The Environment Agency says high groundwater levels mean a continued risk of flooding in many parts of Wiltshire and other areas including Hampshire, West Berkshire, West Sussex, Surrey and Kent.
Flood alerts and warnings for groundwater flooding are already in force and the forecast is for levels to continue to rise.
The A345 Salisbury Road is being described as just passable in Pewsey between the Swan Road junction and the Sharcott Drove junction because of flooding.
Floods at the A4361 in Broad Hinton at the Post Office Lane junction have now cleared but there is still flooding on the A4361 in Berwick Bassett at the turn for Berwick Bassett junction.
David Bedlington, flood risk manager, said: “Last night’s rainfall will have a significant impact on our rivers.
"With more to come over the weekend we are likely to see more flooding over the coming days.
“Our advice is to stay out of flood water and don’t try to drive through it – just 30cms can wash a car away.
“Environment Agency teams continue to work around the clock to prepare for the rainfall by operating pumping stations, issuing flood warnings and checking that flood banks, walls, and barriers are all working effectively.
"We are ready to deploy pumps to affected areas and our staff remain out in communities affected by flooding.
“We will continue to monitor the situation very closely, but we want to remind people that we cannot prevent flooding and we urge communities to be aware of their risk and be ready to act.”
Communities are urged to sign up for free flood warnings and to take action if they receive one.
Advice and guidance about flooding is available on the Environment Agency website and from the floodline on 0845 988 1188.
Follow the Environment Agency on Twitter @EnvAgencySW and @EnvAgencySE