The Met Office has upgraded its wet weather warning to amber in the south of the Anglia region with a yellow warning elsewhere.
It says: "Flooding and transport disruption likely from heavy rain in southeast England during Monday afternoon and evening."
There could be up to 60 mm (2.4 inches) rainfall in a few places.
The normal average rainfall total for the whole of June in the Anglia region is 54 mm.
The amber warning is in effect from 3pm until 11pm on Monday.The yellow warning is effect until midnight on Monday although it will continue in the north west of the Anglia region into Tuesday
What to expect
Homes and businesses are likely to be flooded, causing damage to some buildings
Delays and some cancellations to train and bus services are likely with spray and flooding probably leading to difficult driving conditions and some road closures
Fast flowing floodwater is possible, causing danger to life
Power cuts and loss of other services to some homes and businesses likely
What does an amber warning mean?
There are three levels of weather warning - yellow, amber and red. A red alert is very rare.
An amber warning means there is an increased likelihood of impacts from severe weather, which could potentially disrupt your plans.
This means there is the possibility of travel delays, road and rail closures, power cuts and the potential risk to life and property.
You should think about changing your plans and taking action to protect yourself and your property.
You may want to consider the impact of the weather on your family and your community and whether there is anything you need to do ahead of the severe weather to minimise the impact.