WDPN31 PGTW 122100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (MERBOK) WARNING NR 
009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.3N 163.1E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 310 NM NORTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) ALONG WITH WATER VAPOR SATELLITE
IMAGERY SHOWS THE UPPER-LEVEL CONDITIONS ARE FAVORABLE WITH A TUTT
CELL TO THE NORTH OF THE SYSTEM, INCREASING POLEWARD OUTFLOW,
ALLOWING THE SYSTEM TO BECOME BETTER CONSOLIDATED. ADDITIONALLY,
VERTICAL WIND SHEAR IS LOW ALONG WITH WARM SST (29-30C) VALUES
WHICH ARE FAVORABLE FOR FURTHER INTENSIFICATION AND DEVELOPMENT. A
121704Z SSMIS 91GHZ COLOR COMPOSITE MICROWAVE IMAGE REVEALS
CONVECTIVE BANDING WRAPPING INTO A WELL DEFINED LOW-LEVEL
CIRCULATION CENTER. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE 121704Z SSMIS 37GHZ IMAGE AS WELL AS A
CLUSTER OF AGENCY FIXES. THE INITIAL INTENSITY OF 50 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE PGTW DVORAK ESTIMATE
OF T3.0, CIMSS SATCON 54, AND CIMSS ADT 51 KTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NEAR-EQUATORIAL RIDGE (NER) TO THE
SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   CIMSS SATCON: 54 KTS AT 121452Z
   CIMSS ADT: 51 KTS AT 121730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

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: ENVIRONMENTAL CONDITIONS HAVE GRADUALLY
IMPROVE OVER THE PAST 24HRS, AS THE TUTT CELL TO THE NORTH IS
PROVIDING A ROBUST POLEWARD OUTFLOW CHANNEL WHICH WILL AID IN
INTENSIFICATION. TS 15W WILL CONTINUE TRACKING UNDER THE INFLUENCE
OF A NEAR EQUATORIAL RIDGE (NER) IN THE NEAR TERM UNTIL A MORE
POLEWARD TRACK BEGINS AS THE STEERING ENVIRONMENT IS INFLUENCED BY
THE SUBTROPICAL RIDGE TO THE NORTHEAST BY TAU 12. AS VERTICAL WIND
SHEAR CONTINUES TO DECREASE AND STRONG POLEWARD OUTFLOW INCREASES,
TS 15W IS FORECAST TO STEADILY INCREASE IN INTENSITY BY TAU 36. THE
PEAK INTENSITY OF 85 KNOTS IS EXPECTED AROUND TAU 48 OVER WARM SST
(28-29C). HOWEVER, AFTER TAU 48, SST WILL GRADUALLY COOL WITH
EXTRA-TROPICAL TRANSITION (ETT) EXPECTED TO COMMENCE AS THE SYSTEM
BEGINS TO INTERACT WITH THE MIDLATITUDE WESTERLIES AND BAROCLINIC
ZONE. TS 15W WILL COMPLETE ETT BY TAU 72 AS IT GAINS FRONTAL
CHARACTERISTICS AND ACCELERATES NORTHEASTWARD WITHIN THE STRONG
MIDLATITUDE SOUTHWESTERLY FLOW.   


MODEL DISCUSSION: NUMERICAL MODELS ARE IN VERY TIGHT AGREEMENT WITH
A 65NM SPREAD IN SOLUTIONS BY TAU 48. WITH A GRADUAL SPREAD TO
150NM BY TAU 72. ADDITIONALLY, BOTH ECMWF AND GFS ENSEMBLES SHOW
TIGHT AGREEMENT LENDING HIGH CONFIDENCE IN THE JTWC TRACK FORECAST.
THERE IS MEDIUM CONFIDENCE IN THE INTENSITY FORECAST. RELIABLE
INTENSITY GUIDANCE IS IN FAIR AGREEMENT WITH PEAK INTENSITY RANGING
FROM 75 KNOTS TO 90 KNOTS AT TAU 48. HWRF IS IN THE MIDDLE OF
GUIDANCE WITH A PEAK INTENSITY OF 75 KNOTS AT TAU 48. OVERALL
CONFIDENCE IN THE INTENSITY FORECAST IS MEDIUM DUE TO THE EVOLVING
UPPER-LEVEL PATTERN ALONG WITH ENVIRONMENTAL FACTORS HIGHLIGHTED IN
THE FORECAST DISCUSSION.


FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
NNNN