Advisories

WDPN31 PGTW 080300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 22W (KROVANH) 
WARNING NR 028//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 30.3N 132.6E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 224 NM SOUTHEAST OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
DEPRESSION (TD) 22W FEATURING A FULLY EXPOSED LOW-LEVEL CIRCULATION
CENTER (LLCC) AND FLARING CONVECTION IN THE NORTHWEST QUADRANT,
VENTING INTO A JET STREAK OVER THE EASTERN SEA OF JAPAN. ALTHOUGH
THE SYSTEM HAS TAKEN A NORTH-NORTHWESTWARD JOG OVER THE LAST SIX
HOURS, IT IS EMBEDDED IN DEEP-LAYER SOUTHERLY FLOW ON THE WESTERN
PERIPHERY OF A STRONG ANTICYCLONE SOUTHEAST OF HONSHU. THE
ANTICYCLONIC FLOW ASSOCIATED WITH THE UPPER-LEVEL RIDGE IS
ESPECIALLY STRONG, IMPARTING 20-25 KTS OF SOUTHERLY VERTICAL WIND
SHEAR (VWS) OVER THE SYSTEM. TD 22W IS MOVING OVER WATERS OF 28-29
DEGREES CELSIUS, BUT THE COMBINATION OF MODERATE TO HIGH VWS AND
SUBSTANTIAL DRY AIR INTRUSION INTO THE CIRCULATION RESULTS IN A
LARGELY UNFAVORABLE ENVIRONMENT FOR TROPICAL DEVELOPMENT. DESPITE
THESE FACTORS, TD 22W HAS NOT APPRECIABLY WEAKENED, AS EVIDENCED BY
A TIMELY 072359Z BULLS-EYE ASCAT-B PASS INDICATING WINDS OF UP TO
30 KTS IN THE SOUTHEAST QUADRANT, CONSISTENT WITH THE 071158Z
ASCAT-C DATA. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE
BASED ON THE WELL-DEFINED LLCC IN THE MSI. THE INITIAL INTENSITY IS
HELD AT 30 KTS WITH HIGH CONFIDENCE BASED ON THE RECENT
SCATTEROMETER DATA.

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: T1.5 - 25 KTS
   KNES: T1.5 - 25 KTS
   CIMSS SATCON: 45 KTS AT 071940Z
   CIMSS ADT: 41 KTS AT 072330Z
   CIMSS AIDT: 40 KTS AT 072330Z
   CIMSS D-MINT: 31 KTS AT 072012Z
   CIMSS D-PRINT: 29 KTS AT 072330Z

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: 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 WILL CONTINUE POLEWARD ALONG THE
WESTERN FLANK OF THE STR SOUTHEAST OF HONSHU THROUGH TAU 12. BY TAU
24, THE SYSTEM WILL ROUND THE NORTHWESTERN PERIPHERY OF THE RIDGE
AND TURN NORTHEASTWARD AS IT INTERACTS WITH A STATIONARY FRONT NEAR
THE SOUTHERN COAST OF HONSHU. THIS MOTION WILL CONTINUE UNTIL
DISSIPATION BY TAU 36. WHILE TD 22W WILL TRACK OVER SUFFICIENTLY
WARM WATERS PRIOR TO LANDFALL, PERSISTENT VWS AND DRY AIR INTRUSION
WILL MAINTAIN AN UNFAVORABLE ENVIRONMENT FOR TROPICAL DEVELOPMENT.
THESE FACTORS WOULD NORMALLY LEAD TO WEAKENING. HOWEVER, AS TD 22W
CONTINUES TO GAIN LATITUDE, THE EXTENSIVE ANTICYCLONE SOUTHEAST OF
HONSHU WILL SHIFT WESTWARD, TIGHTENING THE SURFACE PRESSURE
GRADIENT BETWEEN THE SYSTEM AND THE RIDGE AND ENHANCING LOW-LEVEL
WINDS, PARTICULARLY OVER THE EASTERN PORTION OF THE CIRCULATION.
CONCURRENTLY, THE SOUTHEASTERN COASTLINE OF KYUSHU MAY ENHANCE THE
COAST-PARALLEL FLOW, SUPPORTING A LOCALIZED COASTAL JET OVER THE
WESTERN PORTION OF THE LLCC. THESE EFFECTS WILL SUPPORT A 30-KT
INTENSITY THROUGH TAU 12. AFTER LANDFALL, TERRAIN INTERACTION OVER
HONSHU WILL PROMOTE STEADY WEAKENING THROUGH DISSIPATION BY TAU 36.
THEREFORE, THE JTWC INTENSITY FORECAST MAINTAINS 30 KTS THROUGH TAU
12 AND THEN WEAKENS THE SYSTEM TO DISSIPATION BY TAU 36. DESPITE
THE WEAKENING TREND, LOCALIZED TERRAIN-ENHANCED WIND SPEEDS MAY
OCCUR IN FAVORED COASTAL GAPS, INCLUDING THE KII CHANNEL AND WAKASA
BAY.

MODEL DISCUSSION: IN PRIOR MODEL RUNS, SEVERAL DYNAMICAL MODELS
DEPICTED A SCENARIO IN WHICH TD 22W WOULD MAKE LANDFALL OVER
WESTERN SHIKOKU AND BECOME QUASI-STATIONARY IN A WEAKER STEERING
ENVIRONMENT, LEADING TO DISSIPATION. IN THE CURRENT GUIDANCE SUITE,
MOST TRACKERS TURN THE SYSTEM EASTWARD AFTER TAU 12, WHILE GFS,
HAFS-A, AND HWRF MAINTAIN MORE INLAND SOLUTIONS. THE AI MODELS
REMAIN THE FARTHEST EAST, DEPICTING A STRONGER EASTWARD TURN THAT
KEEPS THE CIRCULATION TRACKING NEARLY PARALLEL TO THE MOUNTAIN
RANGES OF HONSHU. THESE DIFFERENCES RESULT IN A LARGE ALONG-TRACK
SPREAD OF 370 NM AT TAU 36. THE JTWC FORECAST TRACK LIES NEAR THE
CONSENSUS THROUGH TAU 12 AND THEN FOLLOWS A BLEND OF THE AI MODELS
AND THE CONSENSUS. THERE REMAINS SOME SPREAD IN THE INTENSITY AIDS,
WITH HAFS-A AND COAMPS-TC DEPICTING A SLIGHT INTENSIFICATION TO 35
KTS. THE JTWC INTENSITY FORECAST FOLLOWS THE WEAKENING TREND
DEPICTED BY THE LOWER-END EXPERIMENTAL GOOGLE DEEPMIND SOLUTION,
GIVEN THE PREDICTED EFFECTS OF PERSISTENT SHEAR, DRY AIR, AND LAND
INTERACTION.

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