WDPN33 PGTW 190900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (NANMADOL) 
WARNING NR 027//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 34.8N 132.4E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 33 NM NORTH-NORTHEAST OF IWAKUNI, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN EXPANDING
FIELD OF SHALLOWING CONVECTION SHEARING NORTHEASTWARD FROM AN
ELONGATING LOW-LEVEL CIRCULATION. THE INITIAL POSITION IS PLACED
WITH MEDIUM CONFIDENCE BASED ON RECENT SATELLITE FIXES FROM PGTW
AND RJTD AS WELL AS ANIMATED RADAR IMAGERY AND SYNOPTIC
OBSERVATIONS FROM JAPAN. THE INITIAL INTENSITY OF 55 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON SYNOPTIC OBSERVATIONS
AROUND THE CIRCULATION CENTER AND OFFSHORE WINDS EVIDENT IN THE
AFOREMENTIONED SCATTEROMETER AND AMSR2 WIND SPEED DATA. TS 16W HAS
MERGED WITH A SHORTWAVE TROUGH OVER THE PAST SIX HOURS AND IS
UNDERGOING EXTRATROPICAL TRANSITION, AS EVIDENT IN THE RAPIDLY
EVOLVING SATELLITE PRESENTATION. WEAKENING CONTINUES AS THE SYSTEM 
CONTENDS WITH INCREASING VERTICAL WIND SHEAR, PASSAGE OF THE SOUTHERN 
PORTION OF THE CIRCULATION OVER LAND AND PASSAGE OF THE NORTHERN 
PORTION OF THE CIRCULATION OVER UNFAVORABLY COOL WATER.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK, SCATTEROMETER DATA
AND WIND SPEEDS DERIVED FROM A 190347Z AMSR2 PASS

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) TO
THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   RJTD: T3.0 - 45 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 20-25 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 16W IS EXPECTED TO ACCELERATE
EAST-NORTHEASTWARD WITHIN A STRENGTHENING GRADIENT BETWEEN THE
CURRENT STEERING RIDGE AND A DIGGING A MID-LATITUDE TROUGH TO THE
NORTH. EXTRATROPICAL TRANSITION WILL COMPLETE BEFORE TAU 24 AS THE
SYSTEM FULLY MERGES WITH THE MID-LATITUDE TROUGH. WEAKENING IS
EXPECTED TO CONTINUE THROUGHOUT THE FORECAST PERIOD AS THE FLOW
PATTERN WILL NOT BE CONDUCIVE FOR REINTENSIFICATION. VERTICAL WIND
SHEAR, PASSAGE OVER LAND AND COOLER WATER AND A RAPID INFUSION OF
DRIER AIR FROM THE NORTH AND WEST WILL QUICKLY BREAK DOWN THE
CIRCULATION. HOWEVER, GALE FORCE WINDS CURRENTLY EXTEND FAR FROM
THE CIRCULATION CENTER AND WILL CONTINUE TO BRING GUSTY CONDITIONS
TO AREAS WITHIN AND AROUND MAINLAND JAPAN IN THE NEAR-TERM,
PARTICULARLY WITHIN AREAS ALONG THE SOUTHERN COAST OF HONSHU THAT
ARE PRONE TO TERRAIN-INDUCED ACCELERATION OF ONSHORE SOUTHERLY
FLOW.

MODEL DISCUSSION: NUMERICAL MODELS HAVE COME INTO CLOSER AGREEMENT
WITH RESPECT TO THE ANTICIPATED TRACK AND EXCELLENT AGREEMENT WITH
RESPECT TO THE ANTICIPATED INTENSITY. A FEW OF THE VORTEX TRACKERS
DERIVED FROM BOTH DETERMINISTIC AND ENSEMBLE MODEL SOLUTIONS LOOSE
THE CIRCULATION, BUT THE MAJORITY GROUPING INDICATES THAT THE SYSTEM
WILL HOLD TOGETHER AT LEAST UNTIL IT CROSSES THE EAST COAST OF
HONSHU BETWEEN TAU 12 AND TAU 24. AMONG THE MODEL SOLUTIONS IN THE
PRIMARY GROUPING, THE SPREAD IS PRIMARILY IN THE ALONG-TRACK
DIRECTION, LENDING HIGH CONFIDENCE TO THE ORIENTATION ALONG THE
NORTHERN COAST OF HONSHU AND MEDIUM CONFIDENCE IN THE TRACK OVERALL
DUE TO TRACK SPEED UNCERTAINTY. STRONG AGREEMENT AMONG MODEL
SOLUTIONS AND A RATHER STRAIGHTFORWARD WEAKENING WITH EXTRATROPICAL
TRANSITION SCENARIO LEND HIGH CONFIDENCE TO THE INTENSITY FORECAST.

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