WDIO31 PGTW 082100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 02A (BIPARJOY) WARNING 
NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.4N 66.2E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 556 NM SOUTHEAST OF MASIRAH ISLAND
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A RAGGED
CLUMP OF DEEP CONVECTION OBSCURING THE LOW-LEVEL CIRCULATION CENTER
(LLCC) WHICH DOES NOT HAVE MUCH CURVED STRUCTURE. A 081702Z AMSU-B
MICROWAVE PASS SHOWS THAT CONVECTION IS ONLY WRAPPING AROUND THE
SOUTHERN SEMICIRCLE OF THE LLCC, WHICH APPEARS TO BE LOCATED
BENEATH THE EASTERN PART OF THE CONVECTIVE CANOPY BUT IS DIFFICULT
TO IDENTIFY IN AVAILABLE DATA. THE VORTEX STILL APPEARS TO BE
TILTED WESTWARD WITH HEIGHT DUE TO ONGOING MODERATE TO STRONG
EASTERLY VERTICAL SHEAR. THIS IS APPARENT IN THE LACK OF
UPPER-LEVEL OUTFLOW ON THE EASTERN SIDE OF THE CIRCULATION. AND
POLEWARD OUTFLOW IS NOT BEING CHANNELED IN ANY SIGNIFICANT WAY. THE
INITIAL INTENSITY IS SET AT 75 KT BASED ON QUALITY DATA FROM A
081352Z SAR PASS WHICH SHOWED MAXIMUM WINDS OF 76 KT ON THE
SOUTHEASTERN SIDE OF THE LLCC, CONSISTENT WITH SUBJECTIVE DVORAK
ESTIMATES OF T4.5 (77 KT). FORWARD MOTION REMAINS VERY SLOW.

INITIAL WIND RADII BASIS: SAR AND SMOS DATA

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 ADT: 61 KTS AT 081800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 31-32 CELSIUS
   OUTFLOW: MODERATE WESTWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL CYCLONE 02A (BIPARJOY) IS STRUGGLING
MIGHTILY WITH 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 SIGNIFICANTLY (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 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 HAS BEEN SHIFTING EASTWARD, AND EVEN THE GFS ENSEMBLE NOW
HAS A SIGNIFICANT GROUP OF MEMBERS WHICH TRACK INTO PAKISTAN
INSTEAD OF OMAN. 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 MAY NOT BE MOVING AS FAR WEST
AS GFS AND HWRF HAD EXPECTED, AND IF THAT TREND CONTINUES,
CONTINUING SHIFTS EAST IN THE FORECAST MAY BE NEEDED. THE CURRENT
FORECAST IS SHIFTED 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 SHOWS SOME INTENSIFICATION
TO A PEAK OF 90 KT IN 36-48 HOURS, FOLLOWED BY GRADUAL WEAKENING AS
PREDICTED SHEAR VALUES INCREASE EVEN MORE. IF BIPARJOY FORMS A
COMPLETE INNER CORE, THIS PEAK INTENSITY COULD BE HIGHER, BUT IF
THE VORTEX BECOMES DECOUPLED DUE TO THE SHEAR, IT COULD BE LOWER.
THE JTWC FORECAST IS NOT AS STRONG AS GFS OR HWRF, PRIMARILY DUE TO
THEIR INITIALIZATIONS DEPICTING THE VORTEX AS MORE UPRIGHT AND
SYMMETRIC THAN IT CURRENTLY IS IN REALITY, SUGGESTING THAT SHEAR IS
HAVING A GREATER IMPACT THAN THESE TWO MODELS PROJECT. FORECAST
CONFIDENCE IS 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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