By Shelley Shan / Staff reporter
Heavy rain yesterday killed a motorcyclist in Kaohsiung and forced the Tainan City Government to cancel work and classes.
The heavy rains that affected central and southern Taiwan were triggered by a southwesterly wind interacting with a convection circulation.
The Pingtung County Government closed schools and offices in Chunrih Township （春日） due to road damage.
TV news footage showed Tainan residents pushing motorcycles through the floodwaters. In Rende District （仁德）, which was severely affected, police on patrol waded through floodwaters instead of riding scooters.
Some people tried in vain to salvage their vehicles.
“When I came downstairs, my car was already deep in water. It all happened in 20 minutes,” a man told a TV news reporter.
A man in Tainan’s Yongkang District （永康） said that yesterday’s rain was worse than the flooding during Typhoon Morakot in August 2009, a storm that killed 619 people.
Central Weather Bureau statistics showed that at 325.5mm Tainan received the most rain from 12am to 4pm. Pingtung followed with 279mm and Kaohsiung with 269.5mm, while two or three observation stations south of Taichung recorded rain that exceeded 100mm per hour.
Tainan nearly had torrential rain, which is 350mm of rain accumulated within 24 hours. Pingtung and Kaohsiung had extremely heavy rain, which the bureau classifies as 200mm of rain in 24 hours.
The interaction of high humidity, the southwesterly wind and convection circulation at 12am contributed to the extremely heavy rain that happened in such a short period of time, bureau forecaster Chen Yi-hsiu （陳依秀） said.
Taiwan is in a zone of low pressure, in which the southwesterly wind is the dominant force, stretching from Japan and South Korea to the Philippines and the South China Sea, Chen said, adding that the nation would experience the effects of the southwesterly wind until Sunday.
Rain is expected again in central and southern Taiwan early this morning, but it would not be as strong as yesterday, she said.
From tomorrow to Friday, the wind is expected to strengthen due to Typhoon Krosa, which is forecast to move toward Japan and South Korea today and tomorrow, she said, adding that rain is forecast from tomorrow afternoon through Friday night.
Although the possibility of torrential rain is not excluded, heavy to extremely heavy rain is forecast for central and southern Taiwan before Sunday, Chen said.
Former bureau Weather Forecast Center director Daniel Wu （吳德榮） said that the atmosphere within the monsoon trough is more unstable than the one during the plum rain season.
Its ability to trigger severe weather — including thunder and lightning, strong wind, heavy precipitation, tornadoes and consecutive heavy rain — is similar to that of the plum rain season, he added.
The southwesterly wind was produced by Tropical Depression Lekima, Weatherrisk Explore chief executive officer Peng Chi-ming （彭啟明） said.
“Typhoon Krosa’s development has strengthened the southwest monsoon, which in turn increased humidity near Taiwan and made meteorological conditions unstable along the central and southwest coasts, worsening the chances of convections, lightning and tornadoes,” Peng said.
Vice Premier Chen Chi-mai, center, visits a flooded area in Tainan yesterday. Photo: Wan Yu-chen, Taipei Times
A car purchased two months ago is submerged in floodwater in Tainan yesterday. Photo: Wang Chieh, Taipei Times