Tropical Storm SURIGAE Advisory Fri Apr 16

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 02W (SURIGAE) WARNING NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
    TYPHOON (TY) 02W (SURIGAE), LOCATED APPROXIMATELY 42 NM NORTH OF
KAYANGEL, PALAU HAS TRACKED WEST-SOUTHWESTWARD AT 06 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTI-SPECTRAL SATELLITE IMAGERY SHOWS
TIGHTLY CURVED BANDING HAS NOW COMPLETELY WRAPPED AROUND THE
OBSCURED LOW-LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION
IS BASED IN A 160056Z METOP-B ASCAT PASS SHOWING A TIGHTLY WRAPPED
CIRCULATION. THE INITIAL INTENSITY, WHICH HAS INCREASED TO 75 KNOTS,
IS BASED ON THE DVORAK CURRENT INTENSITY ESTIMATES OF T4.5 (77
KNOTS) BY PGTW, RJTD AND KNES AND AN ADVANCED DVORAK TECHNIQUE
ESTIMATE OF 75 KNOTS. ENVIRONMENTAL ANALYSIS INDICATES A FAVORABLE
ENVIRONMENT FOR FURTHER INTENSIFICATION WITH LOW (<15KT) VERTICAL
WIND SHEAR (VWS), AND WARM (29-30C) SEA SURFACE TEMPERATURES (SST)
IN THE PHILIPPINE SEA. TY 02W IS CURRENTLY TRACKING ALONG THE
SOUTHERN PERIPHERY OF AN EXTENSION OF THE DEEP LAYER SUBTROPICAL
RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 02W IS FORECAST TO TRACK NORTHWESTWARD AS A MIDLATITUDE
TROUGH TO THE NORTHWEST DEEPENS AND BREAKS THE EXTENSION OF THE STR
AROUND TAU 48, CAUSING TY 02W TO TURN NORTHWARD. THE SYSTEM WILL
STEADILY INTENSIFY DUE TO ROBUST UPPER-LEVEL OUTFLOW CAUSED BY THE
MIDLATITUDE TROUGH WITH TY 02W REACHING 115KTS BY TAU 48. NUMERICAL
MODEL GUIDANCE REMAINS IN FAIR AGREEMENT WITH A CROSS-TRACK SPREAD
OF 170NM AT TAU 72 WITH ECMWF AND ECMWF ENSEMBLE MEAN CONTINUING TO
REMAIN FURTHER WEST OF THE REST OF THE MODELS. THE JTWC TRACK HAS
BEEN PLACED NEAR THE MULTI-MODEL CONSENSUS WITH GOOD CONFIDENCE IN
THE EARLY PORTION OF THE JTWC TRACK FORECAST.
   C. AFTER TAU 72, THE EASTERN PORTION OF THE BREAK IN THE STR
TAKES OVER AS THE PRIMARY STEERING MECHANISM, CAUSING TY SURIGAE TO
TRACK NORTHWARD THEN NORTH-NORTHEASTWARD AROUND THE WESTERN
PERIPHERY OF THIS RIDGE. THE ENVIRONMENTAL CONDITIONS WILL BECOME
SLIGHTLY LESS FAVORABLE AS THE AMOUNT OF UPPER-LEVEL DIVERGENCE
DECREASES AND SEA SURFACE TEMPERATURES LOWER THROUGH THE END OF THE
FORECAST PERIOD. THE SYSTEM WILL DECREASE DOWN TO 100KTS BY TAU 120.
NUMERICAL MODEL CROSS-TRACK SPREAD IS 350NM AT TAU 120 AS TRACK
SOLUTIONS DIVERGE FURTHER, LENDING LOW CONFIDENCE TO THE EXTENDED
PORTION OF THE JTWC TRACK FORECAST.//
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