WDPN33 PGTW 231500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 11W (NEPARTAK) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.0N 148.6E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 821 NM SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN AREA
OF EXPANDING DEEP CONVECTION SHEARED TO THE EAST OF A BROAD,
EXPOSED LOW-LEVEL CIRCULATION (LLC). A 230945Z GMI 89GHZ COMPOSITE
MICROWAVE IMAGE REVEALS SHALLOW BANDING WRAPPING LOOSELY AROUND THE
BROAD LLC WITH A WEAKLY DEFINED CENTER; DEEP CONVECTION IS
DISORGANIZED OVER THE EASTERN QUADRANT. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON A 231021Z ASCAT-A IMAGE. TD
11W IS CURRENTLY ASSESSED AS A SUBTROPICAL SYSTEM AND IS LOCATED
WITHIN THE SOUTHERN, DIVERGENT REGION OF A DEEP SUBTROPICAL TROUGH
WITH STRONG VENTING TO THE EAST AND SOUTHEAST AND STRONG VERTICAL
WIND SHEAR FUELING STRONG CONVECTIVE BURSTS OVER THE EASTERN AND
SOUTHEASTERN PERIPHERIES. THE INITIAL INTENSITY OF 30 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON A 231021Z ASCAT-A IMAGE
SHOWING AN ELONGATED CIRCULATION WITH A HIGHLY ASYMMETRIC WIND
FIELD TYPICAL WITH SUBTROPICAL CYCLONES; THIS IMAGE INDICATES A 
SWATH OF CONVERGENT SOUTHERLY WINDS OVER THE EASTERN QUADRANT WITH 
30-35 KNOT WINDS AND 10-20 KNOT WINDS OVER THE WESTERN SEMICIRCLE. A 
PGTW SUBTROPICAL FIX OF ST1.5 (25-30 KNOTS) ALSO SUPPORTS THE
ASSESSMENT.

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

CURRENT STEERING MECHANISM: NORTH-SOUTH ORIENTED SUBTROPICAL RIDGE
(STR) 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: ST1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
   OTHER FACTORS: SIGNIFICANT DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. TD 11W IS ASSESSED AS
A SUBTROPICAL CYCLONE.

FORECAST DISCUSSION: TD 11W WILL REMAIN A SUBTROPICAL CYCLONE
THROUGH THE FORECAST PERIOD. IT WILL NOT DEVELOP AS A TYPICAL
TROPICAL CYCLONE WITH CENTRAL, CONSOLIDATING CONVECTION AND A
CONTRACTING, STRENGTHENING WIND FIELD. THIS CRITICAL DISTINCTION
IS IMPORTANT TO KEEP IN MIND AS THE SYSTEM APPROACHES AND MAKES
LANDFALL OVER HONSHU. TD 11W IS CURRENTLY POSITIONED OVER THE
SOUTHERN PERIPHERY OF A DEEP UPPER-LEVEL SUBTROPICAL TROUGH AND IS
FORECAST TO TRACK POLEWARD WITHIN AN AREA OF ENHANCED FLOW BETWEEN
A DEVELOPING UPPER-LEVEL LOW AND THE NORTH-SOUTH ORIENTED STR. TD
11W SHOULD SLOWLY INTENSIFY TO A PEAK OF 50 KNOTS BY TAU 36 TO 48
DUE TO THE STRONG POLEWARD OUTFLOW ASSOCIATED WITH THE DEEPENING
UPPER LOW TO THE WEST. UPPER-LEVEL WINDS ARE EXPECTED TO INCREASE
TO JET STRENGTH ALONG THE EASTERN FLANK OF THIS LOW WITH VWS
INCREASING TO 40-45 KNOTS. CONSEQUENTLY, THE SYSTEM WILL BE UNABLE
TO SUSTAIN ANY TYPE OF CENTRALIZED CONVECTION AND WILL REMAIN
SUBTROPICAL IN NATURE WITH SIGNIFICANT DRY AIR ENTRAINMENT. AFTER
TAU 48, TD 11W WILL TRACK GENERALLY NORTHWESTWARD ALONG THE
SOUTHWEST PERIPHERY OF THE STR WHILE GRADUALLY WEAKENING AS IT
APPROACHES HONSHU DUE TO SLIGHTLY COOLER SST VALUES (26-27C), WEAK
OUTFLOW AND DRY AIR ENTRAINMENT.         

MODEL DISCUSSION: DUE TO THE COMPLEX SYNOPTIC STEERING ENVIRONMENT
AND INTERACTION WITH INITIALLY AN UPPER-LEVEL SUBTROPICAL TROUGH
THEN A STRONG UPPER-LEVEL LOW EAST OF HONSHU, THERE IS A LARGE DEGREE
OF UNCERTAINTY IN THE FORECAST TRACK WITH NUMERICAL MODEL GUIDANCE
SHOWING A LARGE SPREAD OF 400-450NM IN THE EXTENDED PERIOD THUS
THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK. DUE TO THE
SUBTROPICAL NATURE OF THIS SYSTEM THROUGH ITS LIFECYCLE, THERE IS
LOW CONFIDENCE IN THE JTWC INTENSITY FORECAST.  

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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