Advisories

WDPN31 PGTW 070900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 22W (KROVANH) 
WARNING NR 025//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.1N 132.6E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 260 NM EAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: 
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL 
DEPRESSION 22W (KROVANH) WITH A MOSTLY EXPOSED LOW-LEVEL CIRCULATION 
CENTER (LLCC) THAT HAS BECOME MORE WELL-DEFINED OVER THE PAST 6 HOURS. 
CONVECTIVE ACTIVITY HAS PERSISTED WITHIN THE NORTHWESTERN QUADRANT AND 
CORRESPONDING CLOUD TOPS MEASURING COLDER THAN -80 C IN SOME AREAS. 
THE CONVECTION IS CLEARLY SHEARED TO THE NORTHWEST, WHICH IS CAUSED BY 
MODERATE TO HIGH SOUTHEASTERLY SHEAR ACTING ON THE SYSTEM. THE INITIAL 
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE ANIMATED MSI. THE 
INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED 
ON THE AGENCY DVORAK FIXES AND CIMSS INTENSITY ESTIMATES LISTED BELOW. 
ENVIRONMENTAL ANALYSIS INDICATES THAT 22W IS IN A MARGINAL ENVIRONMENT 
CHARACTERIZED BY MODERATE POLEWARD OUTFLOW ALOFT, 20-25 KTS 
SOUTHEASTERLY VERTICAL WIND SHEAR, DRY AIR ENTRAINMENT, AND WARM (28-
29 C) SEA SURFACE TEMPERATURES.

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

CURRENT STEERING MECHANISM: THE WESTERN FLANK OF A SUBTROPICAL RIDGE 
(STR) CENTERED SOUTHEAST OF JAPAN

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RCTP: T1.5 - 25 KTS
   KNES: T1.5 - 25 KTS
   CIMSS ADT: 37 KTS AT 070540Z
   CIMSS AIDT: 29 KTS AT 070540Z
   CIMSS D-MINT: 32 KTS AT 070453Z
   CIMSS D-PRINT: 28 KTS AT 070540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE 
FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TD 22W HAS STARTED TO TRACK MORE NORTHWARD OVER 
THE PAST 6 HOURS AS THE SYSTEM BEGINS TO TRACK ALONG THE WESTERN 
PERIPHERY OF THE SUBTROPICAL RIDGE CENTERED TO THE SOUTHEAST OF JAPAN. 
THE TRAJECTORY IS FORECAST TO BE NEARLY DUE NORTH THROUGH TAU 24. 
FOLLOWING TAU 24, 22W WILL BEGIN TO TURN NORTHEASTWARD AS IT ROUNDS 
THE STEERING RIDGE AXIS AND APPROACHES SOUTHERN JAPAN. 22W IS THEN 
EXPECTED TO SKIRT THE COAST OF THE SHIKOKU AND KANSAI REGIONS AFTER 
TAU 36 AS IT ACCELERATES NORTHEASTWARD. IN TERMS OF INTENSITY, 22W IS 
FORECAST TO MAINTAIN ITS CURRENT INTENSITY OF 30 KTS THROUGH TAU 36 
UNDER THE EFFECTS OF THE MARGINAL ENVIRONMENT. DRY AIR ENTRAINMENT AND 
SOUTHERLY SHEAR IS EXPECTED TO WORSEN THROUGH THIS TIME; HOWEVER, THE 
POLEWARD OUTFLOW CHANNEL WILL IMPROVE. AFTER TAU 36, SOUTHWESTERLY 
SHEAR WILL SIGNIFICANTLY INCREASE, CAUSING 22W TO WEAKEN JUST BEFORE
MAKING LANDFALL IN JAPAN. THE SHALLOW VORTEX WILL THEN RAPIDLY ERODE 
AND STRETCH OVER THE MOUNTAINOUS TERRAIN WITH DISSIPATION FORECAST TO 
OCCUR AROUND TAU 48, SOUTH OF KYOTO.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS NOW IN GOOD AGREEMENT 
THROUGH TAU 36 WITH A CROSS-TRACK SPREAD MEASURED TO BE ABOUT 50 NM. 
AFTER TAU 36, ALONG-TRACK SPREAD SHARPLY INCREASES DUE TO VARYING 
TRACK SPEEDS AROUND THE RIDGE AXIS BETWEEN MODELS. THE EC-AIFS AND THE 
EXPERIMENTAL GOOGLE DEEPMIND ENSEMBLE MEAN ARE AMONG THE FASTEST 
TRACKERS, WHILE THE ECMWF AND ECMWF ENSEMBLE MEAN ARE MUCH SLOWER. AT 
TAU 48 THE ALONG-TRACK SPREAD IS MEASURED TO BE 130 NM, CAUSING THERE 
TO BE SOME UNCERTAINTY IN TRACK SPEEDS FOLLOWING THE NORTHEASTWARD 
TURN. THE JTWC TRACK FORECAST IS PLACED NEAR THE MULTI-MODEL CONSENSUS 
THROUGH TAU 36 AND THEN CLOSER TO THE GOOGLE DEEPMIND THROUGH TAU 48. 
INTENSITY GUIDANCE GENERALLY AGREES ON A STEADY INTENSITY THROUGH TAU 
36 FOLLOWED BY WEAKENING WITH NO NOTABLE OUTLIERS PRESENT. THE JTWC 
INTENSITY FORECAST IS PLACED NEAR THE CONSENSUS THROUGH TAU 36 AND 
THEN SLIGHTLY LOWER THROUGH TAU 48 DUE TO THE EXPECTED RAPID WEAKENING 
OVER JAPAN.

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