POLICE are warning people to watch out for road closures as the new session of Parliament meets.

Parliament is due to start at 10am on Wednesday and the State Opening is expected to last for two hours or more.

Forecasters have already predicted atrocious weather for the day including severe thunderstorms and flooding.

Road closures start from tonight (Tuesday) with Bay Street between Charlotte and East Streets including Rawson Square and Parliament Street closed to vehicular traffic from 9pm tonight.

There will be no parking in Bay Street between Charlotte and East Streets on both sides.

There will also be no parking on Parliament Street between between Woodes Rodgers Wharf, Shirley Street and both Rawson Square and Parliament Square.

Road closures: From 6am on Wednesday until after the ceremony, the following streets will be closed to vehicular traffic: Bay Street between Frederick and East Streets, Parliament Street between Shirley Street and Woodes Rodgers Wharf, Bank Lane between Shirley and Bay Streets.

No parking: From 6am on Wednesday there will be no parking until after the ceremony, on the following streets: Bay Street between Frederick and East Streets; East Street between Shirley Street and Woodes Rodgers Wharf; Woodes Rodgers Wharf between East and Frederick Street; Parliament Street between East Hill Street and Woodes Rodgers Wharf.

There is reserved parking between Shirley and Bay Streets.

Traffic diversions: From 6am on Wednesday vehicular traffic travelling east on Bay Street will be diverted north and south along Frederick Street.

Vehicular traffic wishing to continue east along Bay Street must travel east on Woodes Rodgers Wharf to East Street, south on East Street to Bay Street and east on Bay Street.