Tropical Storm SAOLA Advisory ср, 25.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (SAOLA)
WARNING NR 21//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM 27W (SAOLA), LOCATED APPROXIMATELY 256 NM NORTH OF
YAP, HAS TRACKED WESTWARD AT 24 KNOTS OVER THE PAST SIX HOURS.
ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS THE MAIN
CONVECTIVE AREA SHEARED SOUTHWESTWARD OF THE WEAK AND POORLY
ORGANIZED LOW LEVEL CIRCULATION CENTER (LLCC). OVER THE PAST 6
HOURS, THERE HAS BEEN A FLARE UP OF WEAK CONVECTION NEAR THE LLCC,
BUT THE MAJORITY OF THE DEEPEST ACTIVITY REMAINS ISOLATED TO THE
SOUTHWEST QUADRANT. A 241036Z OSCAT SCATTEROMETER PASS INDICATED
THAT THE LLCC WAS FURTHER SOUTH THAN THE ORIGINAL 241200Z INITIAL
POSITION, LEADING TO A RELOCATION OF THE 1200Z BEST TRACK POSITION
SIGNIFICANTLY SOUTHWARD. THE CURRENT (241800Z) INITIAL POSITION
CONTINUES THE TREND OF WESTWARD MOVEMENT SEEN OVER THE PREVIOUS 12
HOURS, THOUGH THE POSITION IS PLACED WITH RELATIVELY LOW CONFIDENCE
BASED ON THE AVAILABLE INFRARED IMAGERY. A 241536Z NPP ATMS
MICROWAVE IMAGE SHOWED A BROAD, ILL-DEFINED LLCC, WHICH ASSISTED IN
THE PLACEMENT OF THE INITIAL POSITION. THE INITIAL INTENSITY OF 35
KNOTS IS BASED ON A COMBINATION OF DVORAK CURRENT INTENSITIES OF 2.5
(35 TO 45 KTS) FROM PGTW AND RJTD, AND AUTOMATED DVORAK INTENSITIES
OF 2.3 (33 KTS). THE INTENSITY ESTIMATE IS ALSO SUPPORTED BY THE
OSCAT PASS SHOWING MOSTLY 30 KNOT WIND BARBS WITH ONLY A COUPLE 35
KNOT BARBS. ENVIRONMENTAL CONDITIONS REMAIN MARGINAL, WITH MODERATE
TO UNFAVORABLE (15-25 KNOTS) EASTERLY VERTICAL WIND SHEAR (VWS) AND
HIGH SEA SURFACE TEMPERATURES (31 DEG CELSIUS). THE MAIN LIMITING
FACTOR IS THE RAPID MOVEMENT AND THE LIMITED OUTFLOW, WHICH IS BEING
HINDERED BY AN UPPER-LEVEL INVERTED TROUGH JUST EAST OF THE SYSTEM,
BRINGING CONVERGENT FLOW TO THE NORTH SIDE OF THE SYSTEM. CURRENTLY
THERE ARE INDICATIONS OF A WEAK POLEWARD CHANNEL DEVELOPING TO THE
NORTHWEST OF THE SYSTEM. TS SAOLA CONTINUES TO TRACK RAPIDLY
WESTWARD UNDER THE INFLUENCE OF A DEEP SUBTROPICAL RIDGE (STR)
LOCATED TO THE NORTHEAST. THE TRACK HAS FLATTENED SIGNIFICANTLY OVER
THE PAST TWELVE HOURS AS THE STR HAS BUILT WESTWARD, FORCING 27W TO
A WESTWARD TRACK.
3. FORECAST REASONING.
   A. THE SHORT-TERM TRACK HAS SHIFTED SIGNIFICANTLY SOUTHWARD BASED
ON THE UPDATED INITIAL POSITION.
