODERATE WESTWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TROPICAL CYCLONE (TC) 02A IS TRACKING SLOWLY
POLEWARD UNDER THE WEAK STEERING INFLUENCE OF THE STR TO THE EAST
AND WILL TRACK POLEWARD THROUGH TAU 72 THEN NORTH-NORTHWESTWARD
THROUGH TAU 120. THE SYSTEM IS EXPECTED TO INTENSIFY GRADUALLY TO
100 KNOTS BY TAU 36. AFTER TAU 36, PERSISTENT UPPER-LEVEL
EASTERLIES AND MODERATE TO HIGH VERTICAL WIND SHEAR WILL PREVAIL
AND WEAKEN THE SYSTEM STEADILY. 

MODEL DISCUSSION: AS MENTIONED EARLIER, THE STEERING PATTERN IS
WEAK AND COMPLEX WITH COMPETING STEERING INFLUENCES AND A VERY
LARGE SPREAD IN DETERMINISTIC AND PROBABILISTIC GUIDANCE. THE ECMWF
ENSEMBLE (EPS) FAVORS A SLOW POLEWARD TRACK WHILE THE GFS ENSEMBLE
(GEFS) FAVORS A SLOW NORTHWESTWARD TO NORTH-NORTHWESTWARD TRACK.
SIMILARLY, THE GFS DETERMINISTIC TRACKER IS MORE INFLUENCED BY THE
STR OVER THE ARABIAN PENINSULA SO IS TURNING THE SYSTEM TOWARD OMAN
WHILE ECMWF IS MORE INFLUENCED BY THE EASTERN STR. EITHER SCENARIO
IS VIABLE THUS THERE IS LOW CONFIDENCE (HIGH UNCERTAINTY) IN THE
DAY 3 TO DAY 5 FORECAST PERIOD.  

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