Tropical Storm SANBA Advisory mié, 12-09

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SANBA) WARNING NR 10//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 17W (SANBA), LOCATED APPROXIMATELY 700 NM SOUTH OF
KADENA, OKINAWA, JAPAN, HAS TRACKED NORTH-NORTHWESTWARD AT 07 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) REVEALS A 14 NM EYE HAS DEVELOPED OVER THE PAST FEW HOURS AS
THE SYSTEM CONTINUES TO UNDERGO RAPID INTENSIFICATION. A 122316Z
SSMIS 91 GHZ MICROWAVE IMAGE DEPICTS A VERY SOLID CENTRAL CORE OF
DEEP CONVECTION WITH A SMALL EYE. THE CURRENT POSITION IS BASED ON
THIS IMAGERY WITH GOOD CONFIDENCE. ANIMATED WATER VAPOR IMAGERY
INDICATES ROBUST RADIAL OUTFLOW WITH AN EXCELLENT POLEWARD CHANNEL.
THIS POLEWARD FLOW IS BEING ENHANCED BY A TUTT CELL TO THE NORTHEAST
AS WELL AS A SUBTROPICAL LOW (LOCATED SOUTHEAST OF HONSHU) WHICH IS
HELPING TO PRODUCE 40-50 KNOT WESTERLY FLOW NORTH OF THE SYSTEM.
BASED ON THE CONTINUED IMPROVEMENT IN SATELLITE PRESENTATION AND
DVORAK ESTIMATES FROM PGTW AND RJTD, THE INITIAL INTENSITY IS
ASSESSED AT 90 KNOTS. THE MOST RECENT 500 MB ANALYSIS AND SATELLITE
IMAGERY DEPICT A MAJOR SHORT-WAVE TROUGH CURRENTLY DEEPENING OVER
CENTRAL AND EASTERN CHINA. THE CIMSS VERTICAL WIND SHEAR (VWS)
PRODUCT SHOWS LIGHT (05 KT) SHEAR OVER 17W. SEA SURFACE TEMPERATURES
ARE HIGHLY FAVORABLE AT AROUND 30 DEGREES CELSIUS, AND SHOULD REMAIN
FAVORABLE UNTIL POLEWARD OF 32 DEGREES LATITUDE.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 17W IS TRACKING NORTH-NORTHWESTWARD, ALONG THE WESTERN
PERIPHERY OF THE NEAR-EQUATORIAL RIDGE (NER). THE SYSTEM IS EXPECTED
TO CONTINUE THIS MOTION THROUGH TAU 72. THERE IS HIGH CONFIDENCE IN
THIS PORTION OF THE TRACK BASED ON THE TIGHT AGREEMENT AMONG DYNAMIC
MODELS. GFDN IS THE SOLE OUTLIER, TAKING THE SYSTEM TO THE EAST TO
OKINAWA. GIVEN THE FAVORABLE ENVIRONMENTAL CONDITIONS AS WELL AN
ENHANCEMENT TO POLEWARD OUTFLOW EXPECTED AS THE SHORTWAVE TROUGH
APPROACHES, TY 17W IS FORECAST TO CONTINUE INTENSIFYING OVER THE
NEXT 48 HOURS. A PEAK INTENSITY OF 125 KNOTS IS FORECAST AT TAU 48.
   C. IN THE EXTENDED TAUS, THERE IS LOW CONFIDENCE IN THE TRACK
FORECAST DUE TO UNCERTAINTY IN THE DEPTH AND ORIENTATION OF THE
AFOREMENTIONED MAJOR SHORTWAVE TROUGH AS IT DIGS INTO THE YELLOW SEA
AND EAST CHINA SEA. DYNAMIC MODEL GUIDANCE DIVERGES WITH A LARGE 350
NM SPREAD AT TAU 120. ECMWF REMAINS THE WESTERN-MOST OUTLIER, BUT
HAS BEEN TRENDING EASTWARD AND NOW RE-CURVES THE SYSTEM INTO
NORTHWEST NORTH KOREA AFTER TAU 120. GFDN IS THE EASTERN-MOST
OUTLIER, AND TAKES THE SYSTEM TOWARDS SASEBO, JAPAN. THIS SCENARIO
IS UNLIKELY, HOWEVER, GIVEN THE RIDGING EXPECTED TO BE IN PLACE OVER
SOUTHWESTERN JAPAN. THE REMAINDER OF THE GUIDANCE RE-CURVES THE
SYSTEM TOWARD SOUTH KOREA WITH VARYING SOLUTIONS BASED ON THE
FORECAST STRENGTH OF THE SUBTROPICAL RIDGE. AFTER TAU 96, TY 17W
WILL START TO RAPIDLY WEAKEN DUE TO INCREASING VWS ASSOCIATED WITH
THE SHORTWAVE TROUGH AND WILL BEGIN EXTRA-TROPICAL TRANSITION AFTER
TAU 120.//
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