WDPN31 PGTW 060300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 15W (FIFTEEN) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.4N 157.6E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 318 NM NORTHEAST OF MINAMI TORI SHIMA
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
A 052228Z ASCAT 25KM RESOLUTION PASS AND THE JTWC DVORAK CONFIRM
THAT INVEST 97W REACHED TROPICAL DEPRESSION STRENGTH AND IS NOW
TROPICAL DEPRESSION (TD) 15W. BOTH TOOLS CONFIRM A SYSTEM INTENSITY
OF 25 KNOTS. THE LOW-LEVEL CIRCULATION (LLCC) IS UNBALANCED, WITH
THE STRONGEST WINDS SURGING OVER THE SOUTHEASTERN QUADRANT. THERE
IS A SHARP CONTRAST OVER THE LLCC WITH DRY AIR OVER THE POLEWARD
SEMICIRCLE AND DEEP CONVECTION OVER THE EQUATORWARD SIDE. ANIMATED
VISUAL IMAGERY DURING THE PAST TWELVE HOURS INDICATES THE LLCC IS
TUCKING UNDER THE CONVECTION. THE SYSTEM IS BEING FORCED ALMOST
DIRECTLY POLEWARD IN A BREAK IN THE SUBTROPICAL RIDGE, FOLLOWING
THE WESTERN FLANK OF THE SEASONAL SUBTROPICAL HIGH THAT IS ANCHORED
IN THE EASTERN PACIFIC. THERE IS A DEARTH OF DEEP MOISTURE AND MUCH
HIGHER VERTICAL WINDSHEAR JUST POLEWARD OF THE SYSTEM, LIMITING
DEVELOPMENT.

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

CURRENT STEERING MECHANISM: TD 15W IS STEERING THROUGH A BREAK IN
THE SUBTROPICAL RIDGE BETWEEN THE 150TH AND 160TH LATITUDES. THE
BREAK IS BETWEEN THE TWO SEASONAL ANTICYCLONES CENTERED OVER THE
EASTERN PACIFIC AND THE BONIN ISLANDS.  

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.0 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS D-MINT: 31 KTS AT 052248Z
   CIMSS D-PRINT: 29 KTS AT 060000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK EQUATORWARD
   OTHER FACTORS: LACK OF DEEP MOISTURE ON THE POLEWARD SIDE OF THE
SYSTEM.

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: TROPICAL DEPRESSION 15W HAS NOWHERE TO GO BUT
DIRECTLY POLEWARD INTO AN INCREASINGLY HOSTILE ENVIRONMENT. TREND
AND MOMENTUM PLUS STATISTICAL-DYNAMICAL GUIDANCE INDICATE THE
SYSTEM MAY INTENSIFY SLIGHTLY UP TO LOW GALE FORCE BUT THE HIGH
VERTICAL WINDSHEAR AND DRY AIR ENTRAINMENT WILL LIMIT DEVELOPMENT
AND CAUSE THE SYSTEM TO WEAKEN BEFORE IT MERGES WITH THE POLAR
FRONT. THE SYSTEM WILL PEAK IN INTENSITY NEAR THE 33RD LATITUDE AS
IT ROUNDS THE AXIS OF THE SUBTROPICAL RIDGE, AND BY TAU 72 THE
SYSTEM WILL LIKELY BE FULLY FILLED AND UNFINDABLE. THE POLAR FRONT
IS CURRENTLY BEGINNING A SHIFT POLEWARD AS THE PATTERN AMPLIFIES
DUE TO A MAJOR SHORT WAVE DIGGING INTO JAPAN, CAUSING A HIGH
AMPLITUDE RIDGE TO FORM ALONG THE DATELINE. THE INCREASING
MERIDIONAL FLOW WILL CAUSE FURTHER SEPARATION BETWEEN TD 15W AND
POLAR FRONT, RESULTING IN A DISSIPATION OVER WATER SCENARIO RATHER
THAN EXTRA-TROPICAL TRANSITION. 

MODEL DISCUSSION: THE ECMWF ENSEMBLE LIES WEST OF A VERY TIGHT PACK
OF TRACK GUIDANCE, HENCE THE JTWC FORECAST HEDGES SLIGHTLY WEST OF
THE MULTI-MODEL CONSENSUS. INTENSITY GUIDANCE IS GOOD IN SHOWING A
SLIGHT UPWARD TREND OVER THE FIRST 24 HOURS. THE JTWC INTENSITY IS
BASED HEAVILY IN THE GFS-BASED SHIPS STATISTICAL DYNAMICAL GUIDANCE
IN THE EARLY STAGES, BUT THEN DEVIATES TO DECAY THE SYSTEM FASTER
THAN THE SHIPS GUIDANCE DUE TO THE HARSH UPSTREAM ENVIRONMENT. 

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