Advisories

WDPN31 PGTW 072100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 22W (KROVANH) 
WARNING NR 027//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.1N 133.0E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 294 NM SOUTHEAST OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
DEPRESSION (TD) 22W WITH A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION
CENTER (LLCC) AND MEAGER CONVECTION DISPLACED TO THE NORTHWEST,
VENTING POLEWARD INTO A JET STREAK OVER THE SEA OF JAPAN. TD 22W IS
FULLY EMBEDDED IN DEEP-LAYER SOUTHERLY FLOW ASSOCIATED WITH THE
WESTERN FLANK OF A LARGE STR POSITIONED SOUTHEAST OF HONSHU. THIS
RIDGE IS PARTICULARLY STRONG ALOFT, IMPARTING 20-25 KTS OF
SOUTHERLY VERTICAL WIND SHEAR (VWS) OVER THE SYSTEM. THE
ENVIRONMENT IS UNFAVORABLE FOR DEVELOPMENT, WITH WARM SEA SURFACE
TEMPERATURES (SST) OFFSET BY MODERATE TO HIGH VWS AND DRY AIR
WRAPPING INTO THE CIRCULATION. THE SATELLITE PRESENTATION HAS
CHANGED LITTLE SINCE THE 071158Z ASCAT-C PASS, WHICH MEASURED UP TO
30 KT WINDS ALONG THE WESTERN AND EASTERN PORTIONS OF THE
CIRCULATION. THEREFORE, THE INITIAL INTENSITY IS HELD AT 30 KTS
WITH HIGH CONFIDENCE, SUPPORTED BY THE RJTD T2.0 DVORAK ESTIMATE.
THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE DUE TO THE
LLCC BEING PARTIALLY OBSCURED BY MID- TO HIGH-LEVEL CLOUDS.

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

CURRENT STEERING MECHANISM: WESTERN FLANK OF THE SUBTROPICAL RIDGE
(STR) POSITIONED SOUTHEAST OF HONSHU

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T1.5 - 25 KTS
   KNES: T1.5 - 25 KTS
   CIMSS SATCON: 45 KTS AT 071702Z
   CIMSS ADT: 49 KTS AT 071740Z
   CIMSS AIDT: 44 KTS AT 071740Z
   CIMSS D-MINT: 30 KTS AT 071704Z
   CIMSS D-PRINT: 38 KTS AT 071740Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   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 WILL CONTINUE POLEWARD ALONG THE
WESTERN FLANK OF A LARGE STR POSITIONED SOUTHEAST OF HONSHU THROUGH
TAU 12. FROM TAU 12 TO TAU 24, THE SHALLOW SYSTEM WILL ROUND THE
RIDGE AXIS AND TURN EASTWARD AS IT INTERACTS WITH A STATIONARY
FRONT DRAPED OVER HONSHU. TD 22W WILL THEN MAINTAIN THIS
EAST-NORTHEASTWARD TRAJECTORY UNTIL DISSIPATION. THE ENVIRONMENT
WILL REMAIN UNFAVORABLE THROUGH THE FORECAST PERIOD. ALTHOUGH THE
VORTEX WILL REMAIN OVER WARM WATERS OF 28-29 DEGREES CELSIUS
THROUGH TAU 24, PERSISTENT VWS AND ADDITIONAL DRY AIR ADVECTION
ASSOCIATED WITH THE STR WILL LIMIT DEVELOPMENT. THESE CONDITIONS
WOULD NORMALLY SUPPORT WEAKENING. HOWEVER, AS TD 22W TRAVELS
POLEWARD, A TIGHTENING SURFACE PRESSURE GRADIENT BETWEEN THE SYSTEM
AND THE STR TO THE EAST WILL ENHANCE LOW-LEVEL WINDS, PARTICULARLY
OVER THE EASTERN PORTION OF THE CIRCULATION. SEPARATELY, THE
SOUTHEASTERN COASTLINE OF KYUSHU MAY ENHANCE LOW-LEVEL,
COAST-PARALLEL FLOW, SUPPORTING A COASTAL JET OVER THE WESTERN
SEMICIRCLE OF THE LLCC. THE FORECAST DEPICTS A STEADY INTENSITY
TREND THROUGH TAU 24. HOWEVER, MARGINAL INTENSIFICATION TO 35 KTS
IS POSSIBLE IF THE PRESSURE GRADIENT AND COASTAL JET EFFECTS BECOME
MORE PRONOUNCED. THE SYSTEM WILL WEAKEN AFTER LANDFALL, WITH
DISSIPATION PREDICTED BY TAU 48.

MODEL DISCUSSION: THE JTWC FORECAST TRACK REFLECTS THE OVERALL
PATTERN OF THE TRACK GUIDANCE. MODEL DISAGREEMENT INCREASES
SUBSTANTIALLY AFTER TAU 24, WITH A VERY LARGE ALONG-TRACK SPREAD OF
NEARLY 600 NM BY TAU 48. THE DYNAMICAL MODELS TAKE THE SYSTEM
INLAND OVER HONSHU, WHILE THE AI MODELS TURN THE CIRCULATION
EASTWARD AND KEEP IT NEAR THE COAST. THIS DIVERGENCE CAN BE
ATTRIBUTED TO DIFFERENCES IN THE STRENGTH AND POSITION OF THE STR.
A STRONGER RIDGE THAT MIGRATES WESTWARD WOULD FAVOR A MORE INLAND
TRACK. IN CONTRAST, THE AI MODELS MAINTAIN A MORE EASTWARD TRACK
NEARLY PARALLEL TO THE MOUNTAIN RANGES OF HONSHU. THE JTWC FORECAST
TRACK IS PLACED NEAR THE CONSENSUS THROUGH TAU 24 AND THEN HEDGES
TOWARD THE AI-MODEL SOLUTIONS AT TAU 36 AND TAU 48. SEVERAL
INTENSITY AIDS SHOW SLIGHT INTENSIFICATION TO 35 KTS DURING THE
NEXT 24 HOURS. THE JTWC INTENSITY FORECAST IS ALIGNED MOST CLOSELY
WITH THE EXPERIMENTAL GOOGLE DEEPMIND GUIDANCE THROUGH TAU 48,
WHICH IS ON THE LOWER END OF THE GUIDANCE ENVELOPE.

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