WDPN32 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (BAILU) WARNING 
NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 38.0N 155.7E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 689 NM EAST OF MISAWA, JAPAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
DEPRESSION (TD) 13W (BAILU) WITH AN EXPOSED AND INCREASINGLY
ELONGATED LOW-LEVEL CIRCULATION CENTER (LLCC). DRY AIR CONTINUES TO
HEAVILY IMPACT THE VORTEX, CAUSING DEEP CONVECTION TO BE CONFINED
TO A SMALL REGION WITHIN THE NORTHEASTERN PERIPHERY. ENVIRONMENTAL
ANALYSIS INDICATES THAT 13W IS IN A MARGINALLY UNFAVORABLE
ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD OUTFLOW ALOFT, LOW
(10-15 KTS) VERTICAL WIND SHEAR, SIGNIFICANT DRY AIR ENTRAINMENT,
AND BORDERLINE (25-26 C) SEA SURFACE TEMPERATURES. THOUGH SHEAR IS
RELATIVELY LOW OVER THE TOP OF THE SYSTEM, SHEAR DRASTICALLY
INCREASES JUST NORTH OF THE LLCC, AROUND THE 40TH LATITUDE LINE.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
EXPOSED LLCC IN ANIMATED EIR IMAGERY. THE INITIAL INTENSITY OF 30
KTS IS ALSO ASSESSED WITH HIGH CONFIDENCE BASED ON THE CLOSE
AGREEMENT BETWEEN AGENCY DVORAK FIXES AND OBJECTIVE INTENSITY
ESTIMATES.

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

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) CENTERED TO THE SOUTHEAST.

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: 40 KTS AT 041545Z
   CIMSS ADT: 31 KTS AT 041740Z
   CIMSS AIDT: 39 KTS AT 041740Z
   CIMSS D-MINT: 29 KTS AT 041545Z
   CIMSS D-PRINT: 32 KTS AT 041740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 10-15 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: SIGNIFICANT DRY AIR ENTRAINMENT

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: 13W IS FORECAST TO TRACK GENERALLY
NORTHEASTWARD, ALONG THE NORTHWESTERN PERIPHERY OF THE SUBTROPICAL
RIDGE TO THE SOUTHEAST THROUGHOUT THE FORECAST PERIOD.
EXTRATROPICAL TRANSITION IS FORECAST TO BEGIN AT TAU 36 AND
COMPLETE NEAR TAU 48 AS THE SYSTEM BECOMES FURTHER EMBEDDED IN THE
MIDLATITUDE WESTERLIES AND SEA SURFACE TEMPERATURES DROP TO BE LOW
20 C. REGARDING INTENSITY, 13W IS FORECAST TO MAINTAIN INTENSITY
THROUGH TAU 24 AS SHEAR REMAINS RELATIVELY LOW. HOWEVER, AFTER TAU
24, WESTERLY SHEAR INCREASES TO OVER 30 KTS AND DRY AIR INTRUSION
INCREASES, CAUSING 13W TO WEAKEN AS IT COMPLETES EXTRATROPICAL
TRANSITION. THERE IS A CHANCE THAT THE VORTEX WASHES OUT AND
DISSIPATES PRIOR TO COMPLETING EXTRATROPICAL TRANSITION DUE TO THE
HOSTILE ENVIRONMENT 13W IS EXPECTED TO ENCOUNTER.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT WITH A 97 NM CROSS-TRACK SPREAD AT TAU 48 WITH MINIMAL
ALONG-TRACK SPREAD. THEREFORE, THE JTWC TRACK FORECAST IS PLACED
WITH HIGH CONFIDENCE. INTENSITY GUIDANCE AGREES THAT THE SYSTEM
WILL MAINTAIN INTENSITY OVER THE NEXT 24 HOURS BEFORE SLIGHTLY
WEAKENING. AS A RESULT, THE JTWC INTENSITY FORECAST IS ALSO PLACED
WITH HIGH CONFIDENCE, CLOSE TO THE MULTI-MODEL CONSENSUS.

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