The Met Office has issued a yellow weather warning after a week's worth of rain is expected to fall across Norfolk and Suffolk today.
There is also a small chance a month's worth of rain could fall across parts of the region, according to a weather expert.
The Met Office has said an area of heavy rain will move slowly southwards across the east and southeast of England today.
It said: 'Some transport routes may be affected by localised flooding leading to longer journey times. In addition, flooding of homes and businesses is possible. The heaviest of the rain should gradually become confined to the extreme southeast of the UK later in the day.'
Dan Holley, meterologist for Norwich-based Weatherquest, said the heavy rain started a few hours ago on the north Norfolk coast and was moving slowly down to the south of county.
He said: 'It is going to