WDPN31 PGTW 030300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (NYATOH) WARNING NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.9N 138.7E
   INITIAL INTENSITY: 125 KTS
   GEOGRAPHIC REFERENCE: 275 NM SOUTH-SOUTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 18 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TY 27W HAS MAINTAINED ITS INTENSITY OVER THE PAST SIX HOURS, THOUGH
IT IS BEGINNING TO EXHIBIT SIGNS OF ITS IMPENDING DEMISE. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THAT THE CONVECTIVE
CORE HAS ERODED SIGNIFICANTLY OVER THE PAST SIX HOURS, WITH CLOUD
TOPS WARMING ABOUT 8C, AND THE EXTENT OF THE COLD CONVECTIVE
SHRINKING DRAMATICALLY, ESPECIALLY IN IMAGERY AFTER THE 0000Z HOUR.
ADDITIONALLY, THE CONTINUED ENCROACHMENT OF DRY AIR AND HIGH
WESTERLY SHEAR ARE STARTING TO ERODE THE WESTERN SIDE OF THE
CONVECTIVE CORE. WHILE THE STRUCTURE IS MANIFESTLY DETERIORATING,
THE OBJECTIVE AND SUBJECTIVE DVORAK CURRENT INTENSITY ESTIMATES
REMAIN HIGH, AT OR ABOVE 125 KNOTS. ADDITIONALLY, A 022117Z SMAP
PASS SHOWED 115 KNOT MEASUREMENTS IN THE SOUTHWESTERN PORTION OF
THE EYEWALL, WHICH WHEN APPLYING THE .93 CONVERSION FACTOR RESULTS
IN A 124 KNOT 1-MIN WIND ESTIMATE. THESE FACTORS COMBINE TO LEND
HIGH CONFIDENCE TO THE INITIAL INTENSITY. THE INITIAL POSITION IS
BASED ON THE CONGRUENCE OF AGENCY FIX POSITIONS WITHIN THE 30-NM
RAGGED EYE FEATURE WITH HIGH CONFIDENCE. THE OVERALL ENVIRONMENT IS
BECOMING INCREASINGLY UNFAVORABLE WITH INCREASING MID-LEVEL DRYNESS
DARTING DIRECTLY INTO THE LOW LEVEL VORTEX. ADDITIONALLY, THE HIGH
(40-45 KNOTS) WEST-SOUTHWESTERLY WIND SHEAR IS STARTING TO DOMINATE
THE ROBUST POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T6.5 - 127 KTS
   KNES: T6.5 - 127 KTS
   CIMSS SATCON: 135 KTS AT 022217Z
   CIMSS ADT: 137 KTS AT 022340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 30+ KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TY 27W HAS SOMEWHAT SURPRISINGLY HELD FIRM IN
THE FACE OF RAPIDLY DETERIORATING ENVIRONMENTAL CONDITIONS. PER
HWRF AND GFS MODEL CROSS-SECTIONS AND SKEW-T ANALYSIS, MID-LEVEL
DRY AIR IS POURING INTO THE CORE FROM THE WEST, AND SHEAR ESTIMATES
ARE NOW APPROACHING 45-50 KNOTS. CIMSS ANALYSIS CONFIRMS THE HIGH
SHEAR ESTIMATES. YET THE SYSTEM HAS TO DATE FOUGHT OFF THESE
INHIBITING FACTORS, AND WHILE THE EYE HAS WIDENED AND BECOME MORE
RAGGED, IT IS STILL GOING STRONG. HOWEVER, THE LIGHT ON THE FREIGHT
TRAIN IS GETTING LARGER AND THE HEADY DAYS OF BEING A NEAR-SUPER
TYPHOON STRENGTH SYSTEM WILL SOON COME TO AN END. THE SYSTEM IS
FORECAST TO CONTINUE TRACKING NORTHEAST WHILE STEADILY SLOWING
THROUGH TAU 36. IT IS EXPECTED THAT THE STEADILY INCREASING SHEAR
AND DRY AIR ENTRAINMENT WILL ERODE THE EYE AND BEGIN TO DECAPITATE
THE SYSTEM WITHIN THE NEXT 12 TO 24 HOURS, AND ONCE THIS OCCURS,
RAPID WEAKENING WILL ENSUE. THE SYSTEM IS FORECAST TO BECOME FULLY
DECOUPLED BY TAU 36, AND THUS THE STEERING LEVEL WILL LOWER
PRECIPITOUSLY, DOWN TO THE 850MB LEVEL. THE SURFACE-850MB MEAN FLOW
IN THE AREA IS FROM THE NORTH-NORTHEAST, AND THIS FLOW WILL PUSH
THE RAPIDLY WEAKENING TY 27W ONTO A SOUTHWESTWARD TRACK BY TAU 48.
THE SYSTEM IS EXPECTED TO FULLY DISSIPATE TO A REMNANT LOW LEVEL
CIRCULATION BY TAU 72. 

MODEL DISCUSSION: TRACK GUIDANCE UNCERTAINTY HAS INCREASED SINCE
THE PREVIOUS RUN. WITH THIS RUN, THE GFS, GFS ENSEMBLE, UKMET
ENSEMBLE AND HWRF CONTINUE TO SHOW THE DISSIPATING SYSTEM TURNING
SHARPLY SOUTHWARD AFTER TAU 36. WITH THIS RUN HOWEVER, THE NAVGEM,
ECMWF, ECMWF ENSEMBLE AND GALWEM BLOW RIGHT THROUGH THE TURN AND
CONTINUE RACING THE VORTEX TO THE NORTHEAST, LEADING TO SIGNIFICANT
MODEL SPREAD AND UNCERTAINTY. THE JTWC FORECAST REMAINS CONSISTENT
WITH THE PREVIOUS FORECASTS AND CLOSELY TRACKS THE GFS THROUGH TAU
48, THOUGH IS MUCH SLOWER THROUGH TAU 72. DUE TO THE UNCERTAINTY
INTRODUCED IN THIS RUN OF THE GUIDANCE, THERE IS NOW LOW CONFIDENCE
IN THE FORECAST. CONVERSELY, INTENSITY GUIDANCE IS IN GOOD
AGREEMENT ON A RAPID AND STEADY WEAKENING THROUGH THE FORECAST
PERIOD WITH DISSIPATION NO LATER THAN TAU 72, LENDING MEDIUM
CONFIDENCE TO THE FORECAST.  

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM//
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