WTJP21 RJTD 031800 WARNING 031800. WARNING VALID 041800. WARNING IS UPDATED EVERY 6 HOURS. TYPHOON WARNING. SEVERE TROPICAL STORM 2521 MATMO (2521) 990 HPA AT 17.6N 118.1E SOUTH CHINA SEA MOVING WEST 13 KNOTS. POSITION FAIR. MAX WINDS 50 KNOTS NEAR CENTER. RADIUS OF OVER 30 KNOT WINDS 210 MILES NORTH SEMICIRCLE AND 120 MILES ELSEWHERE. FORECAST POSITION FOR 040600UTC AT 18.5N 115.2E WITH 25 MILES RADIUS OF 70 PERCENT PROBABILITY CIRCLE. 980 HPA, MAX WINDS 60 KNOTS NEAR CENTER. FORECAST POSITION FOR 041800UTC AT 19.5N 112.5E WITH 35 MILES RADIUS OF 70 PERCENT PROBABILITY CIRCLE. 970 HPA, MAX WINDS 70 KNOTS NEAR CENTER. EXTENDED OUTLOOK. FORECAST POSITION FOR 051800UTC AT 21.8N 108.5E WITH 55 MILES RADIUS OF 70 PERCENT PROBABILITY CIRCLE. 980 HPA, MAX WINDS 55 KNOTS NEAR CENTER. FORECAST POSITION FOR 061800UTC AT 23.3N 104.6E WITH 80 MILES RADIUS OF 70 PERCENT PROBABILITY CIRCLE. 1004 HPA. BECOMING TROPICAL DEPRESSION. JAPAN METEOROLOGICAL AGENCY.=