Tropical Storm SANVU Advisory Fri May 25

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 03W (SANVU) WARNING NR 18//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 03W (SANVU), LOCATED APPROXIMATELY 100 NM SOUTHWEST
OF IWO TO, JAPAN, HAS TRACKED NORTH-NORTHEASTWARD AT 07 KNOTS OVER
THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY
(EIR) SHOWS COOLING CLOUD TOPS WITHIN THE TIGHTLY WRAPPED
CONVECTIVE BANDING AROUND TY SANVU'S LOW-LEVEL CIRCULATION CENTER
(LLCC). THIS EXPECTED INTENSIFICATION IS IN PART DUE TO THE COOLING
UPPER-LEVEL ATMOSPHERE AS TY 03W ENTERS INTO ANOTHER DIURNAL
MAXIMUM CYCLE. THERE IS HIGH CONFIDENCE IN THE INITIAL POSITION
BASED ON A CLEAR VIEW OF THE LLCC IN THE EIR AND ANOTHER TIMELY
MICROWAVE IMAGE FROM A 251102Z SSMIS PASS. THE INITIAL INTENSITY IS
SLIGHTLY INCREASED FROM THE LAST WARNING TO 80 KNOTS BASED ON AN
AVERAGE OF DVORAK ESTIMATES RANGING FROM 65-77 KNOTS FROM RJTD AND
PGTW/KNES RESPECTIVELY AND A 25/0700Z SATCON ESTIMATE OF 78 KNOTS.
UPPER-LEVEL ANALYSIS INDICATES THAT A POINT SOURCE OF DIFFLUENCE
REMAINS OVER THE LLCC. THERE IS CURRENTLY LOW TO MODERATE (10-20
KNOTS) WESTERLY VERTICAL WIND SHEAR (VWS) WITH STRONG DIFFLUENT
FLOW ALOFT AND TO THE EAST. ANIMATED WATER VAPOR IMAGERY INDICATES
THAT THE POLEWARD OUTFLOW INTO THE MID-LATITUDE WESTERLIES REMAINS
ROBUST. WEST-NORTHWEST OF TY 03W EXISTS AN AREA OF UPPER-LEVEL
CONVERGENCE ASSOCIATED WITH THE APPROACHING UPPER-LEVEL TROUGH. TY
SANVU IS POLEWARD OF THE STEERING SUBTROPICAL RIDGE (STR) AXIS AND
CONTINUES TO ACCELERATE NORTHEASTWARDS ALONG THE NORTHWESTERN
PERIPHERY OF THE STR.
3. FORECAST REASONING.
   A. THE FORECAST PHILOSOPHY HAS NOT CHANGED SINCE THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
   B. TY 03W HAS PROBABLY REACHED ITS MAXIMUM INTENSITY AND IS
FORECAST TO MAINTAIN IT THROUGH THE OVERNIGHT AND EARLY MORNING
DIURNAL MAXIMUM. A 250600Z OCEAN HEAT CONTENT (OHC) ANALYSIS
INDICATES THAT TY SANVU SEEMS TO HAVE PROPAGATED OUT OF A WARM POOL
AND NOW RESIDES IN A DRASTICALLY COOLER OHC ENVIRONMENT.
ADDITIONALLY, SEA SURFACE TEMPERATURES ARE CURRENTLY AT 26-27
DEGREES CELSIUS AND SHARPLY DROP OFF TO 23-25 DEGREES CELSIUS NORTH
OF 25 DEGREES NORTHERN LATITUDE. AFTER TAU 12, THE SYSTEM SHOULD
BEGIN TO GRADUALLY WEAKEN AS IT ENCOUNTERS INCREASED WESTERLY
VERTICAL WIND SHEAR, UPPER-LEVEL CONVERGENCE, AND A STEEP DROP OFF
IN SST AND OHC. BETWEEN TAU 36 AND TAU 48, TY 03W WILL BEGIN TO
INTERACT WITH THE BAROCLINIC ZONE, AND BY TAU 72 THE SYSTEM WILL
BECOME COMPLETELY EMBEDDED IN THE MID-LATITUDE WESTERLY FLOW AS A
STRONG EXTRA-TROPICAL LOW. THE NUMERICAL MODEL GUIDANCE REMAINS
TIGHTLY PACKED AND THEREFORE THE OFFICIAL JTWC FORECAST TRACK
AGREES WITH THE MODEL CONSENSUS. THERE IS HIGH CONFIDENCE IN THE
FORECAST TRACK BASED ON THE PERSISTENCE OF THE JTWC TRACK, MINIMAL
SPREAD IN THE DYNAMIC AIDS, AND ECMWF ENSEMBLE MEMBERS.//
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