Advisories

WDIO31 PGTW 011500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04B (MURASU) WARNING 
NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.8N 83.8E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 644 NM SOUTH-SOUTHWEST OF KOLKATA, INDIA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A RAPIDLY 
DEVELOPING TROPICAL CYCLONE (TC) FEATURING A HIGHLY COMPACT CENTRAL 
DENSE OVERCAST (CDO) WITH EXTREMELY COLD CLOUD TOPS COOLER THAN -85 
CELSIUS WITHIN THE DEEPEST CONVECTIVE UPDRAFTS. A 011147Z SSMIS 89GHZ 
MICROWAVE IMAGE REVEALED FORMATIVE CONVECTIVE BANDING FEATURES ACROSS 
THE SOUTHERN SEMICIRCLE OF THE SYSTEM, WRAPPING INTO THE COMPACT LOW-
LEVEL CIRCULATION CENTER (LLCC). MODERATE NORTHWESTERLY MID-LEVEL 
VERTICAL WIND SHEAR (VWS) IS EVIDENT IN THE MICROWAVE IMAGERY AS A 
SLOT OF RELATIVELY DRY, CONVECTION-FREE AIR INTRUDING ALONG THE 
WESTERN FLANK OF THE INNER CORE. IN THE UPPER LEVELS, ATMOSPHERIC 
MOTION VECTORS (AMVS) DEPICT A DIVERGENT SPLIT-FLOW REGIME UPSTREAM 
OF TC 04B, SUPPORTING ROBUST POLEWARD AND EQUATORWARD OUTFLOW 
CHANNELS. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE 
BASED ON A NASCENT WARM SPOT IN THE EIR IMAGERY AND THE MICROWAVE 
IMAGERY NOTED ABOVE. 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 ADDITIONAL INTENSIFICATION, AND POTENTIALLY RAPID 
INTENSIFICATION (RI), CHARACTERIZED BY ELEVATED (30-31 CELSIUS) SEA 
SURFACE TEMPERATURES (SSTS), HIGH OCEAN HEAT CONTENT (OHC), LOW DEEP-
LAYER VWS, AND STRONG DUAL-CHANNEL OUTFLOW ALOFT, TEMPERED SLIGHTLY 
BY THE PERSISTENT NORTHWESTERLY MID-LEVEL SHEAR.

