Tropical Storm SAOLA Advisory Fri Oct 27

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (SAOLA)
WARNING NR 27//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM 27W (SAOLA), LOCATED APPROXIMATELY 533 NM SOUTH-
SOUTHEAST OF KADENA AB, HAS TRACKED NORTHWESTWARD AT 09 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
AND A 260414Z 89GHZ AMSR2 IMAGE SHOWS A PARTIALLY EXPOSED LOW LEVEL
CIRCULATION CENTER (LLCC) WITH BANDING CONVECTION WRAPPING IN FROM
THE WEST AND SOUTHERN PERIPHERIES, AND IS THE BASIS FOR THE INITIAL
POSITION. THE INITIAL INTENSITY IS ASSESSED AT 45 KNOTS WHICH IS
BASED ON AGENCY DVORAK ESTIMATES OF T3.0 (45 KNOTS), A PREVIOUS
260001Z OSCAT IMAGE SHOWING 40 KNOTS ON THE SOUTHWESTERN QUADRANT,
AND A 260416Z SATCON ESTIMATE OF 51 KNOTS. UPPER-LEVEL ANALYSIS
SHOWS AN ANTICYCLONE JUST NORTHEAST OF TS 27W CREATING STRONG
EASTERLY CONDITIONS, WITH A WELL ESTABLISHED RIDGE PROTRUDING
WESTWARD LIMITING THE POLEWARD OUTFLOW CHANNEL. DESPITE THE
PREVALENT EASTERLIES TS 27W IS STRUGGLING TO CREATE A POINT SOURCE
OVER THE LLCC, EVIDENCED BY WEAK ANTICYCLONIC ROTATION AND
RELATIVELY LOW VERTICAL WIND SHEAR. SSTS IN THE REGION ARE ALSO NOT
IMPRESSIVE AT 27 TO 28 CELSIUS, BUT ARE STILL RELATIVELY WARM TO
FUEL CYCLOGENESIS. CURRENTLY TS 27W IS TRACKING TO THE NORTHWEST
ALONG THE SOUTHWESTERN EXTENT OF A MID-TO-LOW LEVEL SUBTROPICAL
RIDGE (STR) LOCATED TO THE NORTHEAST.
3. FORECAST REASONING.
   A. NO CHANGE IN THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE, HOWEVER THE FORECAST TRACK HAS SHIFTED
WESTWARD NOW MAKING LANDFALL OVER OKINAWA NEAR TAU 48.
   B. TS 27W IS FORECAST TO CONTINUE ON ITS NORTHWESTWARD TRACK OVER
THE NEXT 36 TO 48 HOURS GUIDED BY THE EASTERN EDGE OF THE STR. THE
UPPER-LEVEL RIDGE IS FORECAST TO WEAKEN GRADUALLY OVER THE NEXT 12
TO 48 HOURS IMPROVING OUTFLOW CONDITIONS AND TS 27W IS EXPECTED TO
GRADUALLY INTENSIFY. JUST BEFORE TAU 48 A SHORTWAVE TROUGH WILL MOVE
INTO THE REGION FURTHER WEAKENING THE RIDGE AND ENHANCING THE
POLEWARD OUTFLOW CHANNEL LEADING TO A FASTER RATE OF
INTENSIFICATION, REACHING A PEAK INTENSITY OF 75 KNOTS, AND A SHIFT
IN TRACK MOTION TO THE NORTH EAST AS IT ROUNDS THE RIDGE AXIS.
DYNAMIC MODEL GUIDANCE SHOWS DIVERGENCE IN THE SHORT-TERM TRACK
RELATED TO THE STRENGTH OF THE MID-LEVEL SHORTLY BEFORE AND DURING
THE TROUGH PASSAGE. THE GFS SOLUTION HAS PROVEN TO BE THE MOST
CONSISTENT OVER THE LAST SEVERAL DAYS AS THE FAR WESTERN OUTLIER
WITH NAVGEM AND ECMWF ONLY RECENTLY FAVORING A WESTWARD TRACK. THE
FORECAST TRACK IS NOW BIASED TOWARD THESE SOLUTIONS WITH A TRACK
DIRECTLY OVER THE ISLAND OF OKINAWA.
   C. IN THE EXTENDED FORECAST, TS 27W WILL ACCELERATE EAST-
NORTHEASTWARD JUST AFTER TAU NEAR TAU 60 ONCE CAPTURED BY THE MID-
LEVEL TROUGH. THIS WILL COINCIDE WITH A COLD SURGE EVENT OVER THE
SEA OF JAPAN AND EAST CHINA SEA ENHANCING THE GALE FORCE WIND
DISTRIBUTION. TS 27W WILL BEGIN TRANSITIONING INTO COLD CORE LOW
AROUND TAU 72 AS THE COOL DRY AIR AND BAROCLINIC INSTABILITY RAPIDLY
DETERIORATE THE SYSTEM. THE UPPER-LEVEL JET IS FORECAST TO
STRENGTHEN AND REMAIN FAIRLY ZONAL OVER THE SOUTHERN PORTION OF THE
JAPANESE ISLANDS, INCREASING VERTICAL WIND SHEAR AND KEEPING THE
TRACK FURTHER SOUTH. DYNAMIC MODELS DIVERGE SIGNIFICANTLY AFTER TAU
72 WITH GFS AND NOW ECMWF SHOWING TRACK SOUTH OF 30 DEGREES NORTH,
AND MOST OTHERS SKIRTING THE SOUTHERN COASTLINE OF HONSHU. NAVGEM
KEEPS THE SYSTEM QUASI-STATIONARY JUST AFTER TAU 48 DUE TO AN
UNREALISTIC STRENGTHENING MID-LEVEL RIDGE WHILE THE TROUGH MOVES
THROUGH. BECAUSE OF THE UNCERTAINTY IN AVAILABLE GUIDANCE, THERE IS
STILL LOW CONFIDENCE IN THE FORECAST TRACK. GIVEN THE RECENT
CONSISTENCY IN THE GFS SOLUTION, PERFORMANCE RECORD WITH ECMWF, AND
AGREEMENT BETWEEN THE TWO, THE JTWC FORECAST TRACK HEDGED TOWARD
THESE SOLUTIONS.//
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