WDPN31 PGTW 012100
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: 24.2N 147.6E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 782 NM SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-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) 04W WITH DEEP CONVECTION SLIGHTLY OFFSET TO THE
NORTH OF A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC)
AND A LARGE BAND OF CONVECTION ALONG THE EASTERN PERIPHERY OF THE
SYSTEM. A 011026Z METOP-B ASCAT IMAGE REVEALED THE ASYMMETRIC
NATURE OF THE WIND FIELD WITH THE STRONGEST WINDS (25-30 KTS)
CONFINED TO THE EASTERN SEMICIRCLE. ENVIRONMENTAL ANALYSIS
INDICATES THAT 04W IS IN A MARGINALLY FAVORABLE ENVIRONMENT
CHARACTERIZED BY STRONG POLEWARD OUTFLOW ALOFT, LOW TO MODERATE
(15-20 KTS) VERTICAL WIND SHEAR, AND WARM (28-29 C) SEA SURFACE
TEMPERATURES. THE TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) CELL
THAT IS CENTERED ABOUT 300 NM TO THE SOUTHWEST OF THE SYSTEM IS
CURRENTLY HINDERING THE EQUATORWARD OUTFLOW AND IS THE MAIN CAUSE
OF THE SOUTHERLY VERTICAL WIND SHEAR. THE TUTT CELL IS ALSO
INTRODUCING A TONGUE OF DRY AIR TO THE SOUTHERN AND SOUTHWESTERN
PORTIONS OF THE CIRCULATION. THE INITIAL POSITION IS PLACED WITH
HIGH CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC IN ANIMATED EIR
IMAGERY. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON PERSISTENCE FROM THE MENTIONED ASCAT IMAGE AND
AGREEMENT WITH AGENCY DVORAK FIXES.

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

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF AN ELONGATED
SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T1.5 - 25 KTS
   CIMSS DPRINT: 35 KTS AT 011800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: PRESSURE FROM THE TUTT CELL AND SLIGHT DRY AIR
ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: TD 04W IS FORECAST TO CONTINUE ON A
NORTH-NORTHWESTERLY TRACK ALONG THE WESTERN PERIPHERY OF THE STR
THROUGH TAU 48. AFTER TAU 48, RIDGING TO THE WEST WILL BUILD AND
PULL THE VORTEX TOWARD THE NORTHEAST THROUGH THE REMAINDER OF THE
FORECAST PERIOD. REGARDING INTENSITY, 04W IS FORECAST TO STEADILY
INTENSIFY TO A PEAK INTENSITY OF 55 KTS AT TAU 72 DUE TO THE
OVERALL CONDUCIVE ENVIRONMENT. THE SYSTEM WILL CONTINUE TO DISTANCE
ITSELF FROM THE TUTT CELL, WHICH WILL ALLOW FOR IMPROVEMENTS TO THE
EQUATORWARD OUTFLOW CHANNEL AS THE SYSTEM GAINS LATITUDE. AFTER TAU
72, SEA SURFACE TEMPERATURES WILL BEGIN TO COOL, PUTTING A HALT TO
FURTHER INTENSIFICATION. AND BY TAU 120, SEA TEMPERATURES ARE
EXPECTED TO DROP TO AROUND 25 C, WHICH WILL INITIATE A WEAKENING
TREND. ADDITIONALLY, AN UPPER-LEVEL TROUGH IS FORECAST TO PROPAGATE
EASTWARD AND BEGIN INTERACTING WITH THE SYSTEM NEAR TAU 120.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGH TAU 72 WITH THE EXCEPTIONS OF NAVGEM AND GALWEM.
NAVGEM HAS A MUCH FASTER TRACK SPEED AND GALWEM HAS THE VORTEX
MAKING A SHARP EASTWARD TURN NEAR TAU 48. DISCOUNTING THE TWO
OUTLIERS, THERE IS A 100 NM CROSS-TRACK SPREAD AT TAU 72. AFTER TAU
72, GFS STARTS TO BECOME AN OUTLIER AS IT ACTUALLY HAS THE VORTEX
MAKING A TURN WESTWARD AFTER TAU 96 AS IT GETS CAUGHT UNDERNEATH
RIDGING TO THE NORTH. THE TRACK SPEED OF THE SYSTEM WILL LIKELY
DICTATE WHETHER IT WILL GET CAUGHT AND PULLED WESTWARD (SLOW) OR
MOVE OFF TO THE NORTHEAST (FAST). THE JTWC TRACK FORECAST CURRENTLY
HAS THE NORTHEASTWARD TRACK AS THAT IS WHAT THE MAJORITY OF
CONSENSUS DEPICTS. INTENSITY GUIDANCE IS IN MODERATE AGREEMENT WITH
MOST MODELS HAVING THE PEAK INTENSITY FROM 50-60 KTS AT TAU 84-96.
COAMPS-TC (GFS BASED) SUGGESTS A HIGHER PEAK OF AROUND 85 KTS.
OVERALL, THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO THE
MULTI-MODEL CONSENSUS WITH MEDIUM CONFIDENCE.

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