   B. TS 27W WILL CONTINUE TO TRACK TO THE WEST-NORTHWEST FOR THE
NEXT 12 HOURS ALONG THE SOUTHWESTERN PERIPHERY OF THE STR. BY TAU
24, THE STR BEGINS TO REORIENT TO A MORE NORTH-SOUTH ORIENTATION,
WHILE SIMULTANEOUSLY A BREAK IN THE RIDGE PATTERN DEVELOPS NEAR 13OE
LONGITUDE, ALLOWING SAOLA TO TURN NORTHWARD AFTER TAU 36. TRACK
SPEEDS WILL SLOW FROM TAU 12 THROUGH 72, AS THE SYSTEM ENTERS A
WEAKER STEERING ENVIRONMENT AS IT APPROACHES THE WEAKNESS IN THE
RIDGE. THE GENERALLY NORTHWARD TRACK WILL PERSIST UNTIL THE SYSTEM
ROUNDS THE RIDGE AXIS NEAR TAU 60, SOUTHEAST OF OKINAWA, THEREAFTER
ACCELERATING AND TURNING NORTHEASTWARD. THE SYSTEM IS FORECAST TO
MAINTAIN INTENSITY FOR 12 HOURS DUE TO THE PERSISTENCE OF THE
CONVERGENT FLOW ON THE NORTH SIDE AND WEAK OUTFLOW CONDITIONS. SLOW
INTENSIFICATION RESUMES THROUGH TAU 72, AS THE SYSTEM MOVES INTO A
BETTER OUTFLOW ENVIRONMENT, ESTABLISHES A POLEWARD CHANNEL AND VWS
DECREASES, PEAKING AT 70 KNOTS BY TAU 72 AS IT ROUNDS THE RIDGE
AXIS. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 24,
THOUGH THE JTWC FORECAST IS TO SOUTH OF ALL MODEL GUIDANCE THROUGH
TAU 24, IN RESPONSE TO THE CURRENT MOTION TO THE WEST. BEYOND THIS
POINT THE JTWC TRACK BECOMES MORE IN LINE WITH THE MULTI-MODEL
CONSENSUS, THOUGH THE OVERALL SPREAD OF THE MODELS INCREASES AFTER
TAU 48. ECMWF AND GFS ARE THE WESTERN OUTLIERS, SHOWING A LANDFALL
OVER OKINAWA AROUND TAU 84. NAVGEM AND HWRF ARE THE EASTERN
OUTLIERS, SOME 400NM EAST OF OKINAWA. WITH THE HIGH DEGREE OF
UNCERTAINTY BEYOND TAU 48, AND THE RECENT TRACK CHANGES, THERE IS
LOW CONFIDENCE IN THIS PORTION OF THE JTWC TRACK FORECAST.
   C. AFTER TAU 72, TS 27W WILL ROUND THE STR AXIS, ACCELERATING
RAPIDLY TO THE NORTHEAST THROUGH THE END OF THE FORECAST PERIOD. AS
THE SYSTEM BEGINS TO INTERACT WITH AN APPROACHING MID-LATITUDE
TROUGH, IT COULD POTENTIALLY REACH A SLIGHTLY HIGHER INTENSITY THAN
SHOWN ON THE FORECAST, AFTER TAU 72, BEFORE THE BEGINNING OF
EXTRATROPICAL TRANSITION (ET). AS THE SYSTEM PASSES 30 DEG NORTH BY
TAU 96, IT WILL BEGIN TO UNDERGO ET BECOMING FULLY ET BY TAU 120.
DYNAMIC MODEL GUIDANCE HAS SIGNIFICANT SPREAD AND UNCERTAINTY IN THE
LATER PERIOD OF THE FORECAST, BOTH CROSS AND ALONG TRACK. THE JTWC
TRACK IS NEAR THE CONSENSUS, BUT SLIGHTLY FASTER. THE PRINCIPLE
OUTLIERS ARE GFS AND HWRF, BOTH INDICATING A SHARPER TURN AND LYING
TO THE SOUTH OF THE JTWC TRACK, WHILE UKMET INDICATES A SHALLOWER
TURN AND TAKES THE SYSTEM OVER THE KANTO PLAN. ADDITIONALLY, THE
MODELS BEGIN TO DIVERGE ON SYSTEM SPEED AFTER TAU 72, CREATING A
HIGH DEGREE OF UNCERTAINTY BY THE END OF THE FORECAST PERIOD. DUE TO
THE VARIABILITY IN BOTH TRACK AND SPEED, THERE IS LOW CONFIDENCE IN
THIS PORTION OF THE JTWC OFFICIAL FORECAST.//
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