The storm, which could bring gusts of up to 80mph, will hit on the morning of the royal wedding at St George’s Chapel in Windsor.
The Met Office has issued yellow weather warnings for Friday and Saturday and said to expect heavy and persistent rain which has the potential to cause flooding, “difficult” driving conditions and potential road closures.
Storm Callum is due to hit the UK just hours before the happy couple are expected to tie the knot in front of over 850 guests at 11am.
However the Met Office said on Wednesday the worst of the weather would be in western Scotland - where Camilla, Duchess of Cornwall will be visiting a school and therefore missing the celebrations - Wales and the Lake District.
Princess Eugenie and her fiancé Jack Brooksbank are expected to take part in a carriage ride around Windsor following their 11am church service, which will be broadcast live on ITV's This Morning.
Unlike Harry and Meghan's wedding earlier this year, a second day's celebration is also reportedly planned for Saturday, which has taken on a 'funfair theme'.
“After the more formal celebration at Windsor Castle [reportedly planned and overseen by Lady Elizabeth Anson, the Queen’s cousin], the Saturday bash will be a relaxed party” a source told The Telegraph.
“There will be dodgems and funfair rides, coconut shies, lots of food stalls, loads of cocktails, bloody Marys for the hangovers and a festival vibe.”
Buckingham Palace have released further details about the big day, announcing the bridesmaids and page boys who will make up the royal wedding party.
Among the little ones include Zara and Mike Tindall’s spirited four-year-old Mia and Peter and Autumn Phillips’ daughters Savannah and Isla.
Maud Windsor, who is Eugenie’s goddaughter and the daughter of Lord Frederick Windsor and his actress wife Sophie Winkleman, is also a bridesmaid.
The Duke and Duchess of Cambridge's son George will be joined by fellow page boy Louis de Givenchy – the six-year-old son of JP Morgan banking executive Olivier de Givenchy and his wife Zoe, their daughter Charlotte, 3, will be a bridesmaid.
Robbie and Ayda William's daughter Theodora, 6, will also be a bridesmaid, the couple having developed a close friendship with Eugenie and her mother Sarah Ferguson over recent years.
The Queen’s youngest grandchildren, 14-year-old Lady Louise Mountbatten-Windsor and 10-year-old Viscount Severn, who are the children of the Earl and Countess of Wessex, will take on the role of Special Attendants.
William and Kate’s youngest child Prince Louis, who is only five and a half months old, is too young to attend and will be staying at home.
Eugenie's sister Beatrice will be her maid of honour on the day, and Jack's brother Thomas will be best man.
It is not known yet if 97-year-old Prince Philip will attend the big day, with a royal source telling the Telegraph “He now very much operates on a “wake up and see how I feel” basis.”
Duchess of York Sarah Ferguson, who split from Andrew in 1992 but still lives under the same roof, is said to be “very nervous” about meeting Prince Philip, who has avoided her since her 1996 divorce.