THUNDERSTORM warnings forced officials to cancel all but one race in Sai Kung, handing Sam Wong Tak-sum victory in the third leg of the Mobil Hong Kong circuit yesterday at Sha Ha Beach. Race officer Lee Lai-shan, the world, Asian and European women's champion, called off the morning race because of yesterday's severe rains. Wong won the only race of the day to comfortably take the title following his three wins on Saturday. Ken Wong Hop-hei, who was beaten by Sam Wong for a place in Hong Kong's team for October's Asian Games in Hiroshima, was second overall ahead of Tang Luen-chun. Asian Championship runner-up Wong, who with Lee leaves for Winnipeg, Canada this week for the world championships, said he felt better in yesterday's one race than throughout Saturday's competition. ''I think I performed much better than I did on the first day,'' said Wong. ''My target is the world championships and this result helps my confidence. ''It's going to be new ground for us in Winnipeg because it is the first time we sail on a lake.'' Lee, recently chosen as Hong Kong Sports Institute Athlete of the Year will be defending her world title in Winnipeg. Meanwhile, host team Kowloon Fleet were surprisingly beaten for the team award by Tai Po. Kowloon Fleet captured all six team awards last season.