Revellers flocking to Notting Hill Carnival in their hundreds of thousands have been warned to take umbrellas and waterproofs for a rainy edition of Europe's largest street festival.
Up to a million visitors are expected to descend on west London for the festivities, which officially get under way with Family Day today before the main parade on Bank Holiday Monday.
Led by members of the British West Indian community, the party features steel bands, flamboyant costumes, colourful floats, Calypso music, Caribbean food and 38 sound systems.
But forecasters have warned that showers and cool temperatures are expected to put a dampener on this year's proceedings.
Paul Mott, a forecaster at MeteoGroup, said: "Sunday will be a mostly cloudy day with an increasing risk of rain throughout the day and the best of the dry weather through the morning and the start of the afternoon.
"There could be a few heavy bursts of rain later in the afternoon and in the evening, so it's worth anyone going taking an umbrella or waterproofs, although it won't be cold with temperatures up to about 22C (71.6F).
"On Monday it's looking like quite a wet morning with fairly persistent rain and then maybe turning drier throughout the afternoon. It will be fairly cool, with temperatures of about 20C (68F) in Notting Hill."
Events kicked off last night with the free Panorama concert and steel band competition ahead of the Sunday Parade, which begins at 10am.
The atmosphere on Family Day is usually laid-back, with workshops and costume prizes, but the Bank Holiday Monday has a reputation for gang-related violence.
Police this week arrested dozens of people in dawn raids against potential troublemakers ahead of the street party.
About 1,000 officers from the Met and City of London police took part in the crackdown and recovered a firearm, quantities of drugs and cash.
They vowed to use specially-trained "super recognisers" to keep away those with bail conditions banning them from attending the event.
Superintendent Robyn Williams, Scotland Yard's spokeswoman for this year's celebrations, said: "We want visitors to come along and enjoy themselves whilst remaining safe.
"Unfortunately, given the large number of people the event attracts, there will always be a small number who see it as an opportunity to commit crime. My message to those who plan to cause trouble is do not come."
Organisers have come under fire this year for demanding that journalists and photographers covering the event pay £100 for accreditation and share their work for use on the carnival's website.
The accreditation form specifies that applicants must agree to "share their blog, video, article, write-up, recap, review or coverage of the events attended within three weeks of the conclusion of the event" which can be used on the carnival's own sites.
It also states foreign-language journalists must provide an English translation.
The National Union of Journalists urged journalists to reject the requirements, saying they could force some freelancers to operate at a loss.