Tropical Storm SAOLA Advisory so., 28.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (SAOLA) WARNING NR 33//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TYPHOON (TY) 27W (SAOLA), LOCATED APPROXIMATELY 61 NM SOUTH OF KADENA
AB, OKINAWA, JAPAN, HAS TRACKED NORTHWARD AT 12 KNOTS OVER THE PAST
SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE
SYSTEM HAS DEVELOPED A LARGE AND RAGGED BANDING EYE THAT IS NOT QUITE
CLOSED. THE DEEP CONVECTIVE BANDS, MOSTLY FEEDING IN FROM THE WEST TO
SOUTHWEST HAVE WRAPPED TIGHTER INTO THE LOW LEVEL CIRCULATION. THE
INITIAL POSITION IS BASED ON THE MSI AND ON A RADAR COMPOSITE
REFLECTIVITY LOOP FROM OKINAWA WITH HIGH CONFIDENCE. THE INITIAL
INTENSITY OF 65 KNOTS IS BASED ON THE PGTW DVORAK ESTIMATE OF T4.0
AND REFLECTS THE UPGRADED STATUS OF TY 27W. UPPER-LEVEL ANALYSIS
INDICATES THE SYSTEM IS NOW IN AN AREA OF MODERATE TO STRONG (20-25
KNOT) VERTICAL WIND SHEAR (VWS). THERE IS ALSO STRONG SUBSIDENCE
ALONG THE WESTERN SEMI-CIRCLE CAUSED BY THE LEADING EDGE OF A
MID-LATITUDE TROUGH DIGGING IN FROM CHINA. IN THE SAME AREA, A ROBUST
NORTHERLY LOW LEVEL DRY AIR ENTRAINMENT IS EVIDENT ON THE MSI LOOP.
HOWEVER, VERY STRONG EQUATORWARD AND POLEWARD OUTFLOW, ENHANCED BY
INITIAL EXPOSURE INTO THE PREVAILING WESTERLIES, PLUS WARM SSTS AT 28
CELSIUS, ARE OFFSETTING THESE NEGATIVE EFFECTS AND CAUSING NEAR-TERM
INTENSIFICATION. THE CYCLONE IS ROUNDING THE WESTERN EDGE OF A
DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE EAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE IN THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY SAOLA WILL BEGIN TO RECURVE AND ACCELERATE NORTHEASTWARD AS
IT GETS EMBEDDED IN THE MID-LATITUDE WESTERLIES. IT WILL PASS OVER
EASTERN OKINAWA THEN SKIRT THE SOUTHERN COAST OF MAINLAND JAPAN. THE
ENHANCED POLEWARD OUTFLOW WILL PREVAIL AND INTENSIFY 27W TO A PEAK OF
75 KNOTS BY TAU 24. AFTERWARD, THE STRONG WINDS WILL TRANSLATE TO
STRONG VWS. ADDITIONALLY, COOL DRY AIR ADVECTION AND COOLING SSTS,
CONCURRENT WITH EXTRA-TROPICAL TRANSITION (ETT) BY TAU 36, WILL
STEADILY ERODE THE SYSTEM. BY TAU 48, THE SYSTEM WILL BECOME A
STORM-FORCE COLD CORE LOW WITH A RAPIDLY EXPANDING WIND FIELD IN THE
PACIFIC OCEAN SOUTHEAST OF HOKKAIDO. THE DYNAMIC MODEL GUIDANCE IS IN
OVERALL GOOD AGREEMENT WITH THE FORECAST TRACK. HOWEVER, AS TYPICAL
WITH RECURVE SCENARIOS, THERE IS SIGNIFICANT DIFFERENCES IN THE
LATERAL SPEED AMONG THE TRACK MEMBERS. THE TRACK SPEEDS DIFFER EVEN
GREATER AT THE ETT PHASE. IN VIEW OF THIS, THERE IS FAIR CONFIDENCE
IN THE JTWC TRACK FORECAST UP TO TAU 24, THEN LOW CONFIDENCE
AFTERWARD.//
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