Typhoon Sanba formed to the east of the Philippines, and quickly strengthened as it moved northwards.
Although the storm didn't make landfall in the Philippines, it intensified the monsoon rains across the country and caused widespread flooding.
The typhoon then treked northwards and in the early hours of Sunday made a direct hit on the Japanese island of Okinawa. Thousands are now without power and the torrential rain is still falling.
The storm is gradually weakening as it continues its journey northwards, but it is still expected to be the equivalent of a category one hurricane when it next makes landfall on the Korean Peninsula.
The south coast of South Korea is already seeing rain from the outer fringes of the typhoon, but the eye of the storm isn't expected to make landfall until 3 GMT on Monday.
This means there will be a prolonged period of intense rain, which will cause widespread flooding across much of North and South Korea.