WDPN32 PGTW 020900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (THIRTEEN) 
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.0N 138.6E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 241 NM NORTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 17 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A BROAD,
ELONGATED AND COMPLEX ROTATION WITH MULTIPLE LOW-LEVEL VORTICES
ROTATING ABOUT A CENTROID. THE PRIMARY LOW LEVEL CIRCULATION CENTER
(LLCC) IS BEING TRACKED AS THE INITIAL POSITION, WHILE A SECONDARY
CIRCULATION IS WELL-DEFINED APPROXIMATELY 135NM TO THE NORTH,
HAVING RACED NORTHWARD OVER THE LAST SIX HOURS. THE TERTIARY
ROTATION IS POSITIONED JUST WEST OF THE PRIMARY ROTATION AND IS
BEING ABSORBED INTO THE MAIN LLCC. A 020617Z SSMIS 91GHZ MICROWAVE
IMAGE REVEALS A LARGE OVERALL ROTATION WITH MULTIPLE EMBEDDED
ROTATIONS. FRAGMENTED BANDS OF MODERATE CONVECTION SURROUND THE
LLCC AND ARE SEPARATED FROM A SMALL BALL OF CONVECTION ASSOCIATED
WITH THE SECONDARY ROTATION TO THE NORTH. ANIMATED WATER VAPOR
IMAGERY AND JTWC HAND ANALYSIS SHOW A SHARP UPPER-LEVEL RIDGE AXIS
POSITIONED JUST EAST OF THE SYSTEM AND AN UPPER-LEVEL LOW IN THE
VICINITY OF OKINAWA. THE INITIAL POSITION IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE MICROWAVE IMAGE NOTED ABOVE AND THE MSI
DEPICTION. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES NOTED
ABOVE AND CONSISTENT WITH EARLIER SCATTEROMETER DATA. ENVIRONMENTAL
CONDITIONS ARE MARGINALLY FAVORABLE WITH LOW VWS, GOOD POLEWARD
OUTFLOW AND WARM SSTS, OFFSET BY THE HIGHLY ASYMMETRIC NATURE OF
THE WIND FIELD AND THE PRESENCE OF MULTIPLE VORTICES.

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

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED EAST OF IWO TO. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T1.5 - 25 KTS
   CIMSS ADT: 28 KTS AT 020540Z
   CIMSS AIDT: 32 KTS AT 020540Z
   CIMSS D-MINT: 26 KTS AT 020617Z
   CIMSS D-PRINT: 25 KTS AT 020640Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: HIGHLY ASYMMETRIC WIND FIELD, AND MULTIPLE
VORTICES. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   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 NORTHEASTWARD ALONG THE WESTERN SIDE OF THE LARGE
STR OVER THE NEXT 36 HOURS. THE TRACK WILL FLATTEN OUT TO A MORE
EASTWARD TRAJECTORY FROM ABOUT TAU 48 TO TAU 72 AS THE STR SLIDES
RAPIDLY TO THE SOUTHWEST AND TD 01W TRACKS ALONG ITS NORTHERN
PERIPHERY. THE TRACK IS EXPECTED TO SHIFT TO NORTHEASTWARD AGAIN
AFTER TAU 72, AS ANOTHER STR MOVING WEST OF THE DATELINE TAKES OVER
AS THE PRIMARY STEERING MECHANISM. WHILE ENVIRONMENTAL CONDITIONS
OVERALL ARE QUITE FAVORABLE FOR INTENSIFICATION, THE FACT THAT THE
SYSTEM IS VERY DISORGANIZED MEANS THAT LITTLE TO NO INTENSIFICATION
IS EXPECTED IN THE NEXT 12 HOURS. SOME MODEL GUIDANCE SUGGESTS
MERGER OF THE TWO MAIN VORTICES WITHIN THE NEXT 12 HOURS FOLLOWED
BY A VORTEX ALIGNMENT AS THE SYSTEM MOVES OVER THE VERY WARM WATERS
OF KUROSHIO CURRENT EAST OF TOKYO. COUPLED WITH VERY GOOD POLEWARD
OUTFLOW INTO THE BASE OF A 200MB JET MAX EAST OF HOKKAIDO, THE
SYSTEM WILL EXPERIENCE A BRIEF BURST OF ADDITIONAL INTENSIFICATION
THROUGH TAU 48. HOWEVER, SHEAR IS EXPECTED TO RAPIDLY INCREASE
AFTER TAU 48, USHERING IN A WEDGE OF DRY AIR AS WELL, LEADING TO A
STEADY WEAKENING TREND AFTER TAU 48. THE SYSTEM WILL BEGIN
EXTRATROPICAL TRANSITION BY THE END OF THE FORECAST. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT
THROUGH THE FORECAST PERIOD, WITH 175NM CROSS-TRACK SPREAD AT TAU
72, OPENING UP TO 260NM BY THE END OF THE FORECAST PERIOD. THE JTWC
FORECAST IS POSITIONED CLOSE TO THE ECMWF DETERMINISTIC TRACKER
THROUGH THE FORECAST PERIOD, WITH HIGH CONFIDENCE. INTENSITY
GUIDANCE IS MIXED, WITH THE HAFS-A AND COTC SHOWING SLOW BUT STEADY
WEAKENING THROUGH THE ENTIRE FORECAST, WHILE THE CTCX AND
DECAY-SHIPS GUIDANCE SHOW STEADY TO NEAR-RAPID INTENSIFICATION
THROUGH TAU 60, TO A PEAK BETWEEN 45-55 KNOTS, FOLLOWED BY RAPID
WEAKENING. THE JTWC FORECAST IS POSITIONED SLIGHTLY ABOVE THE
CONSENSUS MEAN, BUT BELOW THE MOST AGGRESSIVE GUIDANCE WITH MEDIUM
CONFIDENCE. HIGHER INTENSITIES ARE POSSIBLE, ESPECIALLY IF THE
SYSTEM CAN CONSOLIDATE A LOW-LEVEL STRUCTURE RAPIDLY AND TAKE
ADVANTAGE OF THE OTHERWISE FAVORABLE ENVIRONMENT.  

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