The system is currently located around 300 kilometres to the southeast of the capital Taipei and is packing winds of around 160 kilometres per hour, with gusts close to 195 kilometres per hour
The usual heavy seas and storm surge are expected in the coming hours.
The Joint Typhoon Warning Center has forecast a maximum wave height of up to 10 metres.
Nesat is not expected to strengthen much further because the outer bands of the storm are now hitting the east coast. In fact, by the end of the day, those are likely to be 120 kilometres per hour.
The accompanying rain, however, will be of much greater significance.
Orchid Island, just to the southeast of Taiwan, recorded 117mm on Friday. Some parts of Taiwan are likely to see around twice that amount over the next 24 to 72 hours.
There have already been some staggering rainfall totals across southern Taiwan. Pingtung County has been particularly badly hit. Chunri Township recorded 222mm in 24 hours up to 2:00pm local time.
Meanwhile, Jiadong Township notched up 255mm. The heaviest rainfall was registered in Xinpi County where 265mm fell during the same period.
The mountainous central region could receive more than 300mm of rain as the typhoon slowly drifts across the area. Rainfall totals are being enhanced by a nearby tropical depression.
Tropical Storm Haitang
Tropical Storm Haitang is currently 500km to the southeast of Hong Kong.
The storm caused some flooding in the northwestern Philippines.
It is a weakening feature in terms of the winds, but as it makes its way due north, it will drag warm, moist air towards the southeast of China and across the Taiwan Strait.
The two systems are moving close enough together to merge into one large mass of heavy and steady rain.
Some parts of southeast China and Taiwan could see four or five days of torrential rainfall.
Widespread and life-threatening flash floods are highly likely.