Tropical Storm LAN Advisory lun, 16-10

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (LAN)
WARNING NR 03//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 25W (LAN), LOCATED APPROXIMATELY 156 NM WEST-
NORTHWEST OF YAP, HAS TRACKED NORTHWESTWARD AT 09 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
SHOWS DEEP CONVECTION WRAPPING AROUND THE SOUTHERN AND EASTERN
QUADRANTS OF A GRADUALLY ORGANIZING LOW-LEVEL CIRCULATION CENTER.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE NEAR
OVERSHOOTING TOPS VISIBLE IN THE MSI. THE INITIAL INTENSITY IS SET
AT 35 KNOTS BASED ON A DVORAK ESTIMATE OF T2.5 FROM PGTW. UPPER-
LEVEL ANALYSIS INDICATES THE SYSTEM IS IN AN AREA OF MODERATE
VERTICAL WIND SHEAR (20-25 KNOTS), BUT IS SITUATED ALONG A SHEAR
GRADIENT, WHICH IS INDICATIVE OF DECENT POLEWARD OUTFLOW. SEA
SURFACE TEMPERATURES REMAIN WARM (30 DEGREES C) AS THE SYSTEM
TRACKS TOWARD THE NORTHWEST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 25W WILL CONTINUE TO TRACK TOWARD THE NORTHWEST IN THE
SHORT TERM. AFTER 24 TO 36 HOURS, THE SYSTEM IS EXPECTED TO TURN
TOWARD THE NORTH IN RESPONSE TO A MID-LATITUDE TROUGH DIGGING
THROUGH JAPAN AS THE STEERING SUBTROPICAL RIDGE (STR) AMPLIFIES
TOWARD THE EAST. FAVORABLE ENVIRONMENTAL CONDITIONS WILL PERSIST
AND ALLOW FOR STEADY INTENSIFICATION. BY TAU 72, TS 25W IS EXPECTED
TO BECOME A 90 KNOT SYSTEM.
   C. AFTER TAU 72, TS 25W WILL CONTINUE ITS NORTHWARD TRACK UNDER
THE STEERING INFLUENCE OF THE STR TO THE EAST, WITH A GRADUAL TURN
TOWARD THE NORTH-NORTHEAST AT LATER TAUS. GIVEN WARM SEA SURFACE
TEMPERATURES AND FAVORABLE UPPER-LEVEL CONDITIONS, A PERIOD OF
RAPID INTENSIFICATION REMAINS A POSSIBILITY AS THE SYSTEM GAINS
LATITUDE AND UPPER-LEVEL OUTFLOW IS ENHANCED BY SYNOPTIC FORCING
AHEAD OF THE MID-LATITUDE TROUGH. GLOBAL MODELS ARE IN GOOD
AGREEMENT WITH THE GENERAL NORTHWARD MOTION, ALTHOUGH THE TIMING OF
THE TURN IS STILL A BIT UNCERTAIN. FURTHERMORE, THE GFS AND NAVGEM
SUGGEST THAT MULTIPLE CIRCULATIONS COULD FORM ON THE EASTERN
PERIPHERY OF TS 25W, WHICH WOULD COMPLICATE THE DYNAMICS. ON THE
OTHER HAND, THE ECMWF SUGGESTS THAT TS 25W WILL REMAIN THE DOMINANT
CIRCULATION. THUS, THERE IS GOOD CONFIDENCE IN THE INITIAL JTWC
TRACK FORECAST, BUT LOW CONFIDENCE THEREAFTER UNTIL THE FUTURE
STRUCTURE OF TS 25W BECOMES MORE CERTAIN.//
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