Tropical Storm KROSA Advisory 8月8日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (KROSA) WARNING NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 11W (KROSA), LOCATED APPROXIMATELY 182 NM SOUTH OF
IWO TO, HAS TRACKED NORTH-NORTHWESTWARD AT 04 KNOTS (KTS) OVER THE
PAST SIX HOURS. THERE IS HIGH CONFIDENCE IN THE INITIAL POSITION
BASED ON AN INTERMITTENT, DEVELOPING EYE FEATURE IN ANIMATED
ENHANCED INFRARED (EIR) SATELLITE IMAGERY. OF NOTE, THERE IS A LARGE
AREA OF CONVECTION ROTATING AROUND AND, PERIODICALLY, ALMOST
ENCAPSULATING THE CENTER. THE INITIAL INTENSITY OF 70 KTS FALLS
BETWEEN MUTLI-AGENCY DVORAK FIXES OF T4.0-T4.5 (65-77 KTS). WARM (29-
30C) SEA SURFACE TEMPERATURE, GOOD EQUATORWARD AND POLEWARD OUTFLOW
CHANNELS, AND LIGHT (10-15 KT) VERTICAL WIND SHEAR MAKE THE
ENVIRONMENT FAVORABLE FOR INTENSIFICATION. WITH OTHERWISE VERY
FAVORABLE ENVIRONMENTAL FACTORS, AN INDUCED TROUGH TO THE NORTH IS
CAUSING SUBSIDENCE AHEAD OF THE CYCLONE THAT IS LIKELY INHIBITING
MORE RAPID INTENSIFICATION. TY 11W IS TRACKING SLOWLY ALONG THE
PERIPHERY OF SUBTROPICAL RIDGING STRETCHING AROUND TO THE NORTH,
EAST, AND SOUTH.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. THROUGH TAU 72, TY 11W IS EXPECTED TO MEANDER ON A REVERSE S
PATTERN UNDER THE COMPLEX STEERING ENVIRONMENT. THIS TRACK WILL KEEP
THE SYSTEM NEAR IWO TO FOR THE DURATION OF THIS PORTION OF THE
FORECAST. BY TAU 72, THE SUBTROPICAL RIDGE (STR) WILL REORIENT
SUFFICIENTLY TO ALLOW THE SYSTEM TO MOVE NORTHWARD AT AROUND 7 KTS.
THE OVERALL FAVORABLE ENVIRONMENT WILL ALLOW SLOW INTENSIFICATION TO
85 KTS BY TAU 48. AFTER TAU 48, HIGH VWS IS EXPECTED TO CAUSE SOME
WEAKENING BY TAU 72. NUMERICAL MODEL GUIDANCE IS IN GOOD OVERALL
AGREEMENT REGARDING THE TRACK SCENARIO, HOWEVER, A BIFURCATION
BECOMES EVIDENT AROUND TAU 48 WITH NAVGEM, GFS, JGSM, AND THE GFS
ENSEMBLE MEAN MAKING A WIDER TURN TO THE EAST THAN ECMWF, UKMET,
GALWEM, AND THE ECMWF ENSEMBLE MEAN. THE CURRENT TRACK FORECAST IS
PLACED CLOSE TO CONSENSUS WITH POOR CONFIDENCE DUE TO THE
BIFURCATION.
   C. MODEL GUIDANCE CONTINUES TO DIVERGE IN THE EXTENDED FORECAST
PERIOD, WITH A GROUPING CONSISTING OF THE GFS, NAVGEM AND JGSM
MODELS DEPICTING A NORTH-NORTHWESTWARD TO POLEWARD TRACK AND A
SECOND GROUPING CONSISTING OF THE ECMWF, ECMWF ENSEMBLE AND UKMET
MODEL DEPICTING A STEADY NORTHWESTWARD TRACK. IN BOTH SCENARIOS,
RIDGING TO THE NORTH OF THE SYSTEM WEAKENS IN THE NEAR TERM IN
RESPONSE TO A DEVELOPING MID-LATITUDE TROUGH. IN THE EXTENDED
PERIOD, THE ECMWF MODEL GROUP INDICATES THAT, IN THE WAKE OF THE
TROUGH, A RIDGE WILL BUILD TO THE NORTH OF TY 11W AND TAKE OVER AS
THE DOMINANT STEERING MECHANISM. THIS RIDGE WILL BRING THE SYSTEM ON
A TRAJECTORY TO THE WEST OF THE OTHER MODEL GROUP. THE ECMWF
GROUPING APPEARS MORE PROBABLE GIVEN AN ANTICIPATED ZONAL MID-
LATITUDE FLOW PATTERN AND THE CURRENT JTWC
TRACK FORECAST IS HEDGED WEST OF THE CONSENSUS TO REFLECT THIS MORE
LIKELY SITUATION. ADDITIONAL ADJUSTMENTS MAY BE NECESSARY IN
SUBSEQUENT FORECASTS. GIVEN THE NOTED BIFURCATION IN THE MODEL
GUIDANCE, CONFIDENCE IN THE JTWC TRACK FORECAST IS LOW FOR THE
EXTENDED PERIOD. POOR OUTFLOW AND ENTRAINMENT OF MORE STABLE AIR ARE
EXPECTED TO GRADUALLY REDUCE INTENSITY TO 65 KTS BY TAU 120.//
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