THE INITIALINTENSITY OF 15KTS
WDPN31 PGTW 171500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 02W (SURIGAE) WARNING
NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUPER TYPHOON (STY) 02W (SURIGAE), LOCATED APPROXIMATELY 324 NM
EAST OF LEGAZPI, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 12 KNOTS
(KTS) OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY SHOWS A HIGHLY-SYMMETRICAL SYSTEM WITH A CENTRAL
DENSE OVERCAST (CDO) THAT CONTINUED TO DEEPEN WHILE MAINTAINING A
SHARPLY OUTLINED 16-NM EYE. FEEDER BANDS HAVE SHORTENED AND THINNED
OUT AS THEY SPIRALED TIGHTER INTO THE CDO. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE OVER THE WELL-DEFINED EYE. THE INITIAL
INTENSITY OF 15KTS IS BASED ON AN OVERALL ASSESSMENT OF AGENCY DVORAK
ESTIMATES OF T7.0/140KTS (PGTW/RCTP), T7.5/155KTS (RJTD); AND THE
OBJECTIVE ESTIMATES OF T7.9/167KTS (ADT) AND 152KTS (SATCON) THAT
REFLECTS THE GREATLY IMPROVED EIR SIGNATURE OF THE SYSTEM.
ENVIRONMENTAL ANALYSIS INDICATES ROBUST EQUATORWARD AND POLEWARD
OUTFLOW, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND WARM (29-30C) SEA
SURFACE TEMPERATURES IN THE PHILIPPINE SEA CONTRIBUTING TO AN OVERALL
FAVORABLE ENVIRONMENT. STY 02W IS TRACKING TOWARD A BREAK IN THE
RIDGE TO THE NORTH.
3. FORECAST REASONING.
A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
B. STY 02W WILL CONTINUE ON ITS CURRENT NORTHWESTWARD TRACK AND
INTENSIFY THROUGH TAU 12 TO A PEAK OF 135 KTS. AFTERWARD, IT IS
EXPECTED TO SLOW AS IT ENTERS A WEAK STEERING ENVIRONMENT. BY TAU 24,
THE SPLIT SUBTROPICAL RIDGE (STR) TO THE NORTHEAST WILL BUILD,
REORIENT AND TAKE OVER AS THE PRIMARY STEERING MECHANISM, DRIVING THE
CYCLONE TO A NORTHWARD TRAJECTORY. AS THE SYSTEM GAINS LATITUDE,
DIVERGENCE ALOFT WILL DECREASE AND CAUSE THE SYSTEM TO SLOWLY WEAKEN,
DOWN TO 110KTS BY TAU 72. NUMERICAL MODELS ARE IN FAIR AGREEMENT
DURING THIS PORTION OF THE FORECAST WITH A GRADUAL AND EVEN CROSS-
TRACK SPREAD TO 186NM BY TAU 72. THEREFORE, THERE IS FAIR CONFIDENCE
IN THIS PORTION OF THE JTWC FORECAST TRACK WHICH IS LAID OVER BUT
SLIGHTLY SLOWER THAN THE MULTI-MODEL CONSENSUS DURING THE SLOW
PROGRESSION IN THE WEAK STEERING SEGMENT.
C. AFTER TAU 72, STY SURIGAE WILL CONTINUE NORTHWARD ALONG THE
WESTERN PERIPHERY OF THE STR, CREST THE AXIS, THEN ACCELERATE
NORTHEASTWARD ON THE POLEWARD SIDE. AS IT MOVES FURTHER NORTH, THE
ENVIRONMENT WILL SLOWLY BECOME LESS FAVORABLE AS UPPER LEVEL
DIVERGENCE CONTINUES TO DECREASE LEADING TO GRADUAL WEAKENING,
DOWN TO 85KTS BY TAU 120. NUMERICAL MODELS HAVE CLUSTERED CLOSER AND
NO MEMBER TRACK TOWARD LUZON ANY LONGER. THE CROSS TRACK SPREAD IS
NOW DOWN TO 442NM AT TAU 120, LENDING FAIR CONFIDENCE IN THE EXTENDED
PORTION OF THE JTWC TRACK FORECAST.//
NNNN