WDPN32 PGTW 050300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (BAILU) WARNING 
NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 38.1N 157.2E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 755 NM EAST OF MISAWA, JAPAN
   MOVEMENT PAST 6 HOURS: EASTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
DEPRESSION (TD) 13W (BAILU) WITH A DEFINED PARTIALLY EXPOSED
LOW-LEVEL CIRCULATION CENTER (LLCC). A 042246Z METOP-B ASCAT IMAGE
REVEALED THAT THE CENTER IS STILL DISTINCT WITH A SWATH OF 30 KNOT
WINDS WITHIN THE SOUTHWESTERN QUADRANT. DRY AIR CONTINUES TO
HEAVILY IMPACT THE VORTEX, EVIDENT BY THE LACK OF DEEP CENTRAL
CONVECTION AND A FIELD OF STRATOCUMULUS CLOUDS WRAPPING INTO THE
SYSTEM FROM THE NORTH AND WEST. ENVIRONMENTAL ANALYSIS INDICATES
THAT 13W IS IN AN UNFAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG 
EASTWARD OUTFLOW ALOFT AND LOW TO MODERATE (15-20 KTS) VERTICAL WIND 
SHEAR, WHICH IS GREATLY OFFSET BY SIGNIFICANT DRY AIR ENTRAINMENT AND 
COOL (24-25 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 AND 
INTENSITY ARE BOTH PLACED WITH HIGH CONFIDENCE BASED ON THE MENTIONED 
ASCAT IMAGE. AGENCY DVORAK FIXES ALSO HELP SUPPORT THE INITIAL 
INTENSITY ASSESSMENT WITH THE MAJORITY OF AGENCIES REPORTING A T2.0 
CI (30 KTS) ON THE SYSTEM.

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 ADT: 34 KTS AT 050010Z
   CIMSS AIDT: 42 KTS AT 050010Z
   CIMSS D-PRINT: 27 KTS AT 050010Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 15-20 KTS
   SST: 24-25 CELSIUS
   OUTFLOW: STRONG EASTWARD
   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 BELOW 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
ALSO 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 129 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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