Tropical Storm KROSA Advisory czw., 08.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (KROSA) WARNING NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 11W (KROSA), LOCATED APPROXIMATELY 174 NM SOUTH-
SOUTHWEST OF IWO TO, HAS TRACKED NORTHWESTWARD AT 03 KNOTS (KTS)
OVER THE PAST SIX HOURS. THERE IS HIGH CONFIDENCE IN THE INITIAL
POSITION BASED ON A PARTIALLY OBSCURED EYE FEATURE IN ANIMATED
MULTISPECTRAL SATELLITE IMAGERY. ANIMATED ENHANCED INFRARED IMAGERY
REVEALS THAT DEEP CONVECTION IS PRESENT IN 50 TO 75 PERCENT OF THE
EYEWALL AND THAT IS LIKELY INHIBITING THE EYE FROM BECOMING WELL
FORMED. THE INITIAL INTENSITY OF 75 KTS IS CONSISTENT WITH DVORAK
FIX INTENSITY ESTIMATES FROM KNES, RJTD, AND PGTW OF T4.5 (77 KTS).
WARM (29-30C) SEA SURFACE TEMPERATURE, GOOD EQUATORWARD AND POLEWARD
OUTFLOW CHANNELS, AND LOW (10-15 KT) VERTICAL WIND SHEAR MAKE THE
ENVIRONMENT FAVORABLE FOR INTENSIFICATION. AN INDUCED TROUGH TO THE
NORTH IS CAUSING SUBSIDENCE AHEAD OF THE CYCLONE THAT IS LIKELY
OFFSETTING THE OTHERWISE VERY FAVORABLE ENVIRONMENT. 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 SOMEWHAT FAVORABLE ENVIRONMENT WILL ALLOW SOME INTENSIFICATION TO
80 KTS BY TAU 12, HOWEVER, THE ENVIRONMENT WILL REMAIN MARIGNAL
OVERALL AND THE INTENSITY IS EXPECTED TO REMAIN NEAR STEADY STATE
THROUGH THIS PORTION OF THE FORECAST. NUMERICAL MODELS GENERALLY AGREE
WITH THE SHAPE OF THE TRACK. NOTABLY, THERE IS A CLUSTER OF MEMBERS
(ECMWF, GALWEM, AND UKMET) ON THE WESTERN SIDE OF THE ENVELOPE OF
SOLUTIONS. THE CURRENT TRACK FORECAST IS HEDGED WEST OF THE
CONSENSUS TO FAVOR THAT CLUSTER WITH FAIR CONFIDENCE DUE TO THE
SPREAD.
   C. ALTHOUGH THE WESTERN CLUSTER REMAINS, MODEL GUIDANCE CONTINUES
TO SPREAD IN THE EXTENDED FORECAST. ADDITIONALLY, OVERALL
DETERIORATING ENVIRONMENTAL CONDITIONS ARE EXPECTED TO GRADUALLY
REDUCE INTENSITY TO 60 KTS BY TAU 120. THE TRACK FORECAST REMAINS
COMPLEX ALTHOUGH THE GUIDANCE TENDS TO AGREE THAT RIDGING TO THE
NORTH OF THE SYSTEM WILL WEAKEN IN THE NEAR TERM IN RESPONSE TO A
DEVELOPING MID-LATITUDE TROUGH. IN THE EXTENDED PERIOD, THE WESTERN
CLUSTER 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. THE WESTERN CLUSTER APPEARS MORE PROBABLE AND THE JTWC
TRACK FORECAST CONTINUES TO BE HEDGED WEST OF THE CONSENSUS. GIVEN
THE SPREAD IS 390 NM AT TAU 120, CONFIDENCE IN THE JTWC TRACK
FORECAST IS LOW FOR THE EXTENDED PERIOD. //
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