Tropical Storm BANYAN Advisory vie, 31-12

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (NYATOH) WARNING NR
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 13.2N 137.0E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 231 NM NORTH-NORTHWEST OF YAP
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED WATER VAPOR IMAGERY AND ENHANCED INFRARED (EIR) SATELLITE
IMAGERY VERIFY CONTINUING CONSOLIDATION AND COOLING CLOUD TOPS
AROUND THE LOW LEVEL CIRCULATION CENTER (LLCC). DEEP CONVECTION HAS
BECOME ESTABLISHED OVER THE ENTIRE EASTERN SEMICIRCLE AND IS
INTENSIFYING. THE CURRENT INTENSITY ASSESSMENT RAISES THE JTWC
DVORAK
ASSESSMENT OF T3.0 (45KTS) BASED ON HIGHER AUTOMATED ASSESSMENTS
OF 50KTS FROM BOTH SATCON AND ADT. TROPICAL STORM NYATOH IS ROUNDING
THE SUBTROPICAL RIDGE AND ENTERING THE LEG OF ITS JOURNEY THAT IT IS
EXPECTED TO INTENSITY SUBSTANTIALLY AS IT GETS AN OUTFLOW BOOST
WHILE REMAINING IN AN AREA OF LOW WIND SHEAR AND HIGH OCEAN HEAT
CONTENT. WATER VAPOR ANIMATION VERIFIES THAT TS NYATOH IS NOT ONLY
TAPPING INTO A POLAR OUTFLOW CHANNEL, BUT HAS DEVELOPED SUBSTANTIAL
EQUATORWARD OUTFLOW. IT IS NOT A TEXTBOOK CASE OF DUAL CHANNEL
OUTFLOW,
BUT THE OVERALL ENVIRONMENT IS VERY RIPE FOR INTENSIFICATION.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: THE FAR WESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE TO THE NORTHWEST.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 50 KTS AT 301740Z
   CIMSS ADT: 51 KTS AT 301740Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: TROPICAL STORM 27W IS BEGINNING THE PERIOD
IN WHICH IT WILL ROUND THE AXIS OF THE SUBTROPICAL RIDGE AND
INTENSIFY DUE TO ENHANCED OUTFLOW AND SUSTAINED LOW VERTICAL
WINDSHEAR AND HIGH OCEAN HEAT CONTENT. A DEEP STORM SYSTEM MOVING
OFF THE CONTINENT IS SUPPORTED BY A DEEP LONG TROUGH THAT WILL
ENHANCE POLEWARD OUTFLOW AND DRAW THE SYSTEM POLEWARD. DRY AIR
BEHIND ITS ASSOCIATED COLD FRONT WILL BEGIN WRAPPING INTO THE
CORE OF THE CIRCULATION NEAR 02/18Z AND WILL BE CHOKING OFF THE
SYSTEM BY 03/00Z. CONCURRENTLY, THE TROUGH WILL BEGIN WORKING
AGAINST
THE STORM NEAR 02/18Z AS ITS ASSOCIATED VERTICAL WINDSHEAR STEADILY
INCREASES TO AN UNTENABLE 35KTS BY 03/00Z. DURING THE TAU 96
THROUGH TAU 120, DECOUPLING OF THE LOW LEVEL VORTEX FROM THE
MAIN BODY OF THE STORMS ENERGY WILL COMPLETE AND LEAVE BEHIND
A SUBSTANTIALLY WEAKEND VORTEX DRFITING UNDER THE NEW EXTENSION
OF THE SUBTROPICAL RIDGE THAT HAS BUILT SEAWARD FROM THE CONTINENT.
MODEL DISCUSSION: DURING THE PAST 48 HOURS MODEL GUIDANCE HAS
TIGHTENED UP SUBSTANTIALLY REGARDING THE DECOUPLING SCENARIO.
CONFIDENCE IN THE LOCATION AND INTENSITY OF THE LEFTOVER VORTEX
REMAINS VERY LOW, BUT THE CERTAINTY REGARDING A SURGE IN INTENSITY
OVER THE NEXT 36 TO 48 HOUR HAS ALSO INCREASED. THE TRACK FORECAST
LIES CLOSE TO THE MULTI MODEL CONSENSUS WHILE THE INTENSITY
FORECAST RUNS ON THE HIGH END OF THE GUIDANCE DUE TO AN OBSERVED
TREND OF THE GUIDANCE UNDERESTIMATING THE NEARLY IDEAL ENVIRONMENTAL
CONDITIONS THE STORM IS TRACKING THROUGH.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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