The Environment Agency has put Sussex on flood alert for the rest of the week.
Higher than average tides are expected, coinciding with heavy rain which will see river levels rise.
Heavy rain and thunderstorms will last until Sunday as low pressure dominates the whole of southern England.
Because of the recent wet weather, rain will be falling on ground that is already saturated.
Problems are expected in estuaries prone to flooding where the high tides meet already swollen rivers.
Officials from the Environment Agency will be keeping an eye on the rivers Ouse, Arun, Adur and Rother as well as smaller rivers and brooks.
The agency may have to bring in its new flood warning system.
When officials believe flooding is likely it will issue a Floodwatch warning, where people are advised to listen to weather forecasts.
The next stage is when a Flood Warning is issued. People should take immediate action.
Pets and livestock should be moved, warm and waterproof clothing should be made available and residents should be ready to evacuate if necessary.
Then comes the Severe Flood Warning where there is imminent danger to life and property.
Under these circumstances the emergency services may begin to evacuate residents as it is expected their homes, businesses and caravans will shortly be flooded.
For further information about flood warnings call 0845 988 1188.
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