Advisories

WDPN33 PGTW 072100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (KOGUMA) WARNING NR 
012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.1N 161.6E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 1253 NM EAST-SOUTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED WATER VAPOR IMAGERY INDICATES EXPANDING POLEWARD OUTFLOW
DUE TO DECREASING (10-15 KNOTS) NORTH-NORTHEASTERLY VERTICAL WIND
SHEAR (VWS). CONSEQUENTLY, ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY DEPICTS DEEP CONVECTION BUILDING BACK OVER THE
LOW-LEVEL CIRCULATION, WHICH IS TUCKED UNDER THE NORTHERN EDGE OF
THE CONVECTIVE CORE. MICROWAVE IMAGERY HAS BEEN SPARSE, WITH THE
EXCEPTION OF A 071505Z ATMS 89GHZ MICROWAVE IMAGE, WHICH REVEALS
DEEP CONVECTIVE BANDING OVER THE WESTERN QUADRANT WRAPPING INTO THE
SOUTHERN QUADRANT OF THE LOW-LEVEL CIRCULATION CENTER. DUE TO THE
LOW RESOLUTION OF THE ATMS IMAGE, THERE IS MEDIUM CONFIDENCE IN THE
INITIAL POSITION. BASED ON THE SLIGHTLY IMPROVED STRUCTURE, THE
INITIAL INTENSITY HAS BEEN INCREASED TO 55 KNOTS, WHICH IS
SUPPORTED BY THE SUBJECTIVE DVORAK ESTIMATES RANGING FROM 55-65
KNOTS. THE CIMSS OBJECTIVE ESTIMATES ARE SIGNIFICANTLY LOWER AND
RANGE FROM 38-48 KNOTS. HOWEVER, THE LATEST ADT RAW T NUMBER IS NOW
UP TO 3.4 (ABOUT 55 KNOTS).

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR)
ENTRENCHED TO THE NORTH, WEAKENED SLIGHTLY BY TROPICAL STORM 15E
(NOLO) POSITIONED 630NM TO THE NORTH-NORTHWEST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T4.0 - 65 KTS
   PHFO: T3.5 - 55 KTS
   CIMSS SATCON: 44 KTS AT 071506Z
   CIMSS ADT: 43 KTS AT 071750Z
   CIMSS AIDT: 38 KTS AT 071750Z
   CIMSS D-MINT: 44 KTS AT 071508Z
   CIMSS D-PRINT: 48 KTS AT 071750Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TS 27W IS FORECAST TO TRACK WEST-NORTHWESTWARD
THROUGH TAU 60 ALONG THE SOUTHWEST PERIPHERY OF THE STR, MAINTAINING A 
650-700NM DISTANCE FROM TS 15E (NOLO) THROUGH TAU 60, WHICH IS WITHIN 
THE TYPICAL RANGE FOR WEAK BINARY INTERACTION. VWS IS FORECAST TO 
CONTINUE TO LESSEN, WHICH WILL ALLOW TS 27W TO RAPIDLY INTENSIFY TO 
120 KNOTS BY TAU 60. AFTER TAU 60, TS 27W WILL TURN NORTHWESTWARD TO 
NORTH-NORTHWESTWARD WHILE SLOWING TO ABOUT 7 KNOTS AS IT ROUNDS THE 
WESTERN PERIPHERY OF THE STR. AFTER TAU 72, THE SYSTEM WILL GRADUALLY 
WEAKEN DUE TO INCREASING VWS OF 20-25 KNOTS AND DRY AIR ENTRAINMENT 
OVER THE SOUTHERN PERIPHERY.  

MODEL DISCUSSION: THE PHYSICS-BASED MODELS ARE IN FAIR AGREEMENT
THROUGH TAU 72, WITH A 150NM SPREAD IN THE GUIDANCE, DIVERGING
AFTER TAU 72 DUE TO UNCERTAINTY IN THE RECURVE TRACK AND SOME
POTENTIAL FOR WEAK BINARY INTERACTION AS INDICATED BY ECMWF NEAR
TAU 72. THE JTWC FORECAST IS POSITIONED CLOSE TO AICN AND CONW
THROUGH TAU 96 THEN SOUTHWEST OF CONW, CLOSER TO AICN AT TAU 120 TO
OFFSET EEMI AND ECMI, WHICH ARE RECURVING THE SYSTEM RAPIDLY
NORTHEASTWARD. THE BULK OF THE ECMWF ENSEMBLE (ECENS) SOLUTIONS
SUPPORT THE JTWC TRACK SCENARIO, WITH A FEW MEMBERS INDICATING A
SLOW OR QUASI-STATIONARY TRACK MOTION DUE TO BINARY INTERACTION IN
THE EXTENDED FORECAST PERIOD. GOOGLE DEEP MIND IS SIMILAR TO ECENS,
WITH THE LARGE MAJORITY OF SOLUTIONS SUPPORTING THE JTWC TRACK
FORECAST. THERE IS SUBSTANTIAL SUPPORT FOR RAPID INTENSIFICATION
(RI), WITH THE COAMPS-TC (GFS) INDICATING 100 PERCENT PROBABILITY
OF RI FROM TAU 12 TO TAU 48. ADDITIONALLY, RI AIDS HAVE
CONSISTENTLY TRIGGERED SUPPORTING THE IMMINENT RI PHASE.          

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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