Tropical Storm BANYAN Advisory Mon Oct 31

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (TWENTYSEVEN)
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 7.0N 132.5E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 101 NM WEST OF ANGAUR
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY INDICATES THAT
THE SYSTEM HAS RETAINED A SMALL DEEP CONVECTIVE BURST FIRING OVER
AND OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC). IN THE MIDST
OF STRONG AND PERSISTENT NORTHEASTERLY FLOW ALOFT, THIS CONVECTIVE
BURST HAS ENABLED A SMALL REGION OF RELATIVELY LESS SHEAR ALLOWING
THE SYSTEM TO MAINTAIN A CURRENT INTENSITY OF 35 KTS. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON ANIMATED VISIBLE
IMAGERY, AND THE PGTW FIX POSITION. AN EARLIER 310101Z METOP-C
ASCAT IMAGE SHOWS A COMPACT CIRCULATION WITH 35-40 KTS ON THE
SOUTHERN PERIPHERY. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE PGTW, RJTD, AND KNES DVORAK
INTENSITY ESTIMATES ALONG WITH A COMBINATION OF OBJECTIVE DVORAK
INTENSITY ESTIMATES. THE OVERALL ENVIRONMENT IS MARGINAL, WITH WARM
(30-31C) SEA SURFACE TEMPERATURES (SSTS) AND STRONG EQUATORWARD
OUTFLOW BEING OFFSET BY STRONG NORTHEASTERLY FLOW ALOFT AROUND THE
SYSTEM. HOWEVER, AS MENTIONED ABOVE, THE RELATIVELY LOW VERTICAL
WIND SHEAR (VWS) IN THE VICINITY OF THE LLCC HAS SURPRISINGLY ALLOWED
THE SYSTEM TO HOLD TOGETHER.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTH.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T3.0 - 45 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 35 KTS AT 310230Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: MEDIUM
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: OVER THE PAST SIX HOURS, TROPICAL STORM 27W
HAS GRADUALLY TURNED AND TRACKED TOWARD THE WEST-SOUTHWEST. BY TAU 12
THE SYSTEM IS EXPECTED TO TURN WEST-NORTHWESTWARD INFLUENCED BY THE
STEERING RIDGE TO THE NORTH, WHICH REORIENTS TO A NORTHWEST-SOUTHEAST
DIRECTION. THE SYSTEM WILL THEN CONTINUE ON A NORTHWESTWARD TRACK
THROUGH THE END OF THE FORECAST PERIOD. THE JTWC FORECAST CALLS FOR
THE SYSTEM TO MAINTAIN ITS CURRENT TS STRENGTH OVER THE NEXT 12
HOURS UNDER MARGINAL CONDITIONS. HOWEVER, THE UPPER LEVEL
ENVIRONMENT IS FORECAST TO BECOME LESS FAVORABLE DUE TO UPPER-LEVEL
CONVERGENCE, ALONG WITH MID-LEVEL DRY AIR. THESE UNFAVORABLE
ENVIRONMENTAL CHARACTERISTICS WILL RESULT IN A SLOW WEAKENING TREND
AFTER TAU 24. THE ENVIRONMENTAL CONDITIONS WILL CONTINUE TO DEGRADE
FURTHER WITH DISSIPATION JUST TO THE EAST OF THE SOUTHEASTERN
PHILIPPINES BY TAU 48.
MODEL DISCUSSION: THE NUMERICAL MODEL TRACK GUIDANCE IS IN FAIR
AGREEMENT WITH A GRADUAL SPREAD TO 130NM BY TAU 48, WITH THE
EXCEPTION OF THE COAMPS-TC (CTCI) TRACKER WHICH REPRESENTS THE
SOUTHERN OUTLIER AND THE NAVGEM (NVGI) TRACKER ON THE NORTHERN
PERIPHERY OF THE GUIDANCE ENVELOPE. FOR THIS REASON THE JTWC TRACK
FORECAST TRACK IS PLACED WITH MEDIUM CONFIDENCE AND FOLLOWS CLOSE TO
THE MULTI-MODEL CONSENSUS. THE INTENSITY GUIDANCE IS MIXED WITH DECAY
SHIPS (GFS VERSION) ON THE HIGH END OF THE INTENSITY GUIDANCE, WITH A
PEAK INTENSITY OF 55 KTS. HOWEVER, BOTH GFS AND HWRF REPRESENT THE
LOW END OF THE GUIDANCE WITH A MORE MODEST, 35 KT PEAK INTENSITY.
THEREFORE, THE JTWC FORECAST IS PLACED CLOSER TO THE GFS AND HWRF
INTENSITY SOLUTION AND JUST ABOVE THE MULTI-MODEL CONSENSUS
THROUGHOUT THE FORECAST.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM//
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