WDPN33 PGTW 091500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 14W (CHAN-HOM) WARNING 
NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 32.3N 150.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 577 NM EAST-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 01 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED PROXY VISIBLE (PROXYVIS) SATELLITE IMAGERY DEPICTS A FULLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC), WITH NEWLY DEVELOPING,
MODERATE CONVECTION IN THE NORTHEASTERN QUADRANT, ALONG A LINE OF
CONVERGENCE. SINCE 0600Z THE LLCC HAS TRACKED SOUTH-SOUTHEASTWARD
BEFORE TURNING SHARPLY NORTH AND RETURNING TO ITS 0600Z POSITION BY
THE 1200Z HOUR, MAKING THE BEST TRACK APPEAR TO BE STATIONARY. IN
THE SUBSEQUENT TWO HOURS, THE SYSTEM HAS BEGUN TO MOVE OUT TO THE
NORTHWEST. A 090954Z ASCAT-B PASS SHOWED THE SYSTEM IS BARELY
HOLDING ONTO TROPICAL STORM STATUS, WITH THE VAST MAJORITY OF THE
VISIBLE WIND FIELD BEING 30-35 KNOTS. ANIMATED WATER VAPOR IMAGERY,
ATMOSPHERIC MOTION VECTOR (AMV) ANALYSIS AND MODEL FIELD DATA SHOW
AN ULL POSITIONED JUST NORTH OF THE LLCC, WITH A TROUGH EXTENDING
TO THE EAST. ALSO EVIDENT IN THE WATER VAPOR IMAGERY IS A LARGE
DEFORMATION ZONE EAST OF HONSHU AND A STRONG UPPER-LEVEL TROUGH
CURRENTLY MOVING ACROSS HONSHU. THE PROXIMITY OF THE ULL IS
INTRODUCING UPPER-LEVEL CONVERGENT FLOW ALOFT OVER TS 14W, AS WELL
AS BRINGING IN DRY MID-LEVEL AIR AND MODERATE NORTHWESTERLY SHEAR,
INHIBITING DEVELOPMENT. SSTS AND UPPER-LEVEL OUTFLOW CONDITIONS
REMAIN GENERALLY FAVORABLE BUT ARE MORE THAN OFFSET BY THE
UNFAVORABLE CONDITIONS DISCUSSED ABOVE. THE INITIAL POSITION IS
ASSESSED WITH HIGH CONFIDENCE USING THE EXPOSED LLCC IN THE
PROXYVIS IMAGERY. THE INITIAL INTENSITY IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE SCATTEROMETER DATA PRESENTED ABOVE.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WEAK STEERING PATTERN. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS ADT: 25 KTS AT 091200Z
   CIMSS AIDT: 27 KTS AT 091200Z
   CIMSS D-MINT: 35 KTS AT 090830Z
   CIMSS D-PRINT: 31 KTS AT 091130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 10-15 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: WEAK EASTWARD
   OTHER FACTORS: PROXIMITY OF AN UPPER-LEVEL LOW (ULL) JUST NORTH
OF THE SYSTEM. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 12W HAS NOW STARTED TO MOVE OUT OF THE WEAK
STEERING ENVIRONMENT, AND ACCELERATE NORTHWESTWARD ALONG THE
STRENGTHENING GRADIENT ALONG THE SOUTHWESTERN FLANK OF A LOW- TO
MID-LEVEL SUBTROPICAL RIDGE (STR) CENTERED SOUTHWEST OF THE
ALEUTIANS. THE NORTHWESTWARD TRAJECTORY IS FORECAST TO CONTINUE
THROUGH TAU 36, BEFORE THE TRACK TURNS SHARPLY WESTWARD IN RESPONSE
TO THE RIDGING BUILDING IN FROM THE WEST, MERGING WITH THE RIDGE
SOUTHWEST OF THE ALEUTIANS, FORMING A SINGLE RIDGE EXTENDING FROM
NORTH KOREA, OVER SAKHALIN ISLAND TO SOUTHEAST OF KAMCHATKA. THE
SYSTEM IS FORECAST TO MAKE LANDFALL ALONG THE EASTERN COAST OF
HONSHU JUST AROUND TAU 48. AFTER MAKING LANDFALL, THE EXACT
ORIENTATION OF THE RIDGE TO THE WEST, EXTENDING ROUGHLY FROM NORTH
KOREA TO FAR EASTERN RUSSIA, WILL DETERMINE THE TRACK THAT TS 14W
TAKES. THE ECMWF DEPICTS A MORE NORTHEASTWARD AXIS OF THE RIDGE
WHICH RESULTS IN A WEST-SOUTHWEST TRAJECTORY, TAKING IT OVER TOKYO.
