WDPN31 PGTW 141500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 01W (ONE) WARNING NR 
001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 9.3N 130.6E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 254 NM WEST-NORTHWEST OF KAYANGEL
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
DEPRESSION (TD) 01W WITH A RELATIVELY DISORGANIZED LOW-LEVEL 
CIRCULATION CENTER AND FLARING CONVECTION THROUGHOUT THE NORTHERN 
SEMICIRCLE. DRY AIR APPEARS TO BE WRAPPING INTO THE SOUTHERN
QUADRANT, KEEPING THE REGION MOSTLY CONVECTION FREE, REVEALING
LOW-LEVEL CLOUD LINES WRAPPING LAZILY BENEATH THE AFOREMENTIONED
CONVECTION DIRECTLY TO THE NORTH. ALOFT, ROBUST POLEWARD OUTFLOW
HAS BEEN EVIDENT OVER THE LAST FEW HOURS, WITH ASSOCIATED CIRRIFORM
TRANSVERSE BANDING BURSTING NORTHWARD AND AWAY FROM TD 01W. THE
ENVIRONMENT IS ASSESSED AS MARGINALLY FAVORABLE DUE TO VERTICAL
WIND SHEAR (VWS) EXCEEDING 15 KTS, WARM SEA SURFACE TEMPERATURES
(SST) RANGING BETWEEN 28-29 C, AND SUPPORTIVE UPPER-LEVEL OUTFLOW.
THE INITIAL POSITION AND INTENSITY HAS BEEN ASSESSED WITH HIGH
CONFIDENCE BASED ON A 141238Z METOP-B ASCAT PASS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE LOCATED
DIRECTLY TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.5 - 25 KTS
   CIMSS D-MINT: 17 KTS AT 140852Z
   CIMSS D-PRINT: 17 KTS AT 141200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TD 01W IS FORECASTED TO TRACK NORTHWESTWARD
OVER THE NEXT 72 HOURS, ALONG THE SOUTHWESTERN AND WESTERN
PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE LOCATED TO THE EAST.
DURING THE SAME TIME, AN ADDITIONAL SUBTROPICAL RIDGE TO WEST,
CENTERED OVER VIETNAM WILL BEGIN BUILDING EASTWARD, SLOWING THE
EVENTUAL NORTHEASTWARD TURN BETWEEN TAU 72 AND TAU 96 DUE TO
COMPETING STEERING FLOWS. FOLLOWING TAU 96, TD 01W IS EXPECTED TO
SLOWLY TRACK NORTHWESTWARD THROUGH THE REMAINDER OF THE FORECAST
PERIOD AS THE SUBTROPICAL RIDGE CENTERED TO THE EAST OF TD 01W
BEGINS TO WEAKEN AND RETRACT EASTWARD, CLEARING A WAY FOR 
THE AFOREMENTIONED NORTHEASTWARD TRACK BETWEEN TAU 96 AND TAU 120.
REGARDING INTENSITY, TD 01W IS FORECASTED TO SLOWLY INTENSIFY
THROUGHOUT THE NEXT 48 HOURS WITH SUPPORT FROM A ROBUST UPPER-LEVEL
OUTFLOW CHANNEL AND WARM SST GREATER THAN 26 C. THE LIMITING FACTOR
AT THIS TIME IS AN EXTREMELY DRY REGION OF AIR THAT IS FORECASTED TO
REMAIN WEDGED AGAINST THE SYSTEMS WESTERN FLANK, AND SLOWLY WRAP
INTO THE CORE WITH PERSISTENT MODERATE VERTICAL WIND SHEAR BETWEEN
15-20 KTS. FOLLOWING TAU 48, VERTICAL WIND SHEAR IS FORECASTED TO
INCREASE ABOVE 20 KTS, BEGINNING THE INITIAL WEAKENING TREND INTO
THE REMAINDER OF THE FORECAST PERIOD WITH ASSISTANCE FROM THE DRY
AIR TO THE WEST. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGHOUT THE INITIAL 72 HOURS OF THE FORECAST PERIOD,
DURING THE SYSTEMS NORTHWESTWARD TRACK. THE CROSS-TRACK SPREAD IS
119 NM BETWEEN ALL JTWC CONSENSUS MEMBERS, WITH THE ECMWF ENSEMBLE
SOLUTION ILLUSTRATING THE WESTERNMOST TRACK. FOLLOWING TAU 72, ALL
JTWC CONSENSUS MEMBERS CHARACTERIZE THE BEGINNING OF A NORTHEASTWARD 
TRACK, HOWEVER, THE SPEED AT WHICH THE SYSTEM SLOWS AND BEGINS THE 
NORTHEASTWARD TRACK DIFFERS BETWEEN EACH MEMBER. THEREFORE, THE JTWC 
FORECAST TRACK IS ALIGNED CLOSELY WITH THE MULTI-MODEL CONSENSUS, 
LENDING MEDIUM CONFIDENCE TO THE TRACK FORECAST. REGARDING INTENSITY, 
THE MAJORITY OF JTWC INTENSITY CONSENSUS MEMBERS SHOW A SLOW AND 
GRADUAL INCREASE IN INTENSITY OVER THE NEXT 72 HOURS. THE SHARPEST 
INCREASE IN INTENSITY IS HELD BY THE GFS DETERMINISTIC SOLUTION, 
ALTHOUGH IT IS LIMITED TO JUST UNDER 40 KTS BY TAU 12. HAFS 
ILLUSTRATES THE HIGHEST MAXIMUM INTENSITY NEAR TAU 60, CAPPING AT 55 
KTS. THE JTWC INTENSITY FORECAST HAS BEEN ASSESSED WITH MEDIUM 
CONFIDENCE THROUGHOUT THE FORECAST PERIOD, AND ALIGNED JUST ABOVE THE 
JTWC MULTI-MODEL CONSENSUS.

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