Tropical Storm SIX Advisory śro., 12.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 06W (SIX) WARNING NR
011//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 06W (SIX), LOCATED APPROXIMATELY 473 NM EAST
OF KADENA AB, OKINAWA, HAS TRACKED WEST-SOUTHWESTWARD AT 10 KNOTS (KTS)
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
REVEALS POCKETS OF CONVECTION OBSCURING A WELL-DEFINED LOW LEVEL
CIRCULATION CENTER (LLCC), LENDING GOOD CONFIDENCE TO THE INITIAL
POSITION. A 120102Z ASCAT-B IMAGE DEPICTS A SWATH OF 25-29 KT WIND BARBS
TO THE NORTH OF THE LLCC WITH WEAKER WINDS TO THE EAST AND SOUTH.
THEREFORE, THE INITIAL INTENSITY OF 25 KTS IS BASED ON THE
AFOREMENTIONED ASCAT AND DVORAK CURRENT INTENSITY ESTIMATES OF T1.5 (25
KTS) BY PGTW/RJTD WITH GOOD CONFIDENCE. PERSISTENT EASTERLY VERTICAL
WIND SHEAR (VWS) AND DRY AIR ENTRAINMENT SEEN IN TOTAL PRECIPITABLE
WATER IMAGERY OFFSET THE WARM (NEAR 30 CELSIUS) SEA SURFACE TEMPERATURES
AND EQUATORWARD OUTFLOW, PLACING TD 06W IN A MARGINALLY FAVORABLE
ENVIRONMENT. ADDITIONALLY, LOW 700-500MB RELATIVE HUMIDITY VALUES OF 40-
45% ARE CAUSING THE SYSTEM TO STRUGGLE. TD 06W IS TRACKING WEST-
SOUTHWESTWARD UNDER THE STEERING INFLUENCE OF A LOW LEVEL SUBTROPICAL
RIDGE (STR) ORIENTED WSW-ENE.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC
REASONING MESSAGE.
   B. DUE TO THE WSW-ENE ORIENTATION OF THE LOW-LEVEL STR, TD 06W IS
EXPECTED TO TRACK WEST-SOUTHWESTWARD THROUGH TAU 12 THEN TURN WESTWARD
AS IT APPROACHES THE RYUKYU ISLANDS. BY TAU 36, THE SYSTEM WILL SHIFT TO
A WEST-NORTHWESTWARD TRACK FOR THE REMAINDER OF THE FORECAST PERIOD.
OVERALL, TD 06W IS FORECAST TO TRANSIT THROUGH A MARGINALLY FAVORABLE
ENVIRONMENT OF LOW TO MODERATE EAST-NORTHEASTERLY VWS. COMBINED WITH
CONTINUED DRY AIR ENTRAINMENT AND LOW RELATIVE HUMIDITY VALUES, TD 06W
SHOULD REMAIN SHALLOW AND RELATIVELY WEAK WITH DISSIPATION EXPECTED BY
TAU 72, IF NOT SOONER. NUMERICAL MODELS REMAIN IN FAIR AGREEMENT WITH
CROSS-TRACK SPREAD INCREASING IN THE LATER TAUS AS THE SYSTEM
DISSIPATES. THE GFS ENSEMBLE REMAINS THE OUTLIER TO THE SOUTH AND IS
OFFSET BY THE NORTHERLY OUTLIER, NAVGEM. THUS, THE JTWC FORECAST TRACK
IS PLACED ALONG THE MULTI-MODEL CONSENSUS WITH MODERATE CONFIDENCE.//
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