Rihanna may need an umbrella for headline slot at Radio 1's Hackney Weekend this evening

Rihanna could find herself feeling a bit chilly if she sports her usual risqué attire (Getty)

Umbrella singer Rihanna may well need her brolly today when she takes to the stage to headline at Radio 1's Hackney Weekend.

The chart star - who was yesterday reunited with her mentor Jay-Z - is set to top the bill at the east London music festival, which will also see performances from Plan B, Florence + The Machine and a mystery special guest.

Forecasts suggest many of the acts - including Tinie Tempah, Jessie J and Professor Green - will find themselves singing in the rain.

But fans are unlikely to be discouraged by the wet weather, with some 50,000 expected to descend on the site.

A similar number turned out yesterday to watch US hip-hop star Jay-Z close the day's event.

Earlier, his protege put in a surprise appearance and the pair performed their hit Run This Town, to the delight of crowds.

Talk That Talk singer Jay-Z - real name Shawn Carter - topped the star-studded bill at the Hackney marshes, where other star performers included American musicians Nicki Minaj, Will.i.am and Jack White as well as home-grown talent such as Leona Lewis, Example, Rizzle Kicks, Ed Sheeran and Michael Kiwanuka.

Lewis, who grew up in Hackney, spoke of her pride at performing on her home ground to open the BBC's biggest free live event.

The X Factor winner said backstage: "I really wanted to open when they asked me to do it.

"When I went on I saw 30,000 people running towards the stage.

"It was lovely performing in front of a home crowd. It was good, I swear half the audience was my friends and family."

Away from the main stage, today's performers include Lana Del Rey, David Guetta, Zane Lowe, Chase and Status, Nas, Wretch 32, Taio Cruz and Santigold.

PA