Tropical Storm SANBA Advisory Mon Sep 10

MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 17W (SEVENTEEN)
WARNING NR 01//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL DEPRESSION (TD) 17W (SEVENTEEN), LOCATED
APPROXIMATELY 80 NM NORTH-NORTHWEST OF PALAU, HAS TRACKED WEST-
NORTHWESTWARD AT 10 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED
SATELLITE IMAGERY AND A 101612Z AMSU-B MICROWAVE IMAGE SHOW A
STRENGTHENING LOW LEVEL CIRCULATION CENTER WITH PERSISTENT DEEP
CONVECTION, PRIMARILY IN THE WESTERN AND NORTHERN SEMICIRCLES. THE
CURRENT INTENSITY IS BASED ON DVORAK ESTIMATES OF 25 KNOTS FROM KNES
AND PGTW. UPPER LEVEL ANALYSIS INDICATES 17W IS LOCATED DIRECTLY
BENEATH A POINT SOURCE ANTICYCLONE IN A REGION OF WEAK (5-10 KNOT)
VERTICAL WIND SHEAR. RECENT WATER VAPOR SATELLITE IMAGERY DEPICTS
GOOD RADIAL OUTFLOW HAS PERSISTED FOR SEVERAL HOURS. THIS SYSTEM IS
CURRENTLY BEING STEERED BY THE SOUTHWESTERN EXTENT OF A SUBTROPICAL
RIDGE (STR) TO THE EAST-NORTHEAST.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST
PHILOSOPHY.
   B. TD 17W IS CURRENTLY TRACKING ALONG THE SOUTHWESTERN PERIPHERY
OF AN EAST-WEST ORIENTED DEEP LAYER STEERING RIDGE. THIS STR IS
EXPECTED TO BECOME MORE POLEWARD ORIENTED, STEERING 17W IN A MORE
NORTHWESTWARD DIRECTION DURING THE NEXT 12 HOURS. THIS STR SHOULD
REMAIN THE PRIMARY STEERING INFLUENCE THROUGHOUT THE FORECAST
PERIOD, AND 17W IS EXPECTED TO TAKE ON A NORTH-NORTHWESTERLY TRACK
BEYOND TAU 12 THROUGH THE REMAINDER OF THE FORECAST PERIOD. TD 17W
IS EXPECTED TO GRADUALLY INCREASE IN INTENSITY DUE TO FAVORABLE SEA
SURFACE TEMPERATURES (26-30 DEGREES CELSIUS) AND A FAVORABLE UPPER
LEVEL ENVIRONMENT.
   C. IN THE EXTENDED FORECAST, 17W IS EXPECTED TO CONTINUE TRACKING
NORTH-NORTHWESTWARD ALONG THE WESTERN PERIPHERY OF THE STR. DUE TO
CONTINUED FAVORABLE ALONG-TRACK ENVIRONMENTAL CONDITIONS, 17W IS
EXPECTED TO GRADUALLY INCREASE IN INTENSITY THROUGH TAU 120. BY
THEN, 17W IS EXPECTED TO BE IN THE VICINITY OF OKINAWA. NUMERICAL
MODEL GUIDANCE IS SPREAD OUT WITH NOGAPS FAVORING A NORTHEASTERLY
TRACK AND WBAR, ECMWF AND GFS TRACKING NORTH-NORTHWESTERLY. THIS
INITIAL FORECAST FAVORS THE MORE NORTH-NORTHWESTERLY TRACK WITH LOW
CONFIDENCE.//
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