Taiwan regularly gets hit by typhoons but they generally land along the mountainous and sparsely populated east coast facing the Pacific.
Krathon, categorised as a medium strength typhoon, is forecast to hit the major port city of Kaohsiung early on Wednesday, then work its way across the bottom tip of Taiwan and cross out into the Pacific, the Central Weather Administration (CWA) said on Monday.
The typhoon is expected to further intensify into the equivalent of a Category 4 hurricane, packing powerful winds of more than 220km/h near its centre, according to Tropical Storm Risk.
"The impact is getting bigger and bigger," said Gene Huang, forecaster at the CWA, pointing to threats to Taiwan's southwest and adding it was "rare" for such a powerful typhoon to make a direct hit to the island's western plains.
Huang warned residents there to be prepared for extreme winds of more than 150km/h.
Taiwan authorities said more than 1000 rubber boats and 2200 soldiers were on standby across Taiwan, including on the eastern coast where up to 1.3m of rain was expected in the coming days.
Boats to Taiwan's outlying islands have already been cancelled and some domestic flights have been disrupted.
In July, Typhoon Gaemi killed at least 11 people in Taiwan.Â
