The Great South Run has been cancelled due to a forecast for “high winds and rain” – as well as a risk of “high tide levels” and “potential debris”.
More than 20,000 runners were expected to take part in Sunday’s event in Portsmouth.
Organisers said they had been monitoring the weather but it hadn’t improved enough for the event to be staged safely.
It comes as Storm Ashley is expected to hit parts of the UK on Sunday.
The storm, the first to be named this season, has been dubbed a “weather bomb” and could bring winds of 80mph.
Organisers of the run said the strong wind could “compromise our event infrastructure including our medical facilities”.
“This combined with high tide levels, potential debris, and the exposure along the seafront mean that we can’t guarantee the safe delivery of the event,” said a statement.
They said the decision hadn’t been taken lightly and was reached after liaising with the Met Office, medical and safety teams and local authorities.
The statement added: “We know how disappointing this is and we hope you can understand why this decision has been made.”
Storm Ashley is forecast to hit on Sunday. Pic: Met Office
Storm Ashley will bring high winds across the whole of the UK on Sunday and into Monday, according to the Met Office.
Conditions are expected to be worst in northwest Scotland, where an amber warning has been issued from 9am on Sunday until midnight.
A less serious yellow alert is in place from 3am Sunday until midnight over parts of west Wales, Northern Ireland, the whole of Scotland and Cumbria.
A further yellow warning for northern Scotland and the Hebrides is in force from midnight until 9am on Monday.
Sky News meteorologist Kirsty McCabe said Storm Ashley is “set to rapidly deepen on Saturday night”.
She said it would interact “with a very strong jet stream and undergo explosive cyclogenesis” – where the central pressure drops by at least 24 millibars in 24 hours, also referred to as a “weather bomb”.