INITIAL WIND RADII BASIS: PERSISTENCE AND OBJECTIVE BEST TRACK 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   CIMSS ADT: 55 KTS AT 011130Z
   CIMSS AIDT: 43 KTS AT 011100Z
   CIMSS D-MINT: 45 KTS AT 011147Z
   CIMSS D-PRINT: 50 KTS AT 011130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD
   OTHER FACTORS: MODERATE NORTHWESTERLY MID-LEVEL SHEAR. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 04B CONTINUES TO TRACK WEST-NORTHWESTWARD 
ALONG THE SOUTHWESTERN PERIPHERY OF THE STR ANCHORED TO THE NORTHEAST 
NEAR MYANMAR. OVER THE NEXT 12 TO 24 HOURS, DETERMINISTIC GLOBAL 
MODELS CONCUR THAT THE WESTERN EXTENSION OF THE RIDGE POSITIONED TO 
THE NORTH OF TC 04B WILL WEAKEN AND BIFURCATE INTO TWO DISTINCT 
ANTICYCLONIC CENTERS. THIS EVOLUTION WILL INDUCE A COL IN THE 
SYNOPTIC STEERING PATTERN ALONG THE EASTERN COAST OF INDIA. AS TC 04B 
ENTERS THIS COL REGION, IT WILL DECELERATE UPON APPROACHING THE 
COASTLINE. THE ONSET OF THIS RIDGE BREAKDOWN HAS BEEN DELAYED BY 
APPROXIMATELY 6-12 HOURS RELATIVE TO PREVIOUS MODEL CYCLES; 
CONSEQUENTLY, WHILE TC 04B WILL DECELERATE AS IT APPROACHES THE 
COASTLINE, NEITHER THE GFS NOR THE ECMWF CURRENTLY DEPICTS AN 
OFFSHORE STALL. TC 04B IS FORECAST TO MAKE LANDFALL AT TAU 36 BEFORE 
PROGRESSING SLOWLY INLAND, INITIALLY TRACKING NORTHWARD AND 
SUBSEQUENTLY RECURVING NORTHWESTWARD AS THE SHALLOWING VORTEX BECOMES 
GOVERNED BY PROGRESSIVELY LOWER-TROPOSPHERIC STEERING FLOW. REGARDING 
INTENSITY, THE SYSTEM IS EMBEDDED IN A FAVORABLE TO HIGHLY FAVORABLE 
THERMODYNAMIC AND DYNAMIC ENVIRONMENT CONDUCIVE TO POTENTIAL RI. THE 
PRIMARY INHIBITING FACTOR IS THE FORECAST PERSISTENCE OF ENHANCED 
MID-LEVEL NORTHWESTERLY SHEAR. HOWEVER, THE CIRCULATION IS EXPECTED 
TO REMAIN HIGHLY COMPACT, WHICH PROMOTES HIGHER INERTIAL STABILITY 
AGAINST MID-LEVEL SHEAR WHILE SIMULTANEOUSLY RENDERING THE VORTEX 
SUSCEPTIBLE TO RAPID INTENSITY FLUCTUATIONS. THE OFFICIAL FORECAST 
CALLS FOR A NEAR-RI RATE OF INTENSIFICATION THROUGH LANDFALL, THOUGH 
A HIGHER PEAK INTENSITY OCCURRING IMMEDIATELY PRIOR TO LANDFALL, 
BETWEEN STANDARD SYNOPTIC FORECAST TAUS, REMAINS A DISTINCT 
POSSIBILITY. FOLLOWING LANDFALL, THE SYSTEM WILL RAPIDLY WEAKEN DUE 
TO FRICTIONAL DISSIPATION AND TOPOGRAPHIC DISRUPTION, DISSIPATING BY 
TAU 60.  

MODEL DISCUSSION: TRACK GUIDANCE IS IN STRONG AGREEMENT THROUGH THE 
FORECAST PERIOD, WITH MINIMAL CROSS-TRACK SPREAD OF ONLY 45 NM AT 
LANDFALL. AS NOTED ABOVE, WHILE THE GFS DEPICTS A SLIGHT 
NORTHWESTWARD DEFLECTION BY TAU 36, SHIFTING THE LANDFALL LOCATION 
NORTH OF THE CONSENSUS MEAN, NO GUIDANCE MEMBERS CURRENTLY INDICATE A 
COASTAL STALL. THE JTWC TRACK FORECAST IS PLACED NEAR THE MULTI-MODEL 
CONSENSUS MEAN THROUGH TAU 24, THEN SHIFTS TO THE NORTHERN BOUNDARY 
OF THE GUIDANCE ENVELOPE, ALIGNED CLOSELY WITH THE GFS, THROUGH THE 
REMAINDER OF THE FORECAST PERIOD. INTENSITY GUIDANCE IS BIFURCATED, 
WITH THE OPERATIONAL AND EXPERIMENTAL GOOGLE DEEPMIND (GDM) MODELS 
AND HAFS-A DEPICTING MINIMAL ADDITIONAL INTENSIFICATION PRIOR TO 
LANDFALL (WITH HAFS-A PEAKING WITHIN 5 KTS OF THE HWRF). CONVERSELY, 
THE CTCX, SHIPS, AND THE INTENSITY CONSENSUS (ICNW) ARE SIGNIFICANTLY 
MORE AGGRESSIVE, INDICATING A PEAK INTENSITY OF 70-75 KTS. MULTIPLE 
PROBABILISTIC RI AIDS (RIPA, RIDE, RICN, FRIA, AND RI30-RI60) ARE 
ALSO TRIGGERED, INDICATING POTENTIAL PEAK INTENSITIES AS HIGH AS 90 
KTS. THE JTWC INTENSITY FORECAST IS ALIGNED WITH THE CTCX SOLUTION 
THROUGH THE FORECAST PERIOD. 

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