Tropical Storm NEOGURI Advisory 17.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W (TWENTYONE)
WARNING NR 003//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 21W (TWENTYONE), LOCATED APPROXIMATELY
547 NM EAST-NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED
NORTH-NORTHWESTWARD AT 08 KNOTS (KTS) OVER THE PAST SIX HOURS.
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLC) WITH DEEP FLARING
CONVECTION LOCATED DIRECTLY OVER AND TO THE NORTHEAST OF THE LLC. THE
INITIAL POSITION IS PLACED WITH GOOD CONFIDENCE, SUPPORTED BY A
162356Z PARTIAL METOP-A ASCAT IMAGE. SET AT 30 KTS, THERE IS GOOD
CONFIDENCE IN THE INITIAL INTENSITY OF TD 21W BASED ON A DVORAK
CURRENT INTENSITY ESTIMATE OF T1.5/25 KTS FROM PGTW. ADDITIONALLY THE
AFOREMENTIONED ASCAT PASS SHOWS SMALL SWATHS OF 30 KTS WINDS IN THE
NORTHEAST QUADRANT. TD 21W REMAINS IN A FAVORABLE ENVIRONMENT WITH
LOW (05-15 KTS) VERTICAL WIND SHEAR (VWS), STRONG POLEWARD OUTFLOW,
AND HIGH (29-31 CELSIUS) SEA SURFACE TEMPERATURE (SST). TD 21W IS
TRACKING NORTH-NORTHWESTWARD AS A BREAK BETWEEN TWO SUBTROPICAL
RIDGES (STR) TO THE NORTH ALLOWS NORTHWARD MOVEMENT OF TD 21W.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. THROUGH TAU 36, TD 21W WILL TRACK WEST-NORTHWESTWARD PRIOR TO
TURNING WESTWARD AS THE SYSTEM IS STEERED BY THE STR LOCATED TO THE
NORTH. A NORTHEAST SURGE NEAR LUZON IS EXPECTED TO STEER THE SYSTEM
WEST-SOUTHWESTWARD AFTER TAU 36. UPPER LEVEL DIVERGENCE REMAINS
OFFSET TO THE NORTHEAST AND WILL SLOWLY DECREASE OVER THE NEXT 24-36
HOURS. NEAR LUZON, INTERACTION WITH THE NORTHEAST SURGE WILL
GRADUALLY DISSIPATE TD 21W. NUMERICAL MODEL GUIDANCE HAS IMPROVED IN
THE LAST SIX HOURS DESPITE THE WEAK NATURE OF THE SYSTEM. THE MODELS
ARE IN FAIR AGREEMENT WITH SLIGHT OUTLIERS TO THE NORTH (GFS) AND
SOUTH (NAVGEM), PLACING MODERATE CONFIDENCE IN THE JTWC FORECAST TRACK.//
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