Heavy, persistent rain on Saturday and Sunday is likely to bring significant river and surface water flooding to parts of England over the weekend.
Those who have tickets for the Spectacle of Light on Saturday can use their tickets on any of the other dates which run until February 23.
While Storm Dennis is not predicted to be as severe as Ciara, wet and windy conditions are expected to continue until Tuesday.
Storm Dennis will bring some unsettled weather to Sussex this weekend, the Met Office has said.
Media captionBBC Weather's Tomasz Schafernaker looks at the areas most likely to see severe impacts from Storm Dennis.
Paul Davis, principal meteorologist at the Met Office, said: "With Ciara the rain was heavy but swift".
An easyJet spokesperson said: "We are doing everything possible to minimise the impact of the disruption for our customers and to arrange alternative travel".
Network Rail is also advising passengers to expect delays and cancellations to services due to flooding, and to allow more time for their journeys.
Heavy rainfall is expected from 6pm today (Friday).
Curtin said about a quarter of the agency's 400 river gauges - used to measure water levels - have broken their highest-ever record in the past 10 years.
An amber alert for rain covers parts of Dumfries and Galloway and the Borders from 12:00 to 23:00 on Saturday.
Storm Dennis' arrival on Sunday has prompted another yellow warning until noon on Monday, for winds gusting to 70mph, affecting the whole of Scotland apart from Orkney and Shetland.