WDIO31 PGTW 090300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 02A (BIPARJOY) WARNING 
NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.6N 66.6E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 566 NM SOUTHEAST OF MASIRAH ISLAND
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS LITTLE CHANGE
IN VORTEX STRUCTURE DURING THE PAST 6 HOURS. A PERSISTENT MASS OF
DEEP CONVECTION CONTINUES TO OBSCURE THE LOW-LEVEL CIRCULATION
CENTER (LLCC), WHICH APPEARS TO BE UNDER THE EASTERN SIDE OF THE
CONVECTION DUE TO CONTINUING MODERATE-STRONG EASTERLY SHEAR, THOUGH
THERE IS LOW CONFIDENCE IN THE EXACT POSITION DUE TO A LACK OF
MICROWAVE AND SURFACE VECTOR WIND DATA DURING THE PAST 10 HOURS.
SATELLITE-BASED INTENSITY ESTIMATES HAVE FALLEN RELATIVE TO 6 HOURS
AGO, AND THE CURRENT INTENSITY IS ACCORDINGLY ADJUSTED DOWNWARD TO
65 KT. DEEP CONVECTION APPEARS TO BE ATTEMPTING TO WRAP FURTHER
UPSHEAR DURING THE LAST COUPLE OF HOURS, BUT IS NOT A SUSTAINED
TREND YET.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: UPPER-LEVEL RIDGE TO THE NORTH AND
LOW-LEVEL MONSOONAL SOUTHWESTERLIES TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   KNES: T4.5 - 77 KTS
   CIMSS SATCON: 54 KTS AT 082147Z
   CIMSS ADT: 53 KTS AT 090000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-30 KTS
   SST: 31-32 CELSIUS
   OUTFLOW: MODERATE WESTWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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: TROPICAL CYCLONE 02A (BIPARJOY) CONTINUES TO
BATTLE MODERATE TO STRONG EASTERLY SHEAR, IMPOSED BY THE
JUXTAPOSITION OF LOW-LEVEL MONSOONAL SOUTHWESTERLIES WITH MID TO
UPPER-LEVEL EASTERLIES. THIS PREVAILING ENVIRONMENT IS EXPECTED TO
PERSIST THROUGHOUT THE FORECAST PERIOD, AND IS THE SOURCE OF
CONSIDERABLE UNCERTAINTY IN BOTH THE TRACK AND INTENSITY FORECASTS.
THE MODELS WHICH STRENGTHEN BIPARJOY MOST (GFS, GFS ENSEMBLE MEAN,
AND HWRF) KEEP THE STORM MOVING WEST OF NORTH IN THE SHORT TERM DUE
TO A DEEPER VORTEX AFFECTED MORE BY UPPER-LEVEL EASTERLY FLOW. THIS
NORTHWESTWARD MOTION THEN SNOWBALLS AS THE STORM COMES UNDER THE
INFLUENCE OF THE MID-LEVEL RIDGE OVERLYING SAUDI ARABIA AND THE
PERSIAN GULF IN 72-96 HOURS. OTHER MODELS SUCH AS ECMWF, ECMWF
ENSEMBLE, AND UKMET GENERALLY SHOW A WEAKER VORTEX IN THE SHORT
TERM WHICH TRACKS EAST OF NORTH UNDER THE INFLUENCE OF THE
LOW-LEVEL MONSOONAL SOUTHWESTERLIES, ULTIMATELY TRACKING TOWARDS
NORTHWEST INDIA AND PAKISTAN. IN GENERAL, THE TOTALITY OF MODEL
GUIDANCE CONTINUES TO SHIFT EASTWARD. EVEN THE GFS NOW TRACKS
TOWARD PAKISTAN, ALONG WITH A SIGNIFICANT MINORITY OF GFS ENSEMBLE
MEMBERS. WHICH GROUP OF MODELS IS CORRECT DEPENDS ON A
DELICATE BALANCE OF THE STORM'S INTENSITY AND THE TUG-OF-WAR
BETWEEN THE TWO OPPOSING STEERING FLOWS. THE PAST 12 HOURS OF
FORWARD MOTION SUGGEST THAT BIPARJOY IS NOT MOVING AS FAR WEST
AS GFS AND HWRF HAD EXPECTED, LENDING CREDENCE TO MODELS ON THE
RIGHT-HAND SIDE OF THE GUIDANCE ENVELOPE. THE CURRENT FORECAST IS
SHIFTED ANOTHER 30-40 NM EAST OF THE PREVIOUS FORECAST, AND
UNCERTAINTY REMAINS HIGHER THAN AVERAGE FOR NOW. THE INTENSITY
FORECAST IS ALSO UNCERTAIN DUE TO THE HIGH SHEAR ASSAULTING THE
STORM IN AN OTHERWISE FAVORABLE ENVIRONMENT WITH VERY WARM SEA
SURFACE TEMPERATURES. THE JTWC FORECAST CONTINUES TO SHOW A PERIOD
OF GRADUAL INTENSIFICATION DURING THE NEXT 36-48 HOURS DUE TO A
MOMENTARY DECREASE IN WIND SHEAR CURRENTLY EXPECTED BY SOME MODELS,
FOLLOWED BY A LEVELING OFF AND GRADUAL WEAKENING AS SHEAR INCREASES
ANEW AFTER 48 HOURS. IF BIPARJOY FORMS A COMPLETE INNER CORE WITH
CONVECTION ROTATED UPSHEAR (EAST), THIS PEAK INTENSITY COULD BE
HIGHER, BUT IF THE VORTEX BECOMES DECOUPLED DUE TO THE SHEAR, IT
COULD BE LOWER. FORECAST CONFIDENCE REMAINS LOWER THAN AVERAGE.

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

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