THE BULK OF THE OTHER GLOBAL AND ENSEMBLE MODELS SHOW A FLATTER
RIDGE PATTERN, WHICH RESULTS IN A MORE WESTWARD TRAJECTORY ACROSS
JAPAN AND INTO THE SEA OF JAPAN. THE FORECAST MORE CLOSELY FOLLOWS
THE SECOND SCENARIO, WITH THE SYSTEM EMERGING INTO THE SOJ WEST OF
KANAZAWA, JAPAN BY TAU 60, BEFORE GRADUALLY TURNING SOUTHWESTWARD,
MAKING A SECOND LANDFALL NEAR POHANG, SOUTH KOREA BY THE END OF THE
FORECAST PERIOD. REGARDING INTENSITY, THE PROXIMITY OF THE ULL WILL
CONTINUE TO INHIBIT DEVELOPMENT IN THE SHORT-TERM. AFTER TAU 18,
THE TROUGH CURRENTLY MOVING OVER JAPAN WILL CUT OFF INTO AN ULL
WHICH DRIVES SOUTH ALONG THE EAST COAST OF HONSHU, ULTIMATELY
MOVING INTO A POSITION SOUTHWEST OF TS 14W, OPENING UP A ROBUST
POLEWARD OUTFLOW CHANNEL. AT THE SAME TIME, THE SYSTEM WILL BE
MOVING OVER THE WARM TONGUE ASSOCIATED WITH THE KUROSHIO CURRENT,
SUPPORTING INTENSIFICATION UP TO A PEAK OF 50-55 KNOTS BY TAU 36. THE
ULL MOVES SOUTHEAST OF TS 14W RAPIDLY, WHILE THE SYSTEM MOVES OVER
THE OYASHIO CURRENT ALONG THE COAST OF JAPAN, RESULTING IN
WEAKENING PRIOR TO LANDFALL. TERRAIN INTERACTION WILL FURTHER
WEAKEN TS 14W BEFORE IT MOVES INTO THE SOJ. THE SYSTEM BEGINS
SUBTROPICAL TRANSITION (STT) BY TAU 60, AND WILL COMPLETE STT BY
TAU 72 AS IT ALSO WEAKENS AND DISSIPATES PRIOR TO LANDFALL IN KOREA. 

MODEL DISCUSSION: THE OVERALL GUIDANCE PACKAGE CONTINUES TO SHIFT
SOUTHWARD WITH EACH NEW MODEL RUN, THOUGH THE ENSEMBLE MEMBER
DISPERSION IS DECREASING. AS MENTIONED ABOVE, THE ECMWF REMAINS A
SOUTHERN OUTLIER, TAKING THE CENTER OF THE SYSTEM OVER TOKYO. THE
REMAINDER OF THE MODELS ARE CONFINED TO A 110NM WIDE ENVELOPE
ROUGHLY CENTERED ON THE JTWC FORECAST TRACK. THE OVERALL TRACK
ENVELOPE REMAINS THE SAME THROUGH THE REMAINDER OF THE FORECAST.
THE JTWC FORECAST IS PLACED NEAR THE AI CONSENSUS MEAN, WITH MEDIUM
CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT WITH A STEADY
INTENSITY FOR 12 HOURS, FOLLOWED BY A BURST OF INTENSIFICATION
THROUGH TAU 36, FOLLOWED BY RAPID WEAKENING THROUGH THE REMAINDER
OF THE FORECAST. THE JTWC INTENSITY FORECAST IS SET NEAR THE
CONSENSUS MEAN WITH MEDIUM CONFIDENCE. 

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