FORECASTERS have warned Princess Eugenie's big day could be hit with rain today.

The ninth-in-line to the throne may be greeted with storm clouds as she arrives at Windsor to marry long-term boyfriend Jack Brooksbank.

Members of the royal family are expected to arrive at St George's chapel by 10.30am - with the Met Office predicting a 90 per cent chance of rain by 10am.

Becky Mitchell, a forecaster for the Met Office, told the Evening Standard: "They're just on the edge of where we're expecting rain to be. There's a chance of heavy bursts around 11am."

It comes as Storm Callum today hits the UK, sparking warnings of torrential rain, flooding and power outages around Wales.

Commuters have already been warned of travel chaos as trains and buses are cancelled, while some communities have been warned they could be cut off by flooded roads.

Luckily for the royal family, Windsor looks set to escape the worst of the storm.

She added: "Hopefully they will see some sunshine this afternoon.

"Hopefully the rain will happen when they're inside."

Guests arriving at the chapel this morning appeared extremely windswept as they headed inside.

The forecast hasn't stopped eager fans from lining the streets in Windsor ahead of the big day.

Danielle Lilley, 33, and Rachel Bruce, 47, tutors from Eugenie's boarding house at Marlborough, said they were looking forward to seeing familiar faces.

Ms Bruce said: "We're really excited and hoping we might see some of her friends from college.

"We're thrilled to be here."

Dinner lady Jacquie Rosser was in position early inside the castle grounds, hoping to catch a glimpse of pop star Robbie Williams.

The 46-year-old travelled from London with her daughter Poppy, 12, and 67-year-old mother Elizabeth Hayvall, from Sevenoaks in Kent.

Ms Rosser said there was a "lovely buzz about the place" following their overnight stay in Windsor.

Poppy, who said she was granted a day off school provided she agreed to tell the headmistress all about her day, told of her excitement at the ringside seat for the second royal wedding of the year.

She said: "It's amazing to come from watching it (the Duke and Duchess of Sussex's wedding) on the TV to actually being here and seeing what it's like."