Brighton Pride starts today (Saturday 3 August) with thousands already gathering in Madeira Drive on the seafront for the parade.
Tens of thousands of people are expected to take part in the parade and line the route via West Street, North Street and London Road to Preston Park.
Alison Moyet, Paloma Faith, Ms Dynamite and the original Sugababes – now known as MKS – are due to perform in the park today.
This year is the 40th anniversary of Brighton Pride which first took place in a much less gay-friendly era.
Those attending the weekend-long celebration, which centres on the St James’s Street area later, can expect dry weather, sunshine and temperatures of up to 70F or 21C.
The parade is expected to include about 50 floats. It is due to set off from Madeira Drive, heading west along the seafront, at 11am. The tail end of the parade should reach Preston Park by about 2pm.
Brighton and Hove Buses said that several of its services would be affected by the road closures between 10am and 2.45pm.
The company said that it hoped to restore services in the Old Steine area from about 12.30pm and in and around London Road and the Open Market from about 1pm.
The train operator Southern said that Preston Park Station would be closed all day. The company said that people coming by train to Pride should use Brighton Station where the large crowds expected would be marshalled.
Sussex Police said that three suspected drug dealers were arrested in the run up to today’s event.
Detective Chief Inspector Paul Betts said: “Pride is a fantastic community event and is great for the city, attracting around 160,000 people who come to enjoy a weekend of festivities.
“Sussex Police works closely with the Pride organisers in order to make sure the event remains as safe as possible for everyone.
“However, as with many large-scale events, there is always a minority who will look to exploit the situation by making money dealing in illegal substances.
“In order to tackle this we will always increase drug enforcement activity leading up to an event like Pride.”