Tropical Storm USAGI Advisory mié, 21-11

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 33W (THIRTYTHREE)
WARNING NR 09//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 33W (THIRTYTHREE), LOCATED APPROXIMATELY 427
NM NORTHWEST OF SONSOROL, HAS TRACKED NORTHWESTWARD AT 04 KNOTS OVER
THE PAST SIX HOURS. THE INITIAL POSITION IS PLACED WITH FAIR
CONFIDENCE BASED ON ANIMATED MULTISPECTRAL SATELLITE IMAGERY WHICH
SHOWS AN ELONGATED, PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER
(LLCC) WITH DEEP CONVECTION SHEARED TO THE NORTHWEST. THE
ENVIRONMENT IS MARGINAL WITH GOOD EQUATORWARD AND POLEWARD OUTFLOW
CHANNELS AND WARM (28-29 CELSIUS) SEA SURFACE TEMPERATURE BEING
OFFSET BY MODERATE TO HIGH VERTICAL WIND SHEAR (20-25 KNOTS). TD 33W
IS TRACKING WESTWARD ALONG THE SOUTHERN EDGE OF A SUBTROPICAL RIDGE
(STR).
3. FORECAST REASONING.
   A.  THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. THROUGH TAU 72, TD 33W IS EXPECTED TO CONTINUE TRACKING
WESTWARD ALONG THE SOUTHERN PERIPHERY OF THE STR. THROUGH TAU 24,
MODERATE VWS AND LAND INTERACTION WILL MAINTAIN THE INTENSITY AT 30
KNOTS. AFTER TAU 24, TD 33W WILL TRACK OVER THE SULU SEA AND BEGIN
TO INTENSIFY SLOWLY TO A PEAK OF 55 KNOTS BY TAU 72. DYNAMIC MODEL
GUIDANCE IS IN GOOD AGREEMENT (TAU 72 SPREAD IS ABOUT 165 NM),
LENDING FAIR CONFIDENCE IN THIS PORTION OF THE JTWC TRACK FORECAST.
   C. AFTER TAU 72, TD 33W WILL BEGIN TO SLOWLY TURN POLEWARD AS IT
ROUNDS THE STR AXIS. DURING THIS PERIOD, THE TROPICAL CYCLONE WILL
WEAKEN DUE TO HIGH VWS AND LAND INTERACTION AFTER IT MAKES LANDFALL
OVER VIETNAM (ABOUT TAU 108). IN THE LATER TAUS, MODEL SPREAD GROWS
SIGNIFICANTLY AS DIFFERENCES IN THE ORIENTATION AND INTENSITY OF THE
STR CAUSE DIFFERENCES IN THE MODEL FORECAST TRACKS. THEREFORE, THERE
IS LOW CONFIDENCE IN THE JTWC TRACK FORECAST WHICH IS PLACED CLOSED
TO THE MODEL CONSENSUS.//
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