Advisories

WDIO31 PGTW 010900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04B (FOUR) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.2N 84.8E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 657 NM SOUTH-SOUTHWEST OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAPIDLY 
CONSOLIDATING, COMPACT SYSTEM CHARACTERIZED BY DEEP CONVECTIVE 
VORTICAL HOT TOWERS WRAPPING UPSHEAR ALONG THE EASTERN FLANK OF THE 
INNER CORE. A 010606Z GMI COLOR-ENHANCED 37GHZ MICROWAVE IMAGE 
REVEALS WELL-DEFINED LOW-LEVEL CONVECTIVE BANDING WRAPPING INTO A 
COMPACT INNER CORE, WHICH EXHIBITS A DISTINCT CYAN RING FEATURE. IN 
THE 89GHZ BAND, THE INNER CORE APPEARS LESS DEVELOPED, DISPLAYING 
PRIMARY BANDING ALONG THE SOUTHERN AND SOUTHEASTERN FLANKS, WHILE THE 
NORTHWESTERN QUADRANT OF THE CIRCULATION REMAINS DEVOID OF DEEP 
CONVECTION. MODEL-DERIVED SOUNDINGS INDICATE THAT WHILE DEEP-LAYER 
VERTICAL WIND SHEAR (VWS) IS LOW, MID-LEVEL SHEAR IS MODERATE OUT OF 
THE NORTH-NORTHWEST, WHICH CORRESPONDS TO THE ASYMMETRIC STRUCTURAL 
APPEARANCE IN THE MICROWAVE IMAGERY. A 010332Z ASCAT-C PASS REVEALED 
AN EXCEPTIONALLY COMPACT INNER CORE WHOSE HORIZONTAL SCALE WAS TOO 
SMALL FOR THE INSTRUMENTS SPATIAL RESOLUTION TO ACCURATELY SAMPLE THE 
MAXIMUM SUSTAINED WINDS, RESOLVING ONLY 30-KT WINDS CONFINED TO 
APPROXIMATELY TWO-THIRDS OF THE LOW-LEVEL CIRCULATION CENTER (LLCC). 
THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE 
37GHZ MICROWAVE IMAGERY. THE INITIAL INTENSITY IS ASSESSED WITH 
MEDIUM CONFIDENCE, BASED ON A BLEND OF THE SUBJECTIVE AND OBJECTIVE 
INTENSITY ESTIMATES OUTLINED BELOW. ENVIRONMENTAL CONDITIONS ARE 
FAVORABLE FOR STEADY TO RAPID INTENSIFICATION (RI), SUPPORTED BY 
ELEVATED SEA SURFACE TEMPERATURES (SSTS), HIGH OCEAN HEAT CONTENT 
(OHC), LOW DEEP-LAYER VWS, AND ROBUST DUAL-CHANNEL OUTFLOW DIRECTED 
EQUATORWARD AND INCREASINGLY POLEWARD. THE PRIMARY INHIBITING FACTOR 
REMAINS THE MODERATE MID-LEVEL SHEAR.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED NEAR COASTAL MYANMAR. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   DEMS: T2.0 - 30 KTS
   CIMSS ADT: 45 KTS AT 010530Z
   CIMSS AIDT: 35 KTS AT 010530Z
   CIMSS D-MINT: 32 KTS AT 010038Z
   CIMSS D-PRINT: 33 KTS AT 010530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST HAS BEEN TRUNCATED TO 60
HOURS WITH DISSIPATION OVER LAND. 

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 04B IS TRACKING WEST-
NORTHWESTWARD AT 16 KTS ALONG THE SOUTHWESTERN PERIPHERY OF THE STR 
POSITIONED TO THE NORTHEAST. AS THE SYSTEM APPROACHES THE COASTLINE 
NEAR TAU 24, BOTH DETERMINISTIC GFS AND ECMWF GUIDANCE FORECAST THE 
STEERING STR TO BIFURCATE INTO TWO DISTINCT ANTICYCLONIC CELLS: A 
PRIMARY CELL OVER THE NORTHERN BAY OF BENGAL AND A SECONDARY CELL 
OVER SOUTHWESTERN INDIA. THIS SYNOPTIC EVOLUTION WILL INDUCE A 
BAROMETRIC COL IN THE RIDGING PATTERN AS THE SYSTEM NEARS THE EASTERN 
COAST OF INDIA. CONSEQUENTLY, TC 04B IS FORECAST TO DECELERATE AFTER 
TAU 24 AS IT ENTERS THIS WEAK STEERING ENVIRONMENT. WHILE THE 
OFFICIAL FORECAST CALLS FOR TC 04B TO PROGRESS SLOWLY INLAND 
FOLLOWING LANDFALL AT TAU 36, DETERMINISTIC FIELDS, PARTICULARLY 
WITHIN THE ECMWF AND TO A LESSER EXTENT THE GFS, INDICATE THE 
POTENTIAL FOR THE SYSTEM TO STALL OFFSHORE FOR APPROXIMATELY 12 
HOURS, DELAYING LANDFALL UNTIL NEAR TAU 48. FOLLOWING LANDFALL, THE 
SYSTEM WILL DRIFT SLOWLY INLAND ALONG THE SOUTHWESTERN PERIPHERY OF 
THE LOW-LEVEL STR AXIS ANCHORED OVER THE BAY OF BENGAL. REGARDING 
INTENSITY, TC 04B IS FORECAST TO INTENSIFY AT A NEAR-RI RATE THROUGH 
TAU 24, REACHING A PEAK INTENSITY OF AT LEAST 65 KTS PRIOR TO 
LANDFALL. SUBSEQUENT TO LANDFALL, TC 04B WILL RAPIDLY WEAKEN DUE TO 
FRICTIONAL DISSIPATION AND TOPOGRAPHIC INTERACTION, LEADING TO 
COMPLETE DISSIPATION OVER EASTERN INDIA BY TAU 60. 

MODEL DISCUSSION: NUMERICAL TRACK GUIDANCE IS IN STRONG AGREEMENT 
THROUGH LANDFALL, WITH ALL CONSENSUS MEMBERS SUPPORTING THE TIMING 
AND LOCATION OF LANDFALL. HOWEVER, AS NOTED ABOVE, SYNOPTIC MODEL 
FIELDS SUGGEST A POTENTIAL 6- TO 12-HOUR OFFSHORE STALL THAT IS 
CURRENTLY OBSCURED WITHIN THE VORTEX TRACKERS DUE TO 12-HOUR TEMPORAL 
SMOOTHING. SHOULD THIS STALL MATERIALIZE, LANDFALL WOULD BE DELAYED 
BY UP TO 12 HOURS, THOUGH THE GEOGRAPHIC LANDFALL LOCATION WOULD 
REMAIN APPROXIMATELY THE SAME. POST-LANDFALL, GUIDANCE REMAINS IN 
GOOD AGREEMENT ON A SLOW INLAND PROGRESSION THROUGH THE REMAINDER OF 
THE FORECAST PERIOD. THE JTWC TRACK FORECAST IS POSITIONED NEAR THE 
GFS AND THE MULTI-MODEL CONSENSUS MEAN WITH MEDIUM CONFIDENCE, WHICH 
IS TEMPERED BY THE TEMPORAL UNCERTAINTY ASSOCIATED WITH THE POTENTIAL 
OFFSHORE STALL. INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE 
SYSTEM WILL INTENSIFY THROUGH TAU 24, THOUGH SIGNIFICANT SPREAD 
EXISTS REGARDING THE MAGNITUDE OF PEAK INTENSITY. HAFS-A AND GOOGLE 
DEEPMIND (GDM) DEPICT A CONSERVATIVE 10 KTS OF ADDITIONAL 
INTENSIFICATION THROUGH LANDFALL. CONVERSELY, CTCX AND HWRF, ALONG 
WITH THE GFS- AND NAVGEM-DRIVEN SHIPS GUIDANCE, ARE NOTABLY MORE 
AGGRESSIVE, INDICATING A PEAK INTENSITY BETWEEN 60 AND 65 KTS. 
MULTIPLE RI AIDS ARE ALSO TRIGGERED, INCLUDING RICN, FRIA, AND RIDE, 
WHICH YIELD PEAK INTENSITIES OF UP TO 75 KTS. THE JTWC INTENSITY 
FORECAST IS ALIGNED CLOSELY WITH THE SHIPS-GFS SOLUTION, 
APPROXIMATELY 5 KTS ABOVE THE HWRF THROUGH LANDFALL, AND SUBSEQUENTLY 
TRACKS NEAR THE HWRF SOLUTION THROUGH THE DISSIPATION PHASE. 

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