LONDON  — Britain is bracing for hurricane- force winds and flooding starting this evening, with forecasters predicting the worst storm in five years will sweep across England and parts of Wales.

“We are confident that a severe storm will affect Britain on Sunday night and Monday,” Frank Saunders, chief forecaster for the U.K.’s Met Office, said in a statement late yesterday. “We’ll continue to work closely with authorities and emergency services to ensure they are aware of the expected conditions.”

The Met Office issued an alert for high winds in London, southern England, Wales, a large part of the Midlands and southeast. Wind speeds may exceed 80 mph in places and the storm has the potential to cause severe disruptions through falling trees, structural damage, transport and power failures and possible flooding, it said. London’s Heathrow Airport, Europe’s biggest aviation hub, expects an impact on flights beginning Monday morning.

The storm is “likely to cause disruption to flights at Heathrow including cancellations,” the airport said in an e- mailed statement today. “Passengers due to travel on Monday should check the status of their flight with their airline before traveling to the airport.”

The Met Office forecasts a low pressure system will rapidly deepen in the southwest of the country tonight.

The French national weather forecaster expects similar wind gusts to hit the Brittany and Channel coasts starting later today. It’s due to hit western France overnight before spreading to Normandy and Nord-Pas de Calais by Monday morning with gusts topping 80 miles per hour on the coasts, according to Meteo France.

South West Trains, a London commuter train operator, said yesterday that maintenance teams would visit sites across its network to prepare for the storm.

“The risk of falling trees as well as damage to buildings and equipment is high,” the company said in a statement on its website. “These conditions present risks to the railway from localized flooding, fallen trees and debris on the tracks.”

Sustained winds of 74-95 mph constitute a Category 1 hurricane on the five-step Saffir-Simpson scale.

The gusts may lead to shutdowns at turbines including those at the London Array, the world’s biggest offshore wind-power site, which automatically halt when wind speeds exceed 56 mph.

Gusts around the London Array are forecast at about 81 mph, Barrie Englishby, a production manager at the project in the sea east of London, said Oct. 25 in an e-mail. Structurally, the turbines and offshore sub-stations are designed to withstand conditions “far in excess” of those forecast, he said.

The storm, which has been named St. Jude after the patron saint of lost causes, whose feast day is tomorrow, has been developing over the Atlantic.

A strong jet stream and warm air close to the U.K. are contributing to its development and strength.

The amber alert covers London and South East England, South West England, Wales, the West Midlands and parts of the East Midlands, the Met said. A less serious yellow alert has been issued for Eastern England, the northeast and northwest.

Ferry services have been canceled today and tomorrow between Plymouth and Roscoff, in France, and between Penzance and the Isles of Scilly.

The U.K. Environment Agency warned the public to avoid seafronts, quaysides and jetties, while the Highways Agency said motorists should be aware of sudden gusts of wind and give high- sided vehicles, caravans, motorbikes and bicycles plenty of space.