Tropical Storm SURIGAE Advisory Sat Apr 17

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 02W (SURIGAE) WARNING NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
    TYPHOON (TY) 02W (SURIGAE), LOCATED APPROXIMATELY 264 NM
NORTHWEST OF KAYANGEL, PALAU, HAS TRACKED NORTHWESTWARD AT 12 KNOTS
(KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) REVEALS A 12 NM EYE WITH DEEP CONVECTIVE BANDS
WRAPPING INTO THE LOW LEVEL CIRCULATION CENTER, LENDING GOOD
CONFIDENCE TO THE INITIAL POSITION. THE INITIAL INTENSITY IS SET AT
120 KTS BASED ON DVORAK CURRENT INTENSITY ESTIMATE OF T6.0-6.5 (115-
127 KTS) BY PGTW, KNES, RJTD, AND RCTP. THE INITIAL WIND RADII DATA
HAVE BEEN UPDATED BASED ON RECENT SMAP DATA. ENVIRONMENTAL ANALYSIS
INDICATES ROBUST EQUATORWARD AND POLEWARD OUTFLOW, LOW (5-10 KTS)
VERTICAL WIND SHEAR, AND WARM (29-30 CELSIUS) SEA SURFACE
TEMPERATURES CONTRIBUTING TO AN OVERALL FAVORABLE ENVIRONMENT FOR
FURTHER DEVELOPMENT. TY 02W IS TRACKING TOWARDS A WEAKNESS IN THE
SUBTROPICAL RIDGE (STR) CAUSED BY AN APPROACHING MID-LATITUDE TROUGH.
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 AND CONTINUE TO
INTENSIFY THROUGH TAU 24, REACHING A PEAK OF 130 KTS. AFTERWARDS,
TRACK SPEED IS EXPECTED TO SLOW AS IT ENTERS A WEAK STEERING
ENVIRONMENT AROUND TAU 36. BY TAU 48, A BUILDING STR TO THE EAST
WILL TAKE OVER AS THE PRIMARY STEERING MECHANISM, TURNING TY 02W TO
A NORTHWARD TRACK AS IT MOVES ALONG THE WESTERN PERIPHERY OF THE
STR. AS IT BEGINS TO TRACK NORTH, THE DECREASING DIVERGENCE ALOFT
WILL CAUSE THE SYSTEM TO SLOWLY WEAKEN. NUMERICAL MODEL GUIDANCE IS
IN FAIR AGREEMENT DURING THE INITIAL PORTION OF THE FORECAST WITH A
CROSS-TRACK SPREAD OF 89 NM BY TAU 48. OF NOTE, THE LATEST NAVGEM
SOLUTION HAS SHIFTED TO THE WEST. OVERALL, THERE IS FAIR CONFIDENCE
IN THE EARLY PORTION OF THE JTWC FORECAST TRACK WHICH IS PLACED NEAR
THE MULTI-MODEL CONSENSUS.
   C. AFTER TAU 72, TY 02W WILL TRACK NORTHWARD ALONG THE WESTERN
PERIPHERY OF THE STR. AS IT MOVES NORTH, THE ENVIRONMENT WILL SLOWLY
BECOME LESS FAVORABLE AS UPPER LEVEL DIVERGENCE BEGINS TO
SIGNIFICANTLY DECREASE BY TAU 72, LEADING TO THE SYSTEM WEAKENING TO
85 KTS BY TAU 120. IN THE EXTENDED RANGE, NUMERICAL MODEL TRACK
SOLUTIONS DIVERGE TO A CROSS-TRACK SPREAD OF 447 NM AT TAU 120. THE
ECMWF SOLUTION CONTINUES TO BRING THE SYSTEM OVER LUZON BY TAU 120.
ADDITIONALLY, THE NAVGEM SOLUTION HAS SHIFTED IN LINE WITH THE ECMWF
SOLUTIONS IN THE LATEST MODEL RUNS. THE UKMET, UKMET ENSEMBLE, AND
JGSM MODEL GUIDANCE REMAIN THE EASTERNMOST SOLUTIONS. BASED ON THE
CROSS-TRACK SPREAD BETWEEN THE MODEL SOLUTIONS, THERE IS LOW
CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC TRACK FORECAST.//
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