WDPN32 PGTW 040900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (BAILU) WARNING 
NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 37.4N 151.7E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 522 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 MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAPIDLY
DETERIORATING CIRCULATION, WITH ONE PRIMARY LOW LEVEL CIRCULATION
CENTER (LLCC) AND MULTIPLE SECONDARY VORTICES ROTATING AROUND THE
PRIMARY CENTER. THE LARGEST OF THE SECONDARY VORTICES CAN BE SEEN
TO HAVE DEVELOPED NORTHWEST OF THE LLCC, DIVING SOUTHWARD AND NOW
TURNING INWARD TOWARDS THE PRIMARY LLCC. OTHER, WEAKER VORTICES ARE
SEEN DEVELOPING TO THE NORTHWEST AND WILL LIKELY REPEAT THE CYCLE
OVER THE NEXT 12 HOURS. A 040717Z SSMIS 91GHZ IMAGE SHOWS JUST HOW
MUCH THE CIRCULATION HAS OPENED UP AND BECOME RAGGED OVER THE LAST
24 HOURS, AS WELL AS HOW MUCH DRY AIR IS FIRMLY POSITIONED OVER THE
WESTERN HALF OF THE CIRCULATION. ANIMATED WATER VAPOR IMAGERY SHOWS
A SHARP UPPER-LEVEL TROUGH JUST WEST OF THE LLCC, WHICH IS HAVING
SOME POSITIVE EFFECTS SUCH AS INCREASING THE DIVERGENT POLEWARD
OUTFLOW, BUT NOT ENOUGH TO OFFSET THE OTHERWISE NEGATIVE
ENVIRONMENTAL PARAMETERS SUCH AS VERY COOL SSTS, AND DRY AIR
INTRUSION. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE
BASED ON A PARTIALLY EXPOSED LLCC IN THE MSI. THE INITIAL INTENSITY
IS ASSESSED WITH HIGH CONFIDENCE, CONSISTENT WITH THE LOWER END OF
THE SUBJECTIVE AGENCY DVORAK FIX ESTIMATES NOTED BELOW AND
PERSISTENT WITH EARLIER ASCAT AND SMAP DATA INDICATING A SUB-GALE
STRENGTH WIND FIELD.

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

CURRENT STEERING MECHANISM: NORTHEASTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE SOUTHWEST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T1.5 - 25 KTS
   CIMSS SATCON: 43 KTS AT 040324Z
   CIMSS ADT: 39 KTS AT 040530Z
   CIMSS AIDT: 42 KTS AT 040530Z
   CIMSS D-MINT: 30 KTS AT 040248Z
   CIMSS D-PRINT: 29 KTS AT 040630Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 5-10 KTS
   SST: 24-25 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: 200MB TROF POSITIONED WEST OF THE LLLC,
DISORGANIZED CIRCULATION WITH MULTIPLE VORTICES. 

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 IS FORECAST TO
CONTINUE TRACKING GENERALLY EASTWARD OVER THE NEXT 24 HOURS, ALONG
THE NORTHERN SIDE OF AN EXTENSION OF THE STR CENTERED SOUTH OF
HONSHU. AS THE RIDGE MOVES FURTHER AWAY AND THE EXTENSION WEAKENS,
THE SYSTEM COULD TRACK A BIT SOUTH OF DUE EAST FOR SHORT TIME OVER
THE NEXT 24 HOURS. A WEAKNESS DEVELOPS IN THE RIDGE BY TAU 24, AND
TS 13W WILL SLOW DOWN AS THIS WEAKNESS MOVES SOUTH OF THE SYSTEM,
BEFORE A NEW RIDGE BUILDS IN FROM THE EAST. TRANSITION OF THE
STEERING INFLUENCE TO THE EASTERN RIDGE WILL OCCUR QUICKLY, AND TD
WILL BEGIN TO ACCELERATE TOWARDS THE NORTHEAST AROUND TAU 36. THE
200MB TROUGH WILL BE FAVORABLY POSITIONED RELATIVE TO THE LLCC FOR
THE NEXT 12 TO 24 HOURS AND WILL CONTINUE TO SUPPORT ENHANCED
POLEWARD OUTFLOW. BUT THIS WILL NOT BE ENOUGH TO OFFSET THE
OTHERWISE UNFAVORABLE CONDITIONS, AND THE SYSTEM IS FORECAST TO
MAINTAIN A FLAT INTENSITY PROFILE FOR THE NEXT 36 HOURS. THE UPPER
TROUGH WILL MOVE OUT AHEAD OF THE LLCC BETWEEN TAU 24 AND 36,
LEAVING TD 13W BEHIND, UNDER CONVERGENT FLOW ALOFT AND A DEEP POOL
OF DRY AIR ALOFT. THE REMNANT VORTEX WILL CONTINUE TO SLOWLY WEAKEN
THROUGH THE REMAINDER OF THE FORECAST PERIOD, WHILE SIMULTANEOUSLY
BEGINNING EXTRATROPICAL TRANSITION (ETT). COMPLETION OF ETT IS
ANTICIPATED NO LATER THAN TAU 72, AND LIKELY AS EARLY AS TAU 60. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN VERY GOOD
AGREEMENT THROUGH THE ENTIRE FORECAST PERIOD, WITH CROSS-TRACK
SPREAD INCREASING GRADUALLY TO JUST 115NM BY THE END OF THE
FORECAST PERIOD. ALONG-TRACK SPREAD INCREASES TO 200NM BY TAU 72.
THE JTWC FORECAST IS POSITIONED NEAR THE CONSENSUS MEAN THROUGH THE
FORECAST WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD
AGREEMENT, THOUGH IT WEAKENS THE SYSTEM TOO QUICKLY AND THE JTWC
FORECAST IS PLACED ABOUT 5 KNOTS HIGHER THAN THE CONSENSUS WITH
HIGH CONFIDENCE. 

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