Advisories

WDIO31 PGTW 022100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04B (MURASU) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.1N 80.5E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 635 NM SOUTHWEST OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS THE
EXTREMELY COMPACT VORTEX OF TC 04B NEARING LANDFALL ALONG THE
NORTHERN COROMANDEL COAST. TC 04B HAS MAINTAINED A VERY COMPACT
CENTRAL DENSE OVERCAST (CDO), WITH CLOUD-TOP TEMPERATURES COLDER
THAN -80 DEGREES CELSIUS. A 021653Z GMI PASS REVEALED A MICROWAVE
EYE FEATURE WITHIN THE COMPACT VORTEX. THE 021536Z ASCAT-B AND
021241Z RCM-3 SAR PASSES REVEALED EXTREMELY SMALL GALE-FORCE WIND
RADII OF 30-40 NM. BASED ON THE SAR DATA AND ADDITIONAL DVORAK
ANALYSIS, THE 1200Z INTENSITY WAS REANALYZED TO 75 KTS. THE CDO
APPEARS TO HAVE TIGHTENED DURING THE PAST SIX HOURS. RADAR IMAGERY
INDICATES THAT THE PREVIOUSLY OPEN SOUTHWESTERN EYEWALL QUADRANT
HAS CLOSED. THEREFORE, THE INITIAL INTENSITY IS ASSESSED AT AN
UNCERTAIN 85 KTS WITH LOW CONFIDENCE. THIS ASSESSMENT IS HIGHER
THAN THE AVAILABLE SUBJECTIVE AND OBJECTIVE ESTIMATES, WHICH MAY
UNDERESTIMATE THE INTENSITY OF VERY SMALL SYSTEMS. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON A COMBINATION OF
RADAR DATA AND THE EMBEDDED VORTICAL HOT TOWERS. THE ENVIRONMENT IS
MARGINALLY FAVORABLE, WITH SEA SURFACE TEMPERATURES (SST) OF 29-30
DEGREES CELSIUS AND LOW TO MODERATE VERTICAL WIND SHEAR (VWS)
OFFSET BY INCREASING LAND INTERACTION.

INITIAL WIND RADII BASIS: SCATTEROMETER AND SAR DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED NEAR 18N 91E

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   DEMS: T3.5 - 55 KTS
   CIMSS ADT: 59 KTS AT 021800Z
   CIMSS AIDT: 62 KTS AT 021800Z
   CIMSS D-MINT: 62 KTS AT 021712Z
   CIMSS D-PRINT: 69 KTS AT 021800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND WESTWARD
   OTHER FACTORS: LAND INTERACTION

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 04B IS ROUNDING THE SOUTHWESTERN PERIPHERY
OF THE DEEP-LAYER STR. THIS NORTH-NORTHWESTWARD MOTION WILL
CONTINUE THROUGH LANDFALL. THE SYSTEM IS JUST ABOUT OUT OF TIME TO
INTENSIFY FURTHER. WHILE SST REMAINS NEAR 29 DEGREES CELSIUS,
MODERATE VWS AND INCREASING LAND INTERACTION WILL LIMIT FURTHER
DEVELOPMENT. WEAKENING WILL COMMENCE SHORTLY, FOLLOWED BY RAPID
WEAKENING AFTER LANDFALL. AS THE CIRCULATION BECOMES SHALLOW,
LOWER-LEVEL EASTERLY FLOW WILL BECOME THE PRIMARY STEERING
MECHANISM, RESULTING IN A SLIGHT WESTWARD TURN PRIOR TO DISSIPATION
BY TAU 36.

MODEL DISCUSSION: THE TRACK AND INTENSITY GUIDANCE ARE IN GOOD
AGREEMENT. ALL MODELS BRING THE SYSTEM ONSHORE BY TAU 12 AS IT
CONTINUES NORTH-NORTHWESTWARD. THE DYNAMICAL MODELS GENERALLY
DEPICT A SHARPER WESTWARD TURN THAN THE AI-MODELS. THE JTWC
FORECAST TRACK IS PLACED NEAR THE CENTER OF THE GUIDANCE ENVELOPE
THROUGH TAU 36 WITH HIGH CONFIDENCE. THE INTENSITY AIDS UNANIMOUSLY
DEPICT STEADY TO RAPID WEAKENING. JTWC INTENSITY FORECAST IS SET
NEAR THE CORE GROUP OF INTENSITY AIDS, CONSISTING OF HAFS-A, GOOGLE
DEEPMIND, AND COAMPS-TC.

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