Train problems forecast along with more rain and flooding in the South of England
The weather has already affected several services
Train operators said more services could be cancelled as people across the south of England face further warnings of flooding, power cuts and road closures.
The Met Office issued a yellow weather warning from 12pm on Thursday with rainfall expected to travel in a north-east direction across the south of England, lasting until 3am on Friday.
It added there is a "small chance" that communities could become cut off by flooded roads.
The warning comes in the wake of Storm Henk that battered the UK on Tuesday and forced people to evacuate their homes, leaving one man dead from a tree falling in 90mph winds on the Isle of Wight.
The Met Office added that the spell of rain on Thursday was falling on already saturated ground which could cause "further flooding and travel disruption".
It said:
"The track of the heaviest rainfall remains very uncertain, but there is a chance of 20 to 30 millimetres falling in six to nine hours across a portion of the warning area, with a few places perhaps seeing 40 to 50 millimetres.
"Impacts are more likely due to the current very wet ground across the region."
Great Western Rail, which runs services westwards from London, said its trains from Swindon and Bristol Parkway remain closed due to flooding on the tracks during Storm Henk.
Trains are being diverted via Bath or Temple Meads potentially adding 40 minutes to passengers' journeys, it said.
The train operator said passengers could expect further disruption if high levels of rain return and urged anyone making journeys to south-west England to leave before 3pm.
In a statement, the firm said:
"With further flood warnings in place and the amount of rain forecast, Network Rail has identified key sites in Wiltshire, Somerset, Devon and Cornwall as being at risk of flooding from around 1500. Trains may not be able to operate through these areas."
Services between Paddington and Swindon will operate but may be affected by flooding elsewhere, the firm added.
GWR said customers with tickets for later services on Thursday could use them on earlier trains.
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