Forecasters have warned of disruption to travel and power supplies across the region as winds could hit speeds of up to 70mph on Monday.
"An area of low pressure is expected to move eastwards across the UK on Monday with a swathe of very strong winds around its southern flank, which will cross much of southern England and parts of south Wales. The winds are likely to be very gusty at times, particularly in association with heavy showers running across these areas," the Met Office said.
In pictures: Storm Imogen's 100mph winds and 20m waves
A more severe amber weather warning has been issued for the south west coast of England on Monday, with winds of up to 80mph expected along the coast, particularly North Devon and Cornwall, forecasters warned.
The Environment Agency warned of an increased risk of flooding along the coast and some rivers in Devon, Cornwall, Dorset and Oxfordshire due to heavy rainfall.
"Storm Imogen will lead to large waves and spray along the south and south-west coastal parts of England on Sunday night and Monday," said the agency's duty flood risk manager Jonathan Day.
"We understand it is tempting to see the force of Mother Nature but people should take extreme care on coastal paths and not put themselves and rescue workers at risk. Please listen to the advice of the coastguard and the police about safe places to be. Flooding of low lying coastal roads is also possible and people should also avoid driving through flood water."
UPDATE: Travel delays
Southern, Southeastern, Gatwick Express, Thameslink and Great Northern trains are operating speed restrictions from 11am, Trains are running as advertised, but it warns passengers to check journeys ahead of time. Disruption is also expected later when winds pick up.
South West Trains said journeys could take as much as 30 minutes longer with speed restrictions between 11am and 3pm. Services on the Southampton to Weymouth route and also the Portsmouth to London via Haslemere and Guildford route are expected to be particularly affected. Coaches may also be running shorter.
Arriva and Great Western Railways are already operating speed restrictions and some services are already disrupted in Wales and the South West.
The latest travel updates for each service and more routes can be found at National Rail.