WDPN32 PGTW 041500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (BAILU) WARNING 
NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 37.5N 153.9E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 617 NM EAST-SOUTHEAST OF MISAWA, JAPAN
   MOVEMENT PAST 6 HOURS: EASTWARD AT 17 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED PROXY VISIBLE (PROXYVIS) SATELLITE IMAGERY DEPICTS A FULLY
DECOUPLED SYSTEM, WITH A WELL-DEFINED LOW LEVEL CIRCULATION CENTER
(LLCC) DISPLACED TO THE WEST OF A MID- AND UPPER-LEVEL ROTATION
PUSHED OFF TO THE EAST. ANIMATED WATER VAPOR IMAGERY DEPICTS
UPPER-LEVEL CIRRUS DIVING SOUTHWARD TO THE WEST OF THE LLCC, THEN
TURNING SHARPLY NORTHEASTWARD IN THE IMMEDIATE VICINITY OF THE
CENTER, SUPPORTING THE CIMSS ATMOSPHERIC MOTION VECTOR (AMV)
ANALYSIS AS WELL AS THE ECMWF MODEL DEPICTION. THE UPPER-LEVEL
WINDS ARE FAIRLY STRONG BUT AREA IN PHASE WITH THE STORM MOTION,
WITH DEEP-LAYER SHEAR ESTIMATED AT ABOUT 10 KNOTS. MEANWHILE, THE
CIRA ADVECTED LAYER PRECIPITABLE WATER ANALYSIS DEPICTS A DEEP WEDGE 
OF DRY AIR ALONG THE WESTERN FLANK OF THE SYSTEM, HELPING KEEP
CONVECTIVE ACTIVITY TO A MINIMUM. A 041117Z ASCAT-C PASS REVEALS AN
ELONGATED LOW-LEVEL STRUCTURE, WITH A SECONDARY CIRCULATION
DEVELOPING TO THE EAST OF THE PRIMARY LLCC. 25-30 KNOT WINDS ARE
PRESENT ACROSS MOST OF THE SOUTHERN HEMISPHERE OF THE CIRCULATION
WITH LIGHTER WINDS ON THE NORTHERN FLANK. THE INITIAL POSITION AND
INTENSITY ARE ASSESSED WITH HIGH CONFIDENCE BASED ON THE PROXYVIS
IMAGERY AND ASCAT DATA RESPECTIVELY. ENVIRONMENTAL CONDITIONS ARE
INCREASINGLY UNFAVORABLE COOL SSTS AND DRY AIR INTRUSION OFFSETTING
STRONG POLEWARD OUTFLOW AND LOW SHEAR.

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

CURRENT STEERING MECHANISM: NORTHEASTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED SOUTHEAST OF HONSHU. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T1.5 - 25 KTS
   CIMSS SATCON: 42 KTS AT 040825Z
   CIMSS ADT: 32 KTS AT 041140Z
   CIMSS AIDT: 39 KTS AT 041140Z
   CIMSS D-MINT: 30 KTS AT 040738Z
   CIMSS D-PRINT: 26 KTS AT 041210Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 5-10 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: FULLY DECOUPLED VORTEX, DRY AIR OVER TOP OF THE
LLCC. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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: TROPICAL DEPRESSION (TD) 13W HAS TRAVELED
ALMOST DUE EASTWARD OVER THE LAST 6 HOURS OR SO, ALONG THE
NORTHEASTERN FLANK OF A RETROGRADING STR NOW POSITIONED SOUTHEAST
OF HONSHU. THE SYSTEM WILL IMMINENTLY BEGIN SLOWING DOWN AS IT
MOVES BY TO THE NORTH OF A COL-REGION BETWEEN THE STR SOUTH OF
HONSHU AND A SECOND STR BUILDING IN FROM NEAR THE DATELINE. AS TD
13W RUNS INTO THE NORTHWESTERN FLANK OF THIS EASTERN STR, AROUND
TAU 24, IT WILL TURN NORTHEASTWARD AND CONTINUE TO SLOW DOWN A BIT
AS IT MAKES THIS FIRST ENCOUNTER. AS THE RIDGE CONTINUES TO SLIDE
OFF TO THE SOUTHWEST, THE STEERING GRADIENT STRENGTHENS TO THE
SOUTHERN FLANK OF TD 13W, AND THE SYSTEM WILL ACCELERATE OFF
TOWARDS THE NORTHEAST AFTER TAU 36, CONTINUING THROUGH THE END OF
THE FORECAST PERIOD. THE 200MB TROF THAT IS CURRENTLY POSITIONED
JUST WEST OF TD 13W IS FORECAST TO CONTINUE TRACKING EASTWARD AT
ABOUT THE SAME SPEED AS TD 13W FOR THE NEXT 24 HOURS. THIS WILL
KEEP IT IN A GENERALLY FAVORABLE POSITION AND CONTINUE PROVIDING A
SOURCE OF DIVERGENT POLEWARD OUTFLOW, ALLOWING TD 13W TO HOLD ONTO
30 KNOT INTENSITY FOR JUST A BIT LONGER. BY TAU 24 HOWEVER, THE
TROF MOVES OUT AHEAD OF TD 13W, USHERING IN CONVERGENT FLOW ALOFT
AND EVEN MORE DRY AIR IN THE MID-LEVELS, AND TD 13W WILL WEAKEN
FURTHER DURING THIS TIMEFRAME. THE SYSTEM BEGINS EXTRATROPICAL
TRANSITION (ETT) AROUND TAU 36 AND SHOULD COMPLETE TRANSITION
AROUND TAU 60 OR SLIGHTLY EARLIER, THOUGH THE FORECAST IS EXTENDED
TO TAU 72 DUE TO FORECAST POINT CONSTRAINTS. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN TIGHT
AGREEMENT, WITH CROSS- AND ALONG-TRACK SPREAD INCREASING TO A
MODEST 100NM BY THE END OF THE FORECAST PERIOD. THE JTWC FORECAST
IS POSITIONED ALONG THE SOUTHERN EDGE OF THE GUIDANCE ENVELOPE
THROUGH THE FORECAST PERIOD WITH HIGH CONFIDENCE. INTENSITY
GUIDANCE IS IN GOOD AGREEMENT THAT THE SYSTEM WILL MAINTAIN
INTENSITY FOR ABOUT 24 HOURS BEFORE DROPPING ABOUT 5 KNOTS AND THEN
KEEPING STEADY AT 25 KNOTS THROUGH THE END OF THE FORECAST. THE
JTWC FORECAST IS PLACED AT THE CONSENSUS MEAN THROUGH TAU 72 WITH
HIGH CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: HIGH//
NNNN