WDIO31 PGTW 081500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 02A (BIPARJOY)   
WARNING NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.4N 66.0E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 547 NM SOUTHEAST OF MASIRAH ISLAND
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 02 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). UNFORTUNATELY, THERE HAS BEEN A
LACK OF DECENT MICROWAVE IMAGERY OVER THE PAST SIX HOURS THUS THERE
IS LOW CONFIDENCE IN THE INITIAL POSITION, WHICH IS PLACED ALONG
THE EASTERN EDGE OF THE CDO FEATURE AND THE EASTERN EDGE OF THE CORE 
CONVECTION IN THE LOW-RESOLUTION ATMS 88.2GHZ MICROWAVE IMAGE. FOR 
NOW, THE INITIAL INTENSITY IS CONSERVATIVELY HELD AT 75 KTS WITH 
MEDIUM CONFIDENCE BASED ON THE PGTW AND KNES DVORAK CURRENT INTENSITY 
ESTIMATES.

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 SATCON: 74 KTS AT 080913Z
   CIMSS ADT: 72 KTS AT 081300Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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 MEANDERING SLOWLY
POLEWARD UNDER THE WEAK STEERING INFLUENCE OF THE STR TO THE EAST
AND WILL CONTINUE TO TRACK SLOWLY POLEWARD THROUGH TAU 72 THEN
NORTH-NORTHWESTWARD THROUGH TAU 120. AS VERTICAL WIND SHEAR RELAXES, 
THE SYSTEM IS EXPECTED TO INTENSIFY 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 THE
GULF OF 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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