WDPN31 PGTW 292100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (TWENTYSEVEN) 
WARNING 
NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.6N 140.3E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 256 NM WEST OF NAVSTA GUAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
DEEPENING CONVECTION CONSOLIDATING OVER THE LOW LEVEL CIRCULATION
CENTER (LLCC). THE INITIAL POSITION LIES IN THE CENTER OF A TIGHT
CLUSTER OF FIXES FROM JTWC, RJTD, AND KNES. A WELL-TIMED AMSR2 PASS
AT 291635Z REVEALS A CLEAR CENTER ON THE 37H AND 37V BANDS AND ALSO
SHOWS THAT DEEP CONVECTION IS NOW NEARLY CONTINUOUS AROUND THE CORE.
THE INITIAL INTENSITY ASSESSMENT IS BASED ON A RAW ADJ T VALUE OF
2.6 FROM ADT AND THE CI HAS INCREASED TO T2.3 (33KTS). THE JTWC
DVORAK ALSO INCREASED OVER THE PAST SIX HOURS. ANIMATED WATER VAPOR
IMAGERY ALSO SHOWS EXCELLENT OUTFLOW WITH THE SYSTEM INCLUDING A
DEVELOPING POLEWARD OUTFLOW CHANNEL. IN ADDITION TO THE FAVORABLE
OUTFLOW CONDITIONS, TS 27W IS TRACKING THROUGH A REGION OF LOW
VERTICAL WINDSHEAR (VWS) AND HIGH OCEAN HEAT CONTENT.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: THE DEEP LAYERED SUBTROPICAL RIDGE TO
THE NORTHWEST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 33 KTS AT 291740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: THERE IS ALSO MODERATELY STRONG EQUATORWARD
OUTFLOW.

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 27W WILL CONTINUE ALONG A NORTHWESTERLY 
BEARING UNTIL IT ROUNDS THE STR RIDGE AXIS NEAR THE 16TH LATITUDE, 
THEN ROLL OVER TO THE NORTHWEST IN RESPONSE TO HEIGHT FALLS 
ASSOCIATED WITH A VERY DEEP AND VIGOROUS COLD FRONT THAT IS NOW 
APPROACHING THE KOREAN PENINSULA. AS IT ROUNDS THE RIDGE A FULLY 
DEVELOPED POLEWARD OUTFLOW CHANNEL WILL CAUSE A SHARP INCREASE IN 
INTENSITY. TS 27W WILL PEAK IN INTENSITY BETWEEN THE 18TH AND 20TH
LATITUDES, THEN AN INFLUX OF COOLER AND DRIER AIR ASSOCIATED WITH
THE WPAC COLD SURGE WILL COUPLE WITH INCREASING VWS TO INITIATE AN
INTENSITY DOWNTREND. DURING THE 96-120 HOUR PERIOD, THE DEEP TROUGH
IS EXPECTED TO PASS POLEWARD OF THE STORM AND NOT QUITE PICK IT UP,
WHEREUPON THE SUBTROPICAL RIDGE WILL BUILD BACK IN AND DRIVE THE
SYSTEM WESTWARD. THAT ROLLOVER WILL OCCUR DURING AND JUST AFTER
THE FURTHEST TAUS OF THIS FORECAST. 

MODEL DISCUSSION: TRACK GUIDANCE IS CONSISTENT IN INDICATING THE
TURN AROUND THE RIDGE AXIS THROUGH THE FIRST 72 HOURS BUT THEN
DIVERGES SHARPLY IN THE TAU 96 AND TAU 120 HOUR PERIODS. WHILE
DETERMINISTIC MODELS CONTINUE TO INDICATE A RECURVE SCENARIO, THE
VAST MAJORITY OF BOTH THE GFS AND ECMWF ENSEMBLES INDICATE THAT 27W 
DOES NOT QUITE COUPLE WITH THE MID-LATITUDE TROUGH AND REVERTS BACK 
TO WESTWARD MOVEMENT INTO THE PHILIPPINE SEA. THEREFORE, WHILE THERE 
IS GOOD CONFIDENCE IN THE TRACK AND INTENSITY THROUGH THE FIRST 72 
HOURS, THE CONFIDENCE DIVES SHARPLY AFTERWARDS.   

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