Tropical Storm BOLAVEN Advisory Tu, 21-08

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (BOLAVEN) WARNING
NR 02//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 16W (BOLAVEN), LOCATED APPROXIMATELY 420 NM
SOUTH OF IWO TO, HAS TRACKED NORTH-NORTHWESTWARD AT 06 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) DEPICTS A CONSOLIDATING LOW-LEVEL CIRCULATION CENTER (LLCC)
WITH IMPROVED CONVECTIVE BANDING WRAPPING INTO THE CENTER. A 200506Z
AMSU IMAGE SHOWS THAT THE BULK OF THE DEEP CONVECTION IS CONFINED TO
THE SOUTHERN SEMI-CIRCLE; HOWEVER, TIGHTLY-WRAPPED SHALLOW
CONVECTIVE BANDING IS EVIDENT OVER THE NORTHERN SEMI-CIRCLE AND,
ALONG WITH THE PGTW DVORAK ESTIMATE OF 35 KNOTS, SUPPORTS THE
UPGRADE TO TROPICAL STORM STRENGTH. THE INITIAL POSITION IS BASED ON
THE MSI AND AMSU IMAGE WITH GOOD CONFIDENCE. UPPER-LEVEL ANALYSIS
SHOWS A FAVORABLE ENVIRONMENT WITH RADIAL OUTFLOW ENHANCED BY A TUTT
CELL NEAR 35N 170E. TS 16W IS TRACKING NORTH-NORTHWESTWARD ALONG THE
WESTERN PERIPHERY OF A LOW- TO MID-LEVEL STEERING RIDGE.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 16W IS FORECAST TO TURN NORTHWESTWARD TO WEST-NORTHWESTWARD
IN THE NEXT 24 HOURS AS IT TRANSITIONS TO THE STEERING INFLUENCE OF
THE SUBTROPICAL RIDGE (STR) POSITIONED SOUTH OF JAPAN. DYNAMIC MODEL
GUIDANCE IS IN TIGHT AGREEMENT WITH A 120 NM SPREAD IN GUIDANCE AT
TAU 72. ADDITIONALLY, THE 20/00Z UPPER-AIR DATA FROM BOTH RJAO AND
ROMD INDICATE EAST-SOUTHEASTERLY FLOW IN THE MID-LEVELS, SUPPORTING
THE JTWC TRACK FORECAST. TS 16W IS EXPECTED TO INTENSIFY THROUGH THE
PERIOD UNDER FAVORABLE ENVIRONMENTAL CONDITIONS.
   C. AFTER TAU 72, TS 16W IS FORECAST TO TRACK SLIGHTLY MORE
POLEWARD AS THE SYSTEM TRACKS ALONG THE SOUTHWEST PERIPHERY OF THE
SUBTROPICAL RIDGE AND A MIDLATITUDE TROUGH DEEPENS OVER EASTERN
CHINA. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT WITH A 150 NM
SPREAD AT TAU 120 ALTHOUGH THERE ARE SIGNIFICANT DIFFERENCES IN
TRACK SPEED. ALTHOUGH THERE IS A FAIRLY TIGHT GROUPING OF MODEL
GUIDANCE, THE JTWC FORECAST FAVORS THE ECMWF AND JGSM MODELS, WHICH
ARE ON THE SOUTHERN EDGE OF THE AIDS ENVELOPE AND INDICATE A TRACK
SOUTH OF OKINAWA. THE BULK OF THE ENSEMBLE DATA ALSO SUPPORTS A
TRACK SOUTH OF OKINAWA. THERE IS HIGH CONFIDENCE IN THIS FORECAST
TRACK; HOWEVER, THERE IS ALSO A POSSIBILITY THAT THE SYSTEM COULD
TRACK CLOSER TO OKINAWA AS SUGGESTED BY NOGAPS, GFS AND UKMO.//
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