Advisories

WDPN31 PGTW 082100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 22W (KROVANH) 
WARNING NR 031//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 33.1N 133.5E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 100 NM SOUTHEAST OF IWAKUNI, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 13 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 WELL-DEFINED, FULLY EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC), DEEP CONVECTION SHEARED TO THE
NORTHWESTERN PERIPHERY, AND OUTFLOW ALOFT VENTING POLEWARD INTO A
JET STREAM OVER THE SEA OF JAPAN AND NORTHERN HONSHU. THE
ENVIRONMENT REMAINS UNFAVORABLE DUE TO A STRONG UPPER-LEVEL RIDGE
TO THE EAST, IMPARTING 20-25 KTS OF SOUTHERLY VERTICAL WIND SHEAR
(VWS) ALONG WITH DRY AIR ENTRAINMENT INTO THE SYSTEM'S CORE.
DESPITE THESE INHIBITING FACTORS, THE SYSTEM BRIEFLY ACHIEVED
TROPICAL STORM STRENGTH OF 35 KTS NEAR 081200Z BUT HAS SINCE
WEAKENED TO TD INTENSITY. AS TD 22W TRACKED POLEWARD IN THE PAST 12
HOURS, IT INTERACTED WITH THE EASTERN COASTLINE OF KYUSHU.
EQUATORWARD LOW-LEVEL FLOW WAS CHANNELED THROUGH THE BUNGO CHANNEL
INTO THE WESTERN SEMICIRCLE OF THE CIRCULATION, WHERE IT
ACCELERATED PARALLEL TO KYUSHU'S COASTLINE. THIS LOCALIZED TERRAIN
EFFECT BRIEFLY ENHANCED SURFACE WIND SPEEDS IN THE WESTERN
SEMICIRCLE, EVIDENCED BY THE 081115Z ASCAT-B PASS DEPICTING A SWATH
OF 30-35 KT WINDS WEST OF THE SYSTEM CENTER AND FURTHER SUPPORTED
BY SHIP OBSERVATIONS. TD 22W IS NOW TURNING NORTHEASTWARD AND
MOVING AWAY FROM KYUSHU, WITH A PORTION OF THE CIRCULATION MOVING
OVER SHIKOKU AND THE DEEP CONVECTION BECOMING LESS VIGOROUS SINCE
081200Z. IN FACT, A 081508Z OSCAT-3 IMAGE REVEALED WIND SPEEDS OF
UP TO 30 KTS NEAR THE BUNGO CHANNEL EXIT, AND SURFACE OBSERVATIONS
AT CAPE MUROTO REPORTED 1-MINUTE EQUIVALENT WIND SPEEDS NEAR 30
KTS. THEREFORE, THE INITIAL INTENSITY IS SET AT 30 KTS WITH HIGH
CONFIDENCE, SUPPORTED BY THE T2.0 CLASSIFICATION FROM PGTW AND THE
MAJORITY OF THE OBJECTIVE ESTIMATES FROM CIMSS. THE INITIAL
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC
IN ANIMATED SHORTWAVE-INFRARED (SWIR) IMAGERY.

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

CURRENT STEERING MECHANISM: MID-LATITUDE WESTERLIES ALONG THE
NORTHWESTERN FLANK OF A SUBTROPICAL RIDGE (STR) POSITIONED
SOUTHEAST OF HONSHU

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.0 - 25 KTS
   CIMSS SATCON: 38 KTS AT 081800Z
   CIMSS ADT: 29 KTS AT 081800Z
   CIMSS AIDT: 34 KTS AT 081800Z
   CIMSS D-MINT: 31 KTS AT 081729Z
   CIMSS D-PRINT: 31 KTS AT 081800Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 IS BEGINNING TO TURN EAST-NORTHEASTWARD
AS IT ROUNDS THE NORTHWESTERN FLANK OF THE LOW- TO MID-LEVEL STR
SOUTHEAST OF HONSHU. THE MID-LATITUDE WESTERLIES WILL BECOME THE
PRIMARY STEERING MECHANISM, DRIVING THE SYSTEM NEARLY PARALLEL TO
THE MOUNTAIN RANGES OF CENTRAL HONSHU THROUGH TAU 24. ATMOSPHERIC
CONDITIONS WILL BE HOSTILE FOR THE FORESEEABLE FUTURE WITH VWS
INCREASING TO 30-40 KTS AND DRY AIR STREAMING IN FROM THE SOUTH.
FURTHERMORE, THE SHALLOW VORTEX WILL BEGIN TO INTERACT WITH A
STATIONARY FRONT DRAPED OVER HONSHU. THESE FACTORS, COMBINED WITH
INTERACTION WITH THE RUGGED TERRAIN OF MAINLAND JAPAN, WILL LEAD TO
RAPID DISSIPATION OF THE CIRCULATION AS IT BECOMES ABSORBED INTO
THE FRONTAL BOUNDARY. THE CIRCULATION MAY BECOME ILL-DEFINED PRIOR
TO TAU 24. REGARDLESS, THE REMNANTS OF TD 22W MAY LEAD TO LOCALIZED
TERRAIN-INDUCED WIND ENHANCEMENTS IN CHANNELS AND COASTAL AREAS,
SUCH AS THE MOUTH OF THE KII CHANNEL AND OFFSHORE OF THE IZU
PENINSULA.

MODEL DISCUSSION: MODELS AGREE ON A NORTHEAST TO EAST-NORTHEAST
TRAJECTORY THROUGH TAU 24. BOTH THE DYNAMICAL AND AI MODELS ARE
CLUSTERED TOGETHER WITHIN THE CORE GUIDANCE ENVELOPE, LEADING TO
HIGH CONFIDENCE IN THE JTWC FORECAST TRACK. THE FORECAST TRACK IS
SET NEAR THE CONSENSUS AT TAU 12 AND NEAR A BLEND OF THE AI MODELS
AND THE CONSENSUS AT TAU 24. THE INTENSITY GUIDANCE UNIVERSALLY
INDICATES A WEAKENING TREND FROM TAU 12 TO TAU 24. THE JTWC
INTENSITY FORECAST IS ALIGNED WITH THE SOLUTIONS FROM THE HAFS-A
AND THE EXPERIMENTAL GOOGLE DEEPMIND MODELS, SHOWING DISSIPATION BY
TAU 24. THIS INTENSITY FORECAST LIES ON THE LOWER END OF THE
GUIDANCE ENVELOPE.

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