Advisories

WDIO31 PGTW 260900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 02B (ARNAB) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.3N 88.4E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 438 NM SOUTH OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE 02B IS RAPIDLY INTENSIFYING. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A 15-NM-WIDE EYE
FORMING WITHIN A RAPIDLY CONSOLIDATING, COMPACT CENTRAL DENSE
OVERCAST (CDO), WITH A LARGE SPIRAL BAND ALONG THE WESTERN
PERIPHERY. A 260333Z ASCAT-B PASS INDICATED THAT THE SYSTEM HAD AT
LEAST ACHIEVED STORM-FORCE INTENSITY AT THAT TIME. SINCE THEN, THE
CONVECTIVE STRUCTURE HAS CONTINUED TO IMPROVE MARKEDLY, WITH A
RAGGED EYE ATTEMPTING TO CLEAR. THE RAPIDLY IMPROVING SATELLITE
PRESENTATION AND RECENT SCATTEROMETER DATA SUGGEST AN APPROXIMATE
30-KT INCREASE IN INTENSITY OVER THE PREVIOUS 12 HOURS. TC 02B IS
TRAVERSING A NEARLY IDEAL ENVIRONMENT, WITH SEA SURFACE
TEMPERATURES (SST) NEAR 30 DEGREES CELSIUS, ABUNDANT DEEP LAYER
MOISTURE, AND LOW VERTICAL WIND SHEAR (VWS). THE INITIAL INTENSITY
IS ASSESSED AT 65 KTS WITH LOW CONFIDENCE, BASED PRIMARILY ON THE
PGTW DVORAK ESTIMATE OF T4.0. THIS ASSESSMENT IS WELL ABOVE THE
AVAILABLE CIMSS OBJECTIVE ESTIMATES, WHICH RANGE FROM 38 TO 45 KTS
AND MAY LAG THE RAPID DEVELOPMENT OF A COMPACT INNER CORE. THE
DVORAK EYE TECHNIQUE YIELDED A DATA T-NUMBER OF 4.5, WHICH SUPPORTS
THE POTENTIAL FOR A HIGHER INTENSITY. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE EYE FEATURE IN MSI.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) POSITIONED OVER SOUTHEAST ASIA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   DEMS: T3.0 - 45 KTS
   CIMSS ADT: 41 KTS AT 260600Z
   CIMSS AIDT: 38 KTS AT 260600Z
   CIMSS D-MINT: 39 KTS AT 260432Z
   CIMSS D-PRINT: 45 KTS AT 260600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE INTENSITY FORECAST HAS BEEN
SIGNIFICANTLY INCREASED.

FORECAST DISCUSSION: TC 02B IS TRACKING WESTWARD ALONG THE SOUTHERN
PERIPHERY OF A DEEP-LAYER STR THAT IS BUILDING WESTWARD. OVER THE
NEXT 24 HOURS, THE RIDGE WILL MAINTAIN A GENERALLY WESTWARD MOTION.
BETWEEN TAU 24 AND TAU 48, INTERACTION WITH A TROPICAL DISTURBANCE
NEAR SRI LANKA MAY INTRODUCE A BRIEF WEST-SOUTHWESTWARD COMPONENT
TO THE TRACK; HOWEVER, WESTWARD MOTION SHOULD REMAIN DOMINANT.
THEREAFTER, TC 02B WILL TURN POLEWARD AS IT REACHES THE WESTERN
PERIPHERY OF THE STR. THE TIMING OF THIS TURN REMAINS A KEY SOURCE
OF TRACK UNCERTAINTY. CONDITIONS WILL REMAIN HIGHLY FAVORABLE FOR
INTENSIFICATION THROUGH TAU 24, WITH SST NEAR 29 30 DEGREES CELSIUS
AND LOW VWS. GIVEN THE ONGOING RAPID INTENSIFICATION, ADDITIONAL
INTENSIFICATION IS EXPECTED THROUGH TAU 24, ALTHOUGH THE RATE OF
INTENSIFICATION REMAINS UNCERTAIN. AFTER TAU 24, A DECREASE IN
FORWARD SPEED MAY INCREASE THE POTENTIAL FOR UPWELLING. IN
ADDITION, VWS IS FORECAST TO INCREASE TO 20-30 KTS, AND LAND
INTERACTION WILL INCREASE AS THE SYSTEM APPROACHES AND MOVES
INLAND. THESE FACTORS ARE EXPECTED TO LEAD TO STEADY TO RAPID
WEAKENING AFTER TAU 24. DISSIPATION OVER LAND WILL OCCUR BY TAU 72.

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH THE
FORECAST PERIOD. GFS AND THE GEFS ENSEMBLE MEAN DIVERGE SLIGHTLY
FROM THE CORE GUIDANCE GROUP BETWEEN TAU 12 AND TAU 36, DEPICTING A
MORE WEST-SOUTHWESTWARD TRACK DUE TO STRONGER INTERACTION WITH THE
TROPICAL DISTURBANCE TO THE SOUTH. THE JTWC FORECAST TRACK IS
PLACED NEAR THE CENTER OF THE TIGHT CORE GUIDANCE CLUSTER,
INCLUDING ECMWF, GOOGLE DEEPMIND, THE MULTI-MODEL CONSENSUS, AND
THE AI-MODEL MEAN. THE CORE GUIDANCE GROUP REMAINS TIGHTLY
CLUSTERED THROUGH TAU 72, ALTHOUGH UNCERTAINTY IN THE DISTURBANCE
INTERACTION AND THE TIMING OF THE POLEWARD TURN SUPPORTS MEDIUM
TRACK CONFIDENCE. INTENSITY GUIDANCE EXHIBITS A LARGE SPREAD.
HAFS-A FORECASTS A PEAK OF 75 KTS, WHILE COAMPS-TC FORECASTS 90 KTS
AND GOOGLE DEEPMIND FORECASTS A PEAK NEAR 115 KTS. GIVEN THE RECENT
RAPID INTENSIFICATION TREND, THE JTWC INTENSITY FORECAST IS PLACED
NEAR THE UPPER END OF THE GUIDANCE ENVELOPE, BUT BELOW THE GOOGLE
DEEPMIND SOLUTION. MOST AVAILABLE INTENSITY GUIDANCE SUPPORTS
WEAKENING AS SHEAR INCREASES AND LAND INTERACTION COMMENCES AFTER
TAU 24, AND THE JTWC FORECAST FOLLOWS THAT OVERALL TREND.

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