Advisories

WDIO31 PGTW 270900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 02B (ARNAB) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.2N 83.8E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 464 NM SOUTHWEST OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 38 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAPIDLY
INTENSIFYING, COMPACT TROPICAL CYCLONE WITH SYMMETRIC, RAPIDLY 
COOLING CLOUD TOPS AND A CLEAR, PINHOLE EYE. ANIMATED RADAR DATA
FROM THE INDIA METEOROLOGICAL DEPARTMENT (IMD) DEPICTS A 10-NM WIDE 
RADAR EYE FEATURE SURROUNDED BY VIGOROUS CONVECTIVE BANDING ALONG THE 
WESTERN SEMICIRCLE. A 270333Z ASCAT-C PASS REVEALED A COMPACT INNER 
CORE OF EXTREME WINDS WITH A WELL-DEFINED CENTER. WIND RADII HAVE 
BEEN UPDATED TO REFLECT THE WIND FIELD OBSERVED IN THE ASCAT DATA. IN 
THE UPPER LEVELS, THE SYSTEM HAS DEVELOPED A STRONG MESOSCALE 
ANTICYCLONE POSITIONED DIRECTLY OVER THE LLCC, WHILE SYNOPTIC 
SOUTHERLY FLOW PROVIDES A ROBUST POLEWARD OUTFLOW CHANNEL. THE 
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON CONCURRENT 
RADAR AND MSI EYE FIXES. THE INITIAL INTENSITY IS ASSESSED WITH 
MEDIUM CONFIDENCE, BASED ON A BLEND OF OBJECTIVE INTENSITY ESTIMATES 
NOTED BELOW, AS SUBJECTIVE DVORAK CURRENT INTENSITY (CI) ESTIMATES 
ARE LIKELY UNDERESTIMATING INTENSITY DUE TO THE PINHOLE EYE. 
ENVIRONMENTAL CONDITIONS ARE HIGHLY FAVORABLE FOR ADDITIONAL
INTENSIFICATION PRIOR TO LANDFALL, CHARACTERIZED BY WARM SEA SURFACE 
TEMPERATURES (SSTS), HIGH OCEANIC HEAT CONTENT (OHC), ROBUST
POLEWARD OUTFLOW, AND LOW-TO-MODERATE VERTICAL WIND SHEAR (VWS).

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) OVER EXTREME SOUTHERN CHINA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   DEMS: T4.5 - 77 KTS
   CIMSS ADT: 115 KTS AT 270530Z
   CIMSS AIDT: 114 KTS AT 270530Z
   CIMSS D-MINT: 109 KTS AT 270411Z
   CIMSS D-PRINT: 129 KTS AT 270530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   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 (TC) 02B IS MOVING WESTWARD
ALONG THE SOUTHWESTERN FLANK OF AN EXPANSIVE STR CENTERED OVER
EXTREME SOUTHERN CHINA. TC 02B HAS BEEN DECELERATING OVER THE PAST 12
HOURS AS IT APPROACHES THE COASTLINE, PRIMARILY DUE TO TWO FACTORS;
FIRST, THE STR IS PROGRESSING SLOWLY EASTWARD, RELAXING THE LOCAL 
STEERING GRADIENT, AND SECOND, THE PRESENCE OF A NEW AREA OF CYCLONIC
ROTATION, DESIGNATED INVEST 90B, LOCATED APPROXIMATELY 300 NM TO
THE SOUTHEAST, WITH WHICH 02B IS UNDERGOING BINARY INTERACTION. OVER 
THE NEXT 12 TO 36 HOURS, TC 02B IS FORECAST TO CONTINUE DECELERATING 
AS 90B TRACKS RAPIDLY NORTHEASTWARD, THEN NORTHWARD AT A 250-300 NM 
RANGE FROM THE CENTER OF 02B. THIS CYCLONIC VORTEX ADVECTION WILL 
IMPART A DEFLECTIVE PULL ON TC 02B, SLOWING FORWARD TRANSLATION AS IT
APPROACHES THE COAST. SOME NUMERICAL MODELS, SPECIFICALLY THE ECMWF,
SHOW TC 02B STALLING OFF THE COAST FOR 24 HOURS AS 90B PROPAGATES
NORTH OF 02B PRIOR TO LANDFALL. THE GFS, CONVERSELY, DEPICTS TC 02B 
MAKING LANDFALL FIRST, THEN STALLING OVER THE GODAVARI RIVER DELTA 
REGION BEFORE TURNING NORTHWARD. BOTH SOLUTIONS INDICATE THE PRIMARY 
DRIVER OF NEAR-TERM MOTION IS BINARY INTERACTION WITH 90B. BY TAU 36, 
THE SYSTEM WILL REORIENT NORTHWARD, TRACKING INLAND OVER EASTERN
INDIA. REGARDING INTENSITY, TC 02B HAS RAPIDLY INTENSIFIED UNDER 
HIGHLY CONDUCIVE ENVIRONMENTAL CONDITIONS OVER THE PAST 24 HOURS. 
CONDITIONS REMAIN FAVORABLE, AND TC 02B IS FORECAST TO INTENSIFY 
FURTHER PRIOR TO LANDFALL. OWING TO WARM SHELF WATERS, TC 02B MAY 
REACH A PEAK INTENSITY BETWEEN 120 AND 130 KTS PRIOR TO LANDFALL. THE 
SYSTEM IS FORECAST TO MAKE LANDFALL OVER THE EXTENSIVE RIVER
DELTA REGION, WHERE THE BROWN OCEAN EFFECT WILL MODERATE THE PACE OF 
WEAKENING THROUGH TAU 24. AFTER THE SYSTEM CLEARS THE DELTA REGION, 
IT WILL RAPIDLY WEAKEN, DISSIPATING AS A TROPICAL CYCLONE NO LATER 
THAN TAU 60 DUE TO RUGGED TOPOGRAPHY AND FRICTIONAL DECAY.  

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT OVERALL, WITH
ALL CONSENSUS MEMBERS SUPPORTING A WESTWARD TRACK THROUGH LANDFALL,
A SLOW MEANDERING PERIOD NEAR THE GODAVARI DELTA, THEN A POLEWARD 
TURN. NAVGEM IS A SIGNIFICANT OUTLIER, SHOWING THE SYSTEM REMAINING
OFFSHORE OF THE DELTA REGION AND MAKING LANDFALL AFTER TAU 24 NEAR
VISAKHAPATNAM, INDIA. THE UNCERTAINTY SURROUNDING THE BINARY
INTERACTION IS EVIDENT PRIMARILY IN RAW PROGNOSTIC MODEL FIELDS; 
MODEL TRACKERS SMOOTH THIS DEFLECTION, SHOWING ONLY MODEST 
DECELERATION IN FORWARD SPEED THROUGH LANDFALL. THE JTWC TRACK 
FORECAST IS PLACED NEAR THE MULTI-MODEL CONSENSUS MEAN, ADJUSTED 
SLIGHTLY SLOWER IN THE NEAR TERM TO ACCOUNT FOR BINARY INTERACTION 
WITH 90B, WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD 
AGREEMENT. THE JTWC INTENSITY FORECAST IS PLACED NEAR HAFS-A ON THE 
HIGHER EDGE OF THE GUIDANCE ENVELOPE TO ACCOUNT FOR THE BROWN-OCEAN 
EFFECT IN THE NEAR TERM WITH MEDIUM CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: MEDIUM//
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