Heavy to very heavy rain is forecast nationwide from Sept 28-Oct 1 as tropical typhoon Noru moves from the South China Sea onto middle Vietnam on Wednesday.

At 4am on Monday, tropical typhoon Noru was over the middle of the South China Sea, with maximum winds of about 140 kilometres/hour.

The storm was moving west and expected to make landfall over the middle of Vietnam on Wednesday. Meanwhile, the southwest monsoon over the Andaman Sea, the whole of Thailand and the Gulf of Thailand is gaining strength.

Heavy to very heavy rain is forecast for the North, Northeast, Central including Bangkok and its vicinity, East and South regions from Sept 28-Oct 1.

During the period, waves in the Andaman Sea are expected to be 2-3 metres high, while in the Gulf of Thailand sea waves are expected to be 2m high.