WDPN31 PGTW 090300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (FOUR) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 8.7N 152.1E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 73 NM NORTH OF CHUUK
   MOVEMENT PAST 6 HOURS: WESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS LOOSELY
ORGANIZED CLOUD BANDS WRAPPING INTO A MID-LEVEL CIRCULATION THAT IS
OFFSET TO THE NORTH-NORTHWEST OF THE ASSESSED LOW-LEVEL CIRCULATION
CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE 
BASED ON THE ANIMATED MSI AND SURFACE OBSERVATIONS FROM CHUUK. THE 
INITIAL INTENSITY OF 25 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED 
ON PARTIAL METOP-B ASCAT PASSES THAT REVEALED SWATHS OF 20-25 KT WINDS 
IN THE OUTER EDGES OF THE CIRCULATION, AS WELL AS AGENCY DVORAK FIXES 
RANGING FROM T1.0-2.0. THE ENVIRONMENT IS ASSESSED TO BE FAVORABLE FOR 
CONTINUED DEVELOPMENT OF 04W, WITH WARM (28-29 C) SEA SURFACE 
TEMPERATURES, LOW VERTICAL WIND SHEAR, ABUNDANT MID-LEVEL MOISTURE 
AVAILABILITY, AND MODERATE POLEWARD OUTFLOW ALOFT.

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

CURRENT STEERING MECHANISM: A WEAK STEERING ENVIRONMENT WITH A
WESTWARD EXTENSION OF A NEAR-EQUATORIAL RIDGE IN THE CENTRAL NORTH
PACIFIC AND THE EASTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE
CENTERED OVER THE LUZON STRAIT.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.0 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS D-PRINT: 30 KTS AT 080000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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.

FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 04W HAS BECOME
INCREASINGLY ORGANIZED OVER THE PAST 12 HOURS AS IT HAS SLOWLY
TRACKED NORTHWESTWARD. THE TRAJECTORY OF THE SYSTEM IS FORECAST TO
CONTINUE IN A GENERALLY NORTHWESTWARD DIRECTION TOWARD GUAM FOR THE
ENTIRE FORECAST PERIOD. THERE ARE SIGNIFICANT FORECAST CHALLENGES
IN REGARDS TO THE EXACT TRACK THAT IS EXPECTED, AS THERE IS LITTLE
CONSENSUS AMONG FORECAST GUIDANCE ABOUT WHICH OF THE COMPETING
STEERING INFLUENCES WILL ULTIMATELY CONTROL THE SYSTEM TRACK. A
NEAR-EQUATORIAL RIDGE TO THE EAST HAS THE POTENTIAL TO STEER 04W IN
A RECURVING ARC WITH A LARGER NORTHWARD COMPONENT, WHILE A
DEEP-LAYER SUBTROPICAL RIDGE TO THE WEST WOULD MAINTAIN A MORE
NORTHWESTWARD TRACK IF IT IS ABLE TO EXTEND TO THE NORTH OF 04W.
THE JTWC FORECAST TRACK IS PLACED ON A TRAJECTORY THAT FAVORS THE
LATTER STEERING MECHANISM, WHICH TRACKS THE SYSTEM SOUTHWEST OF
GUAM WITH A CPA OF 31 NM SHORTLY BEFORE TAU 120. THERE REMAINS A
HIGH LEVEL OF UNCERTAINTY IN THE TRACK AT THIS TIME, LENDING LOW
CONFIDENCE TO THE FORECAST. THE INTENSITY FORECAST PROJECTS STEADY
INTENSIFICATION THROUGH THE ENTIRE FORECAST PERIOD, UP TO 95 KTS AT
TAU 120. THE CURRENT FAVORABLE ENVIRONMENTAL CONDITIONS ARE
EXPECTED TO DEGRADE IN THE NEAR TERM WITH INCREASING MID-LAYER VWS
THAT WILL PLACE A LIMIT ON THE RATE OF INTENSIFICATION THROUGH
AROUND TAU 60. FURTHER INTENSIFICATION AFTER TAU 60 IS EXPECTED IN
A MORE FAVORABLE SHEAR ENVIRONMENT.

MODEL DISCUSSION: GEFS, ECENS, AND GOOGLE DEEPMIND ENSEMBLE SUITES
PREDICT A VARIETY OF MULTI-MODAL TRACK SOLUTIONS THAT APPEAR TO BE
LARGELY DEPENDENT UPON THE TIMING AND LOCATION OF CYCLONE GENESIS.
THE LIMITED MODEL TRACK GUIDANCE CURRENTLY AVAILABLE LEANS TOWARD A
MORE NORTHWESTWARD TRACK UNDER THE STEERING INFLUENCE OF THE STR TO
THE WEST. THE JTWC TRACK FORECAST IS PLACED NEAR THE MULTI-MODEL
CONSENSUS, ALBEIT WITH LOW CONFIDENCE CONSIDERING THE LEVEL OF
UNCERTAINTY. THERE IS BETTER AGREEMENT AMONG THE MODEL GUIDANCE FOR
INTENSITY AS SIMILAR ENVIRONMENTAL CONDITIONS SHOULD PREVAIL
REGARDLESS OF ANY VARIABILITY IN THE TRACK. HAFS-A IS BY FAR THE
MOST AGGRESSIVE MODEL, SUGGESTING A PEAK INTENSITY OF 125 KTS WHILE
THE REMAINDER OF GUIDANCE IS IN THE 90-110 KNOT RANGE. OVERALL, THE 
JTWC INTENSITY FORECAST IS PLACED NEAR THE MULTI-MODEL CONSENSUS WITH
MEDIUM CONFIDENCE. 

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