Tropical Storm THIRTEEN Advisory Mi, 31.08.

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: 20.4N 132.4E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 445 NM SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN EXPOSED
LOW LEVEL CIRCULATION CENTER (LLCC) WITH FLARING DEEP CONVECTION
SHEARED TO THE SOUTHWEST DUE TO THE OUTFLOW FROM STY 12W, LOCATED
APPROXIMATELY 400NM TO THE NORTH-NORTHWEST. THE INITIAL POSITION IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC IN THE MSI,
WITH SUPPORT FROM EARLIER SCATTEROMETER DATA. THE INITIAL INTENSITY
OF 30 KNOTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE ADT FIX
AND THE EARLIER SCATTEROMETER DATA FROM AROUND 302200Z. OVERALL THE
ENVIRONMENT IS SOMEWHAT MARGINAL, WITH THE OUTFLOW FROM STY 12W
SMOTHERING THE SYSTEM AND KEEPING IT FROM CONSOLIDATING A
CONVECTIVE CORE, WHILE THE OTHER PARAMETERS SUCH AS SHEAR AND SSTS
REMAIN CONDUCIVE FOR INTENSIFICATION. HAVING BEEN CAPTURED BY STY
12W, THE SYSTEM IS MOVING NORTHWARD, BEING PULLED INTO THE LARGER
CIRCULATION ASSOCIATED WITH 12W, AS WELL AS MOVING ALONG THE
WESTERN SIDE OF THE STR TO THE EAST.
INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).
CURRENT STEERING MECHANISM: COMBINATION OF A SUBTROPICAL RIDGE
(STR) TO THE EAST AND BINARY INTERACTION WITH STY 12W TO THE NORTH.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T1.5 - 25 KTS
   CIMSS ADT: 30 KTS AT 302350Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: WEAK EQUATORWARD
   OTHER FACTORS: OUTFLOW FROM STY 12W
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: TD 13W IS FORECAST TO TRACK ALONG THE
PERIPHERY OF STY 12W, TRACING AN EVER-TIGHTENING CYCLONIC ARC
THROUGH THE SHORT FORECAST PERIOD. AS THE SYSTEM CLOSES WITHIN
200NM OF THE CENTER OF STY 12W, AROUND TAU 24 TO TAU 36, IT WILL
SLOWLY BEGIN TO BE ABSORBED WITH THE EXPANDING WIND FIELD
ASSOCIATED WITH STY 12W. FULL DISSIPATION AS A SEPARATE AND
DISTINCT CIRCULATION CENTER IS ANTICIPATED BY TAU 48. WHILE THE
UPPER-LEVEL OUTFLOW FROM STY 12W IS CURRENTLY INHIBITING THE
SYSTEM, AS TD 13W MOVES TO A POSITION DUE EAST OF STY 12W, AROUND
TAU 24, THE OUTFLOW ENVIRONMENT SHOULD IMPROVE DRAMATICALLY, AS
MODEL FIELDS SUGGEST LIMITED EASTWARD AND POLEWARD OUTFLOW FROM STY
12W AND DEVELOPMENT OF AN EQUATORWARD AND EASTWARD OUTFLOW CHANNEL
FOR TD 13W. THIS SHOULD ALLOW FOR A PERIOD OF INTENSIFICATION TO A
PEAK OF 40 KNOTS BY TAU 36. WHILE THE SYSTEM IS FORECAST TO BE
ABSORBED INTO STY 12W, THE INTENSITY AT THIS TIME IS ANTICIPATED TO
REMAIN AT 40 KNOTS. THE HWRF-P MODEL HAS CONSISTENTLY (OVER THE
PAST FOUR CYCLES) SUGGESTED AN ALTERNATE SCENARIO, WHICH WHILE LOW
PROBABILITY, BEARS MENTIONING DUE TO HWRFS PERISTENCE. IN THE HWRF
SOLUTION, TD 13W IS ABLE TO DEVELOP AND MAINTAIN A VERY SMALL,
DISTINCT CIRCULATION CENTER, TAP INTO GOOD DIVERGENT OUTFLOW AND
RAPIDLY INTENSIFY TO WELL TO TYPHOON STRENGTH BEFORE TAU 48, THEN
WRAP THIS DISTINCT SYSTEM ALL THE WAY AROUND STY 12W.
MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH THE
FORECAST PERIOD, WITH THE EXCEPTION OF THE GALWEM WHICH MERGES THE
SYSTEM INTO STY 12W TO THE SOUTH OF THE CIRCULATION OF STY 12W,
WHICH IS HIGHLY UNLIKELY. THE REMAINDER OF THE GUIDANCE CURVES THE
TRACK AROUND THE EASTERN SIDE AND MERGES ON THE NORTHERN SIDE OF
THE ENVELOPE. HOWEVER, BINARY INTERACTIONS ARE NOTORIOUSLY
CHALLENGING FOR MODELS TO HANDLE, AND THUS THERE IS ONLY MEDIUM
CONFIDENCE IN THE FORECAST TRACK. INTENSITY GUIDANCE REMAINS HIGHLY
DIVERGENT AND UNCERTAIN, WITH A VERY LARGE SPREAD IN POSSIBLE
SOLUTIONS, RANGING FROM 35 KNOTS FOR THE DECAY SHIPS, TO OVER 100
KNOTS IN THE HWRF (AFTER TAU 48, SEE ALTERNATE SCENARIO ABOVE). THE
JTWC FORECAST REMAINS CONSISTENT WITH THE CONSENSUS MEAN THROUGH
THE SHORT-TERM FORECAST LENGTH, BUT WELL BELOW THE HWRF AND
COAMPS-TC SOLUTIONS WHICH PEAK THE SYSTEM AT 65 KNOTS AT TAU 48. IN
LIGHT OF THE ALTERNATE SCENARIO AND THE AGGRESSIVE MESOSCALE MODEL
SOLUTIONS, THE INTENSITY FORECAST IS ASSESSED WITH LOW CONFIDENCE.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: LOW//
NNNN
NNNN