Tropical Storm SANVU Advisory sáb, 26-05

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 03W (SANVU) WARNING NR 20//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 03W (SANVU), LOCATED APPROXIMATELY 155 NM
SOUTH-SOUTHWEST OF CHICHI JIMA, JAPAN, HAS TRACKED NORTHEASTWARD AT
09 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) AND A 252333Z SSMIS IMAGE CONTINUE TO INDICATE
WEAKENING ORGANIZATION WITH THE BULK OF THE DEEP CONVECTION NOW
CONFINED TO THE EASTERN SEMI-CIRCLE AS A RESULT OF THE PERSISTENT
WEAK TO MODERATE (10-15 KNOTS) WESTERLY VERTICAL WIND SHEAR (VWS) AND
UPPER-LEVEL CONVERGENCE. ADDITIONALLY, MSI AND THE TOTAL PRECIPITABLE
WATER LOOP SHOW DRY AIR ENTRAINMENT OVER THE WESTERN SEMI-CIRCLE THAT
MAY ALSO BE HINDERING DEEP CONVECTION FORMATION. DESPITE THE
WEAKENING CONVECTION, THE SYSTEM HAS MAINTAINED A RAGGED 20 NM EYE,
WHICH IS POSITIONED OVER IWO TO. AT 25/22Z SUSTAINED SURFACE WINDS
PEAKED AT 54 KNOTS WITH GUSTS OF 83 KNOTS BUT HAVE SINCE DECREASED
RAPIDLY TO LESS THAN 10 KNOTS WHILE SLP HAS BOTTOMED OUT AT 978 MB.
SURFACE WINDS ARE EXPECTED TO INCREASE AS THE SYSTEM TRACKS NORTHEAST
OF IWO TO. BASED ON THE EYE AND THE 252333Z SSMIS 37 GHZ IMAGE, THERE
IS GOOD CONFIDENCE IN THE CURRENT POSITION. THE CURRENT INTENSITY OF
75 KNOTS IS BASED ON DVORAK ESTIMATES OF 77 KNOTS FROM BOTH PGTW AND
KNES. TY SANVU IS TRACKING ALONG THE NORTHWESTERN PERIPHERY OF THE
DEEP SUBTROPICAL STEERING RIDGE. TRACK SPEEDS HAVE REMAINED
RELATIVELY SLOW DUE TO THE ZONAL UPPER-LEVEL FLOW PATTERN WITH THE
TIGHT GRADIENT CURRENTLY NORTH OF 30N. THIS IS EVIDENCED ON THE
25/12Z CHICHI JIMA (27N 142E) SOUNDING SHOWING MAXIMUM WESTERLY WINDS
OF ONLY 35 KNOTS AT 200 MB.
3. FORECAST REASONING.
   A. NO CHANGE IN THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
   B. TY 03W IS FORECAST TO TRACK ALONG THE NORTHWESTERN PERIPHERY OF
THE SUBTROPICAL RIDGE AT MODERATE SPEEDS THROUGH TAU 24. NEAR TAU 24,
THE SYSTEM IS EXPECTED TO ACCELERATE AND WEAKEN AS IT TRACKS INTO
STRENGTHENING MID-LATITUDE WESTERLY FLOW WITH INCREASING STRONG VWS,
OVER COOLER SST (LESS THAN 25C), AND BEGINS EXTRA-TROPICAL TRANSITION
(ETT). TY 03W IS EXPECTED TO COMPLETE ETT BY TAU 48 AS IT BECOMES
EMBEDDED WITHIN THE BAROCLINIC ZONE AND TRANSITIONS INTO A
STORM-FORCE EXTRA-TROPICAL LOW. DUE TO THE TIGHT CLUSTER OF DYNAMIC
GUIDANCE (135 NM SPREAD AT TAU 48) INCLUDING ENSEMBLE DATA, THERE IS
HIGH CONFIDENCE IN THE FORECAST TRACK.//
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