Tropical Storm TALAS Advisory Do, 22.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 17W (SEVENTEEN)
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 26.0N 137.7E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 567 NM SOUTH OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC), WITH DEEP PERSISTENT
CONVECTION DISPLACED TO THE NORTHWEST QUADRANT. AN EARLIER 212135Z
SSMIS 91GHZ 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 MSI IMAGERY AND THE SSMIS MICROWAVE
IMAGERY. THE INITIAL INTENSITY OF 25 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE CURRENT 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: T1.5 - 25 KTS
   RJTD: T1.0 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 26 KTS AT 212040Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: ENVIRONMENTAL CONDITIONS ARE MARGINALLY
FAVORABLE CHARACTERIZED BY WARM SEA SURFACE TEMPERATURES (SSTS)
(28-29C), AND MODERATE POLEWARD OUTFLOW INDUCED BY AN UPPER LEVEL
TROUGH SITUATED TO THE SOUTHWEST OF 17W. HOWEVER, THESE FAVORABLE
ENVIRONMENTAL FACTORS ARE OFFSET BY MODERATE VERTICAL WIND SHEAR
(VWS) (10-15 KNOTS) BASED ON DECAY SHIPS (DSHA) GUIDANCE, ALONG WITH
GFS MODELED LOW 700MB-300MB RELATIVE HUMIDITY VALUES AROUND THE
SOUTHERN PERIPHERY OF THE SYSTEM. TD 17W IS FORECAST TO TRACK POLEWARD
ALONG THE WESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR)
BEFORE MAKING LANDFALL INTO HONSHU. BASED ON THE OVERALL MARGINALLY
FAVORABLE ENVIRONMENT, 17W WILL STRUGGLE TO INTENSIFY FOR THE FIRST 12
HOURS, HOWEVER AS 17W REACHES THE STR AXIS AND BECOMES POSITIONED
POLEWARD OF THE UPPER LEVEL TROUGH, VWS MAY LESSEN ENOUGH TO PROVIDE A
BRIEF WINDOW OF OPPORTUNITY FOR THE SYSTEM TO BECOME BETTER
CONSOLIDATED THUS STRENGTHEN BETWEEN TAU 24 AND TAU 36. THEREFORE, THE
JTWC FORECAST CALLS FOR 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 DUE TO LAND
INTERACTION AFTER 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 OVERALL TIGHT
AGREEMENT WITH THE EXCEPTION OF JGSM, 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 CLOSE TO 50 KNOTS BY TAU 36, WHILE DECAY SHIPS
(DSHA) GUIDANCE INDICATES A LOWER INTENSITY SOLUTION OF 30
KNOTS 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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