Advisories

WDIO31 PGTW 020300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04B (MURASU) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.5N 81.8E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 663 NM SOUTHWEST OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE (TC) 04B (MURASU) WITH A CONSISTENT CENTRAL DENSE OVERCAST
(CDO) WITH COOL CLOUD TOPS MEASURING AT -80 C, OBSCURING THE LOW
LEVEL CIRCULATION CENTER (LLCC). ANIMATED RADAR IMAGERY FROM
CHENNAI REVEALS THE SYSTEM COMING INTO RANGE AS IT APPROACHES THE
EASTERN COAST OF INDIA. ENVIRONMENTAL CONDITIONS ARE ASSESSED AS
FAVORABLE WITH WARM (29-30 C) SEA SURFACE TEMPERATURES (SSTS), LOW
(5-10 KTS) VERTICAL WIND SHEAR (VWS), AND STRONG POLEWARD AND
EQUATORWARD OUTFLOW ALOFT, ALTHOUGH MID-LAYER VWS IS ASSESSED TO BE
CLOSER TO 20 KTS, POSSIBLY INHIBITING FURTHER INTENSIFICATION. THE
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON
SATELLITE IMAGERY. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE AS AGENCY DVORAK FIXES REMAIN CONSISTENT AT 3.5 AND
CIMSS OBJECTIVE ESTIMATES OSCILLATE BETWEEN 55-60 KTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE CENTERED TO THE
NORTHEAST 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   DEMS: T3.5 - 55 KTS
   CIMSS ADT: 57 KTS AT 020000Z
   CIMSS AIDT: 53 KTS AT 012300Z
   CIMSS D-MINT: 62 KTS AT 012357Z
   CIMSS D-PRINT: 56 KTS AT 012330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE INTENSITY AT TAU 24 IS 15 KTS
LOWER THAN PREVIOUSLY FORECAST AS THE SYSTEM HAS NOT INTENSIFIED AS
PREVIOUSLY EXPECTED

FORECAST DISCUSSION: 04B IS EXPECTED TO CONTINUE NORTHWESTWARD
TOWARDS THE EASTERN COAST OF INDIA, WITH LANDFALL EXPECTED BETWEEN
TAUS 12 AND 24. A REASSESSMENT OF THE 1800Z POSITION SHIFTED THE
EXPECTED POINT OF LANDFALL SOUTH BY ROUGHLY 30 NM. TRACK SPEED WILL
SLOW SLIGHTLY AS IT APPROACHES LAND AS A SUBTROPICAL RIDGE (STR)
CENTERED TO THE WEST BUILDS AND WEAKENS THE STEERING GRADIENT
BETWEEN THE PRIMARY STEERING STR CENTERED TO THE NORTHEAST. BETWEEN
TAUS 36 AND 48 A SLIGHT WESTWARD TURN WILL OCCUR AS THE WEAKER
SYSTEM BECOMES PRIMARILY STEERED BY THE SYNOPTIC FLOW. REGARDING
INTENSITY, 04B IS EXPECTED TO MAINTAIN INTENSITY FOR THE NEXT 12
HOURS BEFORE BEGINNING A WEAKENING TREND AS IT MAKES LANDFALL, WITH
TERRAIN INTERACTION QUICKLY CAUSING DISSIPATION OVER LAND BY TAU
48. 

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT FOR THE
REMAINDER OF THE FORECAST PERIOD, WITH THE LARGEST AREA OF
DISAGREEMENT BEING THE TRACK BETWEEN TAUS 36 AND 48 AS MODELS
STRUGGLE TO TRACK THE WEAKENED VORTEX OVER LAND. ALL MODELS EXCEPT
THE OPERATIONAL GOOGLE DEEPMIND AGREE ON A WESTWARD TURN, AT
VARYING TRACK SPEEDS AFTER TAU 36. GFS, NAVGEM, GEFS MEAN, AND THE
EXPERIMENTAL GOOGLE DEEPMIND AND WEATHER MESH MODELS KEEP THE
SYSTEM JUST OFF THE COAST OF INDIA AT TAU 24. THE OFFICIAL JTWC
FORECAST TRACK IS ASSESSED WITH HIGH CONFIDENCE, IN GOOD AGREEMENT
WITH THE MULTI-MODEL CONSENSUS. MODEL INTENSITY GUIDANCE IS ALSO IN
GOOD AGREEMENT, WITH COAMPS-TC AND DECAY-SHIPS BEING THE ONLY
MODELS TO SHOW FURTHER INTENSIFICATION OUT TO TAU 24, AND THEN ALL
MODELS AGREEING OF SHARP WEAKENING THEREAFTER. NOTABLY, THERE WERE
NO RAPID INTENSIFICATION (RI) AIDS THAT TRIGGERED THIS CYCLE. THE
OFFICIAL JTWC FORECAST INTENSITY IS THUS ASSESSED WITH MEDIUM
CONFIDENCE, JUST BELOW THE MULTI-MODEL CONSENSUS OUT TO TAU 24 TO
ACCOUNT FOR UNLIKELY HIGHER PEAKS DEPICTED BY COAMPS-TC AND SHIPS
CAUSING A SPREAD OF 25 KTS AT TAU 24. 

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