Advisories

WDIO31 PGTW 021500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04B (MURASU) WARNING 
NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.7N 80.7E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 645 NM SOUTHWEST OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 27 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A COMPACT 
CENTRAL DENSE OVERCAST (CDO) CHARACTERIZED BY DEEP CONVECTION 
PRODUCING VIGOROUS OVERSHOOTING TOPS IN THE VICINITY OF THE ASSESSED 
LOW-LEVEL CIRCULATION CENTER (LLCC). ANIMATED DOPPLER RADAR 
REFLECTIVITY FROM IMD DEPICTS A WELL-DEFINED RADAR EYE FEATURE 
APPROXIMATELY 15 NM IN DIAMETER, CO-LOCATED BENEATH THE CENTER OF THE 
CDO IN THE EIR IMAGERY. CLOUD-TOP TEMPERATURES WITHIN THE MOST 
VIGOROUS CONVECTIVE UPDRAFTS ARE APPROACHING -90 CELSIUS. IN THE 
UPPER LEVELS, SYNOPTIC-SCALE EASTERLY FLOW OVER THE BAY OF BENGAL 
DIVERGES UPSTREAM OF TROPICAL CYCLONE (TC) 04B, SUPPORTING ROBUST 
DUAL-CHANNEL UPPER-TROPOSPHERIC OUTFLOW THAT IS PARTICULARLY 
PRONOUNCED ALONG THE POLEWARD CHANNEL. THE INITIAL POSITION IS 
ASSESSED WITH HIGH CONFIDENCE BASED ON THE WELL-DEFINED RADAR EYE. 
THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, BASED ON A 
BLEND OF THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES OUTLINED 
BELOW. ENVIRONMENTAL CONDITIONS REMAIN MARGINALLY FAVORABLE OVERALL, 
SUPPORTED BY ELEVATED SEA SURFACE TEMPERATURES (SSTS), STRONG DUAL-
CHANNEL OUTFLOW, AND LOW DEEP-LAYER VERTICAL WIND SHEAR (VWS). 
INHIBITING FACTORS INCLUDE INCREASING OCEANIC UPWELLING INDUCED BY 
THE VORTEX DECELERATING TO 05 KTS OR LESS, MODERATE NORTHWESTERLY 
MID-LEVEL SHEAR, AND CONTINENTAL BOUNDARY-LAYER DRY AIR ENTRAINMENT 
ALONG THE SOUTHWESTERN QUADRANT.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: TROPICAL CYCLONE (TC) 04B IS EMBEDDED
WITHIN A COL REGION BETWEEN SUBTROPICAL RIDGES (STR) OVER THE BAY
OF BENGAL AND SOUTHWESTERN INDIA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   DEMS: T3.5 - 55 KTS
   CIMSS ADT: 59 KTS AT 021130Z
   CIMSS AIDT: 62 KTS AT 021130Z
   CIMSS D-MINT: 66 KTS AT 021002Z
   CIMSS D-PRINT: 67 KTS AT 021130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 0-5 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG POLEWARD AND MODERATE EQUATORWARD
   OTHER FACTORS: PROXIMITY TO LAND, LOCALIZED OCEANIC UPWELLING, AND 
MODERATE MID-LEVEL NORTHWESTERLY SHEAR.  

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST HORIZON HAS BEEN TRUNCATED 
TO 36 HOURS DUE TO FORECAST DISSIPATION OVER LAND. 

FORECAST DISCUSSION: TC 04B HAS CONTINUED TO DECELERATE AS IT 
APPROACHES THE EASTERN INDIAN COASTLINE, EMBEDDED WITHIN A RAPIDLY 
EVOLVING COL REGION BETWEEN TWO ANTICYCLONIC STR CENTERS TO THE 
NORTHEAST AND SOUTHWEST. OVER THE NEXT 12 TO 24 HOURS, THE WESTERN 
STR IS FORECAST TO WEAKEN AND RETROGRADE SOUTHWESTWARD, WHILE THE 
WESTERN PERIPHERY OF THE EASTERN STR WILL REORIENT ALONG A MORE 
MERIDIONAL AXIS, STEERING TC 04B ONTO A NORTH-NORTHWESTWARD 
TRAJECTORY. FORECAST TRANSLATION SPEEDS WILL REMAIN SLOW, HOWEVER, AS 
THE VORTEX SPINS DOWN POST-LANDFALL, VERTICALLY DECOUPLES, AND 
BECOMES GOVERNED BY PROGRESSIVELY LOWER-TROPOSPHERIC STEERING FLOW 
THAT IS WEAKER THAN THE DEEP-LAYER MEAN. LANDFALL IS FORECAST TO 
OCCUR SHORTLY AFTER TAU 12, THOUGH ANY ADDITIONAL DECELERATION OR A 
SHARPER MERIDIONAL DEFLECTION WOULD DELAY LANDFALL BY SEVERAL HOURS 
AND SHIFT THE LANDFALL LOCATION FURTHER POLEWARD ALONG THE COASTLINE. 
FOLLOWING LANDFALL, THE SYSTEM WILL ADVECT SLOWLY INLAND BEFORE 
RECURVING SHARPLY WESTWARD BY THE END OF THE FORECAST PERIOD. 
REGARDING INTENSITY, TC 04B IS UNLIKELY TO INTENSIFY FURTHER PRIOR TO 
LANDFALL AS IT ENTRAINS CONTINENTAL BOUNDARY-LAYER DRY AIR INTO THE 
INNER CORE AND EXPERIENCES DIMINISHED SURFACE HEAT FLUXES NECESSARY 
TO SUSTAIN DEEP, ORGANIZED CONVECTION DUE TO COASTAL OCEANIC 
UPWELLING. SUBSEQUENT TO CROSSING THE COASTLINE, TC 04B WILL RAPIDLY 
SPIN DOWN AND DISSIPATE BY TAU 36 DUE TO SURFACE FRICTIONAL 
DISSIPATION AND TOPOGRAPHIC DISRUPTION. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT, WITH MINIMAL 
CROSS-TRACK DISPERSION THROUGH LANDFALL AND MODESTLY INCREASING 
SPREAD THEREAFTER. THE OFFICIAL JTWC TRACK FORECAST IS PLACED ALONG 
THE EASTERN PERIPHERY OF THE GUIDANCE ENVELOPE, ALIGNED CLOSELY WITH 
THE HAFS-A AND GOOGLE DEEPMIND (GDM) SOLUTIONS, WITH HIGH CONFIDENCE. 
INTENSITY GUIDANCE IS IN STRONG AGREEMENT, WITH ALL GUIDANCE MEMBERS 
SUPPORTING MODEST WEAKENING PRIOR TO LANDFALL FOLLOWED BY RAPID 
INLAND SPIN-DOWN AND DISSIPATION BY TAU 36. THE OFFICIAL JTWC 
INTENSITY FORECAST CLOSELY TRACKS THE MULTI-MODEL INTENSITY CONSENSUS 
(ICNW) THROUGH THE FORECAST PERIOD WITH HIGH CONFIDENCE. 

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