WDPN32 PGTW 020300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (THIRTEEN) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.3N 136.9E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 281 NM WEST-NORTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A COMPACT
LOW-LEVEL CIRCULATION CENTER (LLCC) ASSOCIATED WITH TROPICAL
DEPRESSION (TD) 13W. THE SYSTEM HAS DEVELOPED ALONG A SOUTHEASTERLY
MONSOONAL FLOW AND IS CURRENTLY EMBEDDED IN A MARGINALLY FAVORABLE
ENVIRONMENT, CHARACTERIZED BY HIGH MOISTURE CONTENT THROUGHOUT THE
ATMOSPHERIC COLUMN, WARM (28-29 C) SEA SURFACE TEMPERATURES (SST),
LOW (0-5 KTS) VERTICAL WIND SHEAR (VWS) AND MODERATE POLEWARD 
OUTFLOW. THE ONLY CURRENT MAJOR DEVELOPMENT INHIBITOR IS A HUGE
SWATH OF DRY, DEEP-LAYER AIR TO THE WEST AND NORTHWEST. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A 012352 METOP-B
ASCAT PASS, IN CONJUNCTION WITH THE VISIBLE IMAGERY SHOWING A MOSTLY
EXPOSED LLCC. MAJORITY OF THE CONVECTIVE ACTIVITY IS LOCATED ALONG
THE SOUTHEASTERN PERIPHERY OF THE CIRCULATION, WITH LIMITED CENTRAL
CONVECTION. THE INITIAL INTENSITY OF 25 KTS IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE AFOREMENTIONED ASCAT, AS WELL AS THE AGENCY
DVORAK FIXES LISTED BELOW.

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

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.0 - 25 KTS
   RJTD: T1.5 - 25 KTS
   CIMSS D-PRINT: 22 KTS AT 020000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 0-5 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR TO THE WEST

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TD 13W IS FORECAST TO TRACK ALONG THE
NORTHWESTERN PERIPHERY OF A STR CENTERED TO THE EAST THROUGH THE
INITIAL 72 HOURS. DURING THAT TIME, ENVIRONMENTAL CONDITIONS WILL
REMAIN MARGINALLY FAVORABLE AND THE SYSTEM IS EXPECTED TO REACH A
MODEST PEAK INTENSITY OF 40 KTS AROUND TAU 48. SHORTLY AFTER TAU 72
HOWEVER, AND AS THE SYSTEM APPROACHES ANOTHER BUILDING STR TO THE
SOUTHEAST, IT WILL MAKE A SLIGHTLY POLEWARD TURN. COOLING SST AND
INCREASING DRY AIR ENTRAINMENT WILL RESULT IN A WEAKENING TREND, AS 
THE SYSTEM SIMULTANEOUSLY BEGINS EXTRATROPICAL TRANSITION (ETT).
TD 13W IS FORECAST TO FULLY DISSIPATE AT OR PRIOR TO TAU 120,
BEFORE IT COMPLETES THE ETT.

MODEL DISCUSSION: NUMERICAL TRACK MODEL GUIDANCE IS IN GOOD
AGREEMENT THROUGHOUT THE FORECAST PERIOD, WITH ALL MODELS AGREEING
ON THE GENERAL STEERING PATTERN. CROSS-TRACK SPREAD AT TAU 24 IS
ESTABLISHED AT 65 NM, WITH DETERMINISTIC GFS TRACKER BEING A PRIMARY 
OUTLIER SUGGESTING A WIDER TURN. TRACK GUIDANCE UNCERTAINTY INCREASES 
WITH TIME, AS WITNESSED BY AN INCREASE TO THE CROSS-TRACK SPREAD TO 
90 NM TOWARD THE END OF THE FORECAST PERIOD. JTWC INTENSITY FORECAST 
IS ASSESSED WITH OVERALL MEDIUM CONFIDENCE. WHILE ALL MODELS 
GENERALLY AGREE ON THE CONSENSUS TREND PATTERN OF SLIGHT 
INTENSIFICATION THROUGH TAU 48-72, FOLLOWED BY A WEAKENING
AFTERWARDS, THE INTENSITY UNCERTAINTY SPREAD IS AS HIGH AS 30 KTS
THROUGHOUT THE FORECAST. HAFS CURRENTLY OFFERS THE MOST
CONSERVATIVE GUIDANCE WITH PEAK JUST ABOVE 30 KTS, WHILE GFS-DRIVEN
COAMPS-TC IS THE MOST AGGRESSIVE, PREDICTING PEAK CLOSER TO 45 KTS.

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