WDPN32 PGTW 041500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (THIRTEEN) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.7N 146.7E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 284 NM NORTHEAST OF CHICHI JIMA
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
CONSOLIDATING YET STRUGGLING TROPICAL DEPRESSION (TD) WITH FLARING
CONVECTION OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC). WATER
VAPOR IMAGERY REVEALS WEAK RADIAL OUTFLOW THAT IS DISTURBED BY A
NEARBY UPPER-LEVEL CYCLONE TO THE SOUTHWEST. THE CYCLONE ALSO
INTRODUCES DRY AIR TO THE CIRCULATION WRAPPING AROUND THE SOUTHERN
PERIPHERY FROM THE WEST. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE AFOREMENTIONED ANIMATED EIR. THE INITIAL
INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AGENCY AND OBJECTIVE FIXES LISTED BELOW.

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

CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 33 KTS AT 041130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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 ROUND THE AXIS OF THE
STR TO THE NORTHEAST FOR THE NEXT 24 HOURS BEFORE CONTINUING ON A
NORTHWESTWARD TRACK THROUGH THE END OF THE FORECAST PERIOD. THE
ENVIRONMENT WILL REMAIN MARGINALLY FAVORABLE FOR INTENSIFICATION
WITH AN UNFAVORABLE UPPER-LEVEL ENVIRONMENT THAT WILL BE INDUCED BY
A NEARBY SHORT-WAVE TROUGH THAT APPROACHES FROM THE NORTHWEST
BEFORE THE SYSTEM BECOMES EMBEDDED BETWEEN TAU 48-72. THE
ENCROACHING TROUGH WILL INITIATE EXTRATROPICAL TRANSITION, COUPLED
WITH COOL SEA SURFACE TEMPERATURES 24-25C) THAT TD 13W WILL PASS
OVER. BAROCLINIC FORCING WILL MAINTAIN THE INTENSITY OF 30 KTS
THROUGH THE END OF EXTRATROPICAL TRANSITION. IT IS POSSIBLE THAT
THE UPPER-LEVEL TROUGH MAY APPROACH SOONER THAN REFLECTED IN THE
FORECAST, THEREBY INITIATING EXTRATROPICAL TRANSITION EARLIER. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN TIGHT
AGREEMENT REGARDING THE FORECAST TRACK DIRECTION AND SPEED AS THE
SYSTEM ROUNDS THE STR AS REFLECTED IN A MAXIMUM ALONG-TRACK SPREAD
OF 90NM AND CROSS-TRACK SPREAD OF 50NM. BETWEEN ECMWF AND GFS, THE
APPROACH OF THE UPPER-LEVEL TROUGH VARIES. GFS DEPICTS A FASTER
APPROACH WHICH WOULD INITIATE EXTRATROPICAL TRANSITION EARLIER THAN
TAU 48, AND ECMWF DEPICTS A WEAK TROUGH INTERACTING BETWEEN TAU
60-72. THE JTWC INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE
SYSTEM WILL REMAIN BETWEEN 30-35KTS THROUGH THE END OF THE FORECAST
PERIOD, WITH THE EXCEPTION OF GFS WHICH DEPICTS A WEAKENING TO
25KTS THAT REMAINS CONSISTENT THROUGH TAU 72.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM//
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