WDPN34 PGTW 132100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 27W (USAGI) WARNING NR 
012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.7N 124.0E
   INITIAL INTENSITY: 130 KTS
   GEOGRAPHIC REFERENCE: 168 NM SOUTHEAST OF APARRI, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 50 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THE SYSTEM
CONTINUED WITH ITS RAPID INTENSIFICATION (RI) AND HAS REACHED SUPER
TYPHOON (STY) CATEGORY, AS EVIDENCED BY A MORE COMPACT COLD CENTRAL
COVER THAT HAS ALMOST COMPLETELY SHED ITS FEEDER BANDS. THE
SHARPLY-OUTLINED EYE HAS REDUCED TO A PINHOLE, 5NM IN DIAMETER, AS THE
CYCLONE APPEARS TO BE UNDERGOING AN EYEWALL REPLACEMENT CYCLE (ERC)
AS INDICATED BY A LARGER EYE FORMING AROUND IT. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE WELL-DEFINED
EYE. THE INITIAL INTENSITY OF 130KTS IS ALSO PLACED WITH HIGH
CONFIDENCE BASED ON IDENTICAL AND TIGHTLY-CLUSTERED DVORAK
INTENSITY ESTIMATES FROM FOUR REPORTING AGENCIES AND REFLECTS THE
6-HR RI. ANALYSIS INDICATES A HIGHLY FAVORABLE ENVIRONMENT WITH
VERY WARM ALONG-TRACK SST IN THE PHILIPPINE SEA, LOW VWS, AND
STRONG RADIAL OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE.

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE TO THE
NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T6.5 - 127 KTS
   KNES: T6.5 - 127 KTS
   DEMS: T6.5 - 127 KTS
   CIMSS SATCON: 110 KTS AT 131630Z
   CIMSS ADT: 97 KTS AT 131800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 05-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: STY USAGI WILL TRACK MORE NORTHWESTWARD AS IT
BEGINS TO ROUND THE WESTERN RIM OF THE STEERING STR AXIS, CLIP THE
NORTHEASTERN TIP OF LUZON JUST EAST OF APARRI AROUND TAU 12, THEN
TRACKS MORE NORTHWARD AFTER TAU 24 AFTER IT ENTERS THE LUZON STRAIT
AND CRESTS THE STR AXIS. A SECONDARY STR BUILDING IN FROM THE WEST
NEAR HAINAN WILL COMPETE FOR STEERING AND SLOW DOWN THE STORM
MOTION, RENDERING THE CYCLONE IN A QUASI-STATIONARY MODE IN THE COL
AREA BETWEEN THE TWO STRS AFTER TAU 48, AT BEST AT A VERY SLOW
NORTHEASTWARD PROGRESSION OFF THE SOUTHEASTERN COAST OF TAIWAN. THE
HIGHLY FAVORABLE ENVIRONMENT WILL MAINTAIN THE CURRENT INTENSITY UP
TO TAU 12; AFTERWARD A GRADUAL WEAKENING IS EXPECTED DUE TO LAND
INTERACTION WITH LUZON AND TAIWAN, COOLER SSTS AND DECREASED OHC
DUE TO UPWELLING IN THE COL, AND INCREASED VWS. BY TAU 120, STY
USAGI WILL BE REDUCED TO 55KTS. THERE IS A DISTINCT POSSIBILITY
THAT THE SYSTEM WILL NOT RECOVER FROM THE ERC AND WEAKEN VS
SUSTAIN THE CURRENT INTENSITY TO TAU 12. THERE IS ALSO A
DISTINCT POSSIBILITY THAT AROUND TAUS 36-48, THE SECONDARY STR WILL
ASSUME STEERING AND DRIVE THE SYSTEM SOUTHWESTWARD TOWARD THE
SOUTH CHINA SEA (BIFURCATION SCENARIO).   

MODEL DISCUSSION: NUMERICAL MODELS ARE IN TIGHT AGREEMENT WITH A
GRADUAL AND EVEN SPREAD TO A MERE 156NM AT TAU 48; HOWEVER, DUE TO
THE POTENTIAL BIFURCATION SCENARIO PROPOSED BY A SMALLER STRAND OF
MODELS INCLUDING NVGM, GFS, AND AEMN, THE MODEL ENVELOPE SPREADS
OUT SIGNIFICANTLY AND DIAMETRICALLY, THERE IS OVERALL MEDIUM
CONFIDENCE IN THE JTWC TRACK FORECAST UP TO TAU 72 AND LOW
CONFIDENCE AFTERWARD. CONSEQUENTLY, THE CONFIDENCES AT BOTH TAUS
ARE THE SAME FOR THE INTENSITY FORECAST.  

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