Tropical Storm DOLPHIN Advisory lun, 11-05

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 07W (DOLPHIN) WARNING
NR 18//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 07W (DOLPHIN), LOCATED APPROXIMATELY 156 NM
NORTH-NORTHEAST OF POHNPEI, HAS TRACKED NORTH-NORTHWESTWARD AT 08
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS FLARING DEEP CENTRAL CONVECTION OVER A
PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER. A 102257Z METOP-A
MICROWAVE IMAGE REVEALS BROKEN CONVECTIVE BANDING WITH THE BULK OF
THE DEEP CONVECTION SLIGHTLY DISPLACED WESTWARD. THE CURRENT
POSITION IS BASED ON THE MSI AND THE AFOREMENTIONED METOP-A IMAGE
WITH GOOD CONFIDENCE. THE INITIAL INTENSITY OF 40 KNOTS IS BASED ON
A 102232Z ASCAT PASS SHOWING 35 TO 40 KNOT CIRCULATION AND HEDGED
SLIGHTLY HIGHER THAN DVORAK INTENSITY ESTIMATE OF 35 KNOTS FROM
PGTW. UPPER-LEVEL CONDITIONS REMAIN MARGINAL WITH EASTERLY DIFFLUENT
FLOW ALOFT AND MODERATE (20 TO 25 KNOTS) VERTICAL WIND SHEAR (VWS).
HOWEVER, SEA SURFACE TEMPERATURES ABOVE 29 CELSIUS REMAIN CONDUCIVE
FOR DEVELOPMENT. TS 07W IS TRACKING SLOWLY POLEWARD TOWARDS A BREAK
IN THE STEERING SUB-TROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE. HOWEVER, THE EXTENDED
TRACK FORECAST HAS POSITIONED SLIGHTLY SOUTHWARD DUE TO A CHANGE IN
AVAILABLE MODEL GUIDANCE. SEE PARA C FOR DETAILS.
   B. TS 07W WILL CONTINUE TO TRACK POLEWARD OVER THE NEXT 06 HOURS
AS AN UPPER-LEVEL TROUGH PASSES TO THE NORTH CAUSING A BREAK IN
THE STEERING STR. AFTERWARD, THE STR WILL REBUILD AND TURN TS 07W ON
A GENERALLY WESTWARD TRAJECTORY. UPPER-LEVEL CONDITIONS WILL REMAIN
MARGINAL OVER THE NEXT 48 HOURS LEADING TO A MODEST INTENSIFICATION.
BEYOND TAU 48, AN IMPROVING ENVIRONMENT, WITH LOW VWS (05 TO 10
KNOTS) AND AN INCREASING POLEWARD OUTFLOW CHANNEL WILL LEAD TO AN
INCREASED INTENSIFICATION RATE.
   C. AFTER TAU 72, TS DOLPHIN WILL TRACK WEST-NORTHWESTWARD  UNDER
THE STEERING INFLUENCE OF THE STR. BY TAU 96, ANOTHER APPROACHING
MID-LATITUDE TROUGH WILL CAUSE THE STEERING STR TO WEAKEN AGAIN,
ALLOWING TS 07W TO TURN SLIGHTLY POLEWARD TOWARDS A BREAK IN THE
STR. ENVIRONMENTAL CONDITIONS WILL REMAIN FAVORABLE AND SUPPORT
FURTHER INTENSIFICATION. NUMERICAL MODELS HAVE CHANGED OVER THE PAST
SIX HOURS, BUT OVERALL REMAINS IN GOOD AGREEMENT, INDICATING A
SOUTHWARD SHIFT IN THE TRACK DUE TO A BUILDING AFOREMENTIONED STR.
THEREFORE, THE EXTENDED JTWC TRACK FORECAST HAS POSITIONED SOUTHWARD
TO REFLECT THIS CHANGE. DUE TO UNCERTAINTY IN THE EXTENDED FORECAST
INTENSITY, THERE IS OVERALL LOW CONFIDENCE IN THE JTWC FORECAST.//
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