Tropical Storm BOLAVEN Advisory Sa, 21.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (BOLAVEN) WARNING
NR 04//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 16W (BOLAVEN), LOCATED APPROXIMATELY 410 NM
SOUTH OF IWO TO, JAPAN, HAS TRACKED WEST-NORTHWESTWARD AT 03 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY DEPICTS A MORE TIGHTLY WRAPPED LOW-LEVEL CIRCULATION CENTER
(LLCC). A 201741Z SSMI 89GHZ IMAGE DEPICTS THE DEEP CONVECTION IS
STILL MOSTLY CONFINED TO THE SOUTHERN SEMI-CIRCLE AND A 1729Z TRMM
37GHZ IMAGE STILL DEPICTS A TIGHTLY WRAPPED LLCC WITH SHALLOW
CONVECTIVE BANDING. THE INITIAL INTENSITY OF 45 KNOTS IS BASED ON
DVORAK ESTIMATES OF 45 KNOTS FROM ALL AGENCIES (PGTW,KNES, AND
RJTD). THE INITIAL POSITION IS BASED ON RECENT EIR ANIMATION AS
WELL AS THE AFOREMENTIONED IMAGERY WITH FAIR CONFIDENCE. UPPER-
LEVEL ANALYSIS CONTINUES TO SHOW A FAVORABLE ENVIRONMENT WITH
IMPROVED RADIAL OUTFLOW, ALTHOUGH THE OUTFLOW CHANNEL INTO THE TUTT
TO THE NORTHEST HAS WEAKENED AS THE TUTT HAS FILLED. TS 16W IS
SLOWLY TRACKING WEST-NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY
OF A LOW- TO MID-LEVEL SUBTROPICAL STEERING RIDGE TO THE NORTHEAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 16W IS FORECAST TO CONTINUE WEST-NORTHWESTWARD AND PICK UP
SPEED IN THE NEXT 24 HOURS AS THE SUBTROPICAL RIDGE (STR) SOUTH OF
JAPAN AMPLIFIES AND BECOMES THE DOMINANT STEERING INFLUENCE WHILE A
LONGWAVE TROUGH THAT IS CURRENTLY OVER CHINA WEAKENS AND MOVES OUT.
DYNAMIC MODEL GUIDANCE IS IN FAIRLY TIGHT AGREEMENT WITH NGPS AND
GFDN SHOWING A SLOWER MORE SOUTHERN TRACK WHICH SEEMS UNLIKELY DUE
TO THE STR ALREADY WELL-ESTABLISHED AS SUPPORTED BY UPPER AIR
OBSERVATIONS IN THE REGION. TS 16W WILL CONTINUE TO INTENSIFY AS
ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE.
   C. AFTER TAU 72, TS 16W IS FORECAST TO CONTINUE TO TRACK WEST-
NORTHWESTWARD BUT SHOULD SLOW AS ANOTHER MIDLATITUDE TROUGH DIGS IN
FROM EASTERN CHINA, WEAKENING THE STEERING STR. DYNAMIC MODEL
GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 72 WITH THE SIGNIFICANT
DIFFERENCES BEING IN TRACK SPEED WHICH MAY AFFECT THE INTENSITY.
AFTER TAU 72, THERE IS A SPREAD OF MODELS WITH NGPS AND GFDN
SHOWING A SLOWDOWN AS THE SYSTEM INTERACTS WITH THE AFOREMENTIONED
MIDLATITUDE TROUGH AND A POSSIBLE NORTHERLY TURN WHILE GFS, JGSM,
AND EGRR SHOW A FASTER TRACK NORTHWESTWARD WITH NO WEAKENING OF THE
SUBTROPICAL RIDGE. THERE IS HIGH CONFIDENCE UP TO TAU 72, BUT
AFTERWARDS, THE CONFIDENCE IS LOW DUE TO THE TIMING AND EFFECT OF
THE MIDLATITUDE TROUGH ON THE STR.//
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