WDIO31 PGTW 072100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 02A (BIPARJOY) WARNING 
NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.8N 65.9E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 568 NM SOUTHEAST OF MASIRAH ISLAND
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
COMPACT CIRCULATION OBSCURED BY A CENTRAL DENSE OVERCAST (CDO). THE
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
071740Z ASCAT PASS. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON A COMBINATION OF OBJECTIVE AND SUBJECTIVE
INTENSITY ESTIMATES. THE SYSTEM IS MOVING TOWARD THE NORTHWEST ON
THE WESTERN PERIPHERY OF AN EXTENSION OF THE SUBTROPICAL RIDGE
(STR) OVER INDIA. ENVIRONMENTAL ANALYSIS IS ASSESSED AS MARGINALLY
FAVORABLE, WITH GOOD MODERATE POLEWARD AND EQUATORWARD OUTFLOW
ALOFT, MODERATE EASTERLY VERTICAL WIND SHEAR (VWS) WHICH IS TILTING
THE SYSTEM WESTWARD, AND VERY WARM SEA SURFACE TEMPERATURES (SSTS)
RANGING (31-32C).

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: AN EXTENSION OF THE SUBTROPICAL RIDGE
(STR) OVER INDIA AND A NEAR-EQUATORIAL RIDGE (NER) TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   KNES: T4.0 - 65 KTS
   DEMS: T4.0 - 65 KTS
   CIMSS SATCON: 72 KTS AT 071300Z
   CIMSS ADT: 77 KTS AT 071800Z

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

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: 02A CONTINUES TO TRACK NORTH-NORTHWESTWARD AS
A SHORTWAVE TROUGH PASSES TO THE NORTH WHILE A RIDGE BUILDS OVER
INDIA. BY TAU 24, THE SYSTEM WILL PICK UP SPEED AS THE RIDGE OVER
INDIA IS EXPECTED TO BECOME THE DOMINANT STEERING FEATURE. AFTER
TAU 48, 02A WITH TRACK NORTHWESTWARD THROUGH THE REMAINDER OF THE
FORECAST, AS THE RIDGE STRENGTHENS AND ELONGATES TO A
NORTHWEST-SOUTHEAST ORIENTATION. DUE TO THE FAVORABLE ENVIRONMENTAL
FACTORS, 02A IS FORECAST TO INTENSIFY TO A PEAK OF 90-95 KNOTS OVER
THE NEXT 12-24 HOURS. HOWEVER, AFTER TAU 36, THE SYSTEM IS EXPECTED
TO STEADILY WEAKEN DUE TO MULTIPLE NEGATIVE FACTORS, SUCH AS
INCREASING VWS, AND DECREASED OUTFLOW ALOFT. AFTER TAU 72, FURTHER
WEAKENING IS EXPECTED AS A RESULT OF DRY AIR ENTRAINMENT.

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE
CONTINUES TO SHOW A BIFURCATION, BETWEEN GFS, NAVGEM, AND THE GFS
ENSEMBLE MEAN ON THE WESTERN PERIPHERY OF THE GUIDANCE ENVELOPE
TURNING TOWARD THE ARABIAN PENINSULA. WHILE THE UKMET, GALWEM, AND
ECMWF TRACKING THE SYSTEM NORTH AND ON THE RIGHT OF THE GUIDANCE
ENVELOPE. CROSS-TRACK SPREAD AT TAU 72 IS ROUGHLY 230NM, INCREASING
TO 315NM AT TAU 120. ENSEMBLE MEMBERS FOR BOTH GFS AND ECMWF ALSO
SHOW A HIGH DEGREE OF UNCERTAINTY WITH LARGE SPREAD. THE JTWC
FORECAST IS PLACED WITH LOW CONFIDENCE BASED ON THE UNCERTAINTY IN
THE TRACK GUIDANCE. THE TRACK REMAINS CLOSE TO THE CONSENSUS MEAN
THROUGH TAU 120, AND HEDGED SLIGHTLY TO THE WEST OF CONSENSUS AND
MORE IN LINE WITH THE GFS, NAVGEM, AND GFS ENSEMBLE SOLUTIONS.
INTENSITY GUIDANCE IS MIXED, WITH HWRF SHOWING AN INTENSIFICATION
PHASE UP TO 95 KNOTS AND CTCI UP TO 105 KNOTS. WHILE GFS AND DSHN
REPRESENT THE LOW END OF THE INTENSITY GUIDANCE ENVELOPE, WITH A
PEAK OF 80 KNOTS. THEREFORE THE JTWC INTENSITY FORECAST IS PLACED
WITH LOW CONFIDENCE AND CLOSE TO THE MULTI-MODEL CONSENSUS. 


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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