Joan then entered the South China Sea. However, its path over Luzon had caused it to lose organisation around the vertical structure of the central eye region of Joan. Over October 14 and 15, the area of gale-force (tropical storm-force) winds grew to a - (400 km) radius from its centre. Its eye diameter also grew to 80 miles (130 km) - double the average eye diameter. This area filled almost the whole northern South China Sea and made Joan the largest storm of the season in size.