Tropical Storm TALAS Advisory Mi, 21.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 17W (SEVENTEEN)
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 25.4N 138.9E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 595 NM SOUTH OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A LARGE
CLUSTER OF DEEP PERSISTENT CONVECTION OVER THE NORTHERN SEMICIRCLE
OBSCURING A LOW LEVEL CIRCULATION CENTER (LLCC). AN EARLIER 211632Z
GMI 89GHZ MICROWAVE IMAGE REVEALS SHALLOW BANDING WRAPPING INTO A
LOW LEVEL CIRCULATION CENTER POSITIONED ALONG THE SOUTHWESTERN EDGE
OF A CURVED CONVECTIVE BAND. THE INITIAL POSITION IS PLACED WITH
MEDIUM CONFIDENCE BASED ON EIR IMAGERY AND GMI MICROWAVE IMAGERY.
THE INITIAL INTENSITY OF 25 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE IMPROVING CONVECTIVE STRUCTURE AS WELL AS A
COMBINATION OF AGENCY DVORAK INTENSITY ESTIMATES, PGTW T1.0, RJTD
T1.0, AND KNES T2.0.
INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).
CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T1.0 - 25 KTS
   RJTD: T1.0 - 25 KTS
   KNES: T2.0 - 30 KTS
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 0-5 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.
FORECAST DISCUSSION: TD 17W IS FORECAST TO TRACK POLEWARD ALONG THE
WESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) BEFORE
MAKING LANDFALL INTO HONSHU. ENVIRONMENTAL CONDITIONS OVER THE NEXT 36
HOURS ARE CHARACTERIZED BY WARM SEA SURFACE TEMPERATURES (SSTS) (28-
29C), LOW VERTICAL WIND SHEAR (VWS) (0-5 KNOTS) AND MODERATE POLEWARD
OUTFLOW INDUCED BY AN UPPER LEVEL TROUGH SITUATED TO THE SOUTHWEST OF
17W INCREASING THE POLEWARD OUTFLOW, OFFSET BY DRY AIR ENTRAINMENT.
LEADING TO AN OVERALL MARGINALLY FAVORABLE ENVIRONMENT FOR DEVELOPMENT
WHICH WILL ALLOW 17W TO REACH A POTENTIAL MAXIMUM INTENSITY OF 45
KNOTS BY TAU 36. BETWEEN TAU 36 AND TAU 48 THE SYSTEM IS FORECAST TO
TURN AND TRACK TO THE NORTHEAST AS 17W ROUNDS THE SUBTROPICAL RIDGE
AXIS. ADDITIONALLY, A SHORTWAVE TROUGH WITH MODERATE TEMPERATURE
ADVECTION AND POTENTIAL VORTICITY ADVECTION (PVA) TO THE NORTHWEST OF
THE SYSTEM WILL BEGIN TO BREAK DOWN THE STR TO THE WEST WHILE
INCREASING VWS. BY TAU 48, 17W WILL CONTINUE TO WEAKEN AS DECAY SHIPS
(DSHA) GUIDANCE INDICATES THE SYSTEM WILL MOVE OVER COOLER SSTS BEFORE
MAKING LANDFALL INTO HONSHU. BETWEEN TAU 48 AND TAU 72, LAND
INTERACTION WILL SIGNIFICANTLY IMPACT INTENSITY AS THE SYSTEM
CONTINUES TO TRACK TO THE NORTHEAST BEFORE DISSIPATING.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT
WITH THE EXCEPTION OF THE UKMET TRACKER (EGRI), WHICH IS THE
WESTERN OUTLIER, THROUGH TAU 48 WITH ONLY A 55NM SPREAD IN THE
SOLUTIONS. BETWEEN TAU 48 AND TAU 72 THE GUIDANCE BEGINS TO SPREAD
AS UNCERTAINTY INCREASES IN BOTH CROSS TRACK AND ALONG TRACK
VARIABILITY. THIS IS POSSIBLY DUE TO HOW MODELS ARE HANDLING THE
LAND INTERACTION AND SHORTWAVE TROUGH INTERACTION DIFFERENTLY.
THEREFORE, THE JTWC OFFICIAL TRACK FORECAST IS PLACED WITH MEDIUM
CONFIDENCE AND REMAINS CLOSE TO CONSENSUS MODEL TRACK GUIDANCE
THROUGH TAU 72. RELIABLE INTENSITY GUIDANCE SHOWS MODERATE SPREAD
WITH HWRF SHOWING A HIGH END SOLUTION UP TO 55 KNOTS BY TAU 36,
WHILE DECAY SHIPS (DSHA) GUIDANCE INDICATES A MORE CONSERVATIVE 35
KNOT MAXIMUM INTENSITY BY TAU 36. AFTER TAU 48, LAND INTERACTION
AND EVENTUAL LANDFALL OCCURS ALL GUIDANCE SHOWS A SHARP DECREASE IN
INTENSITY. THUS THE JTWC INTENSITY FORECAST IS PLACED WITH LOW
CONFIDENCE GIVEN THE HIGH UNCERTAINTY DUE TO THE BULK OF THE
GUIDANCE DISAGREEING ON THE EXTENT OF THE PEAK INTENSITY.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: LOW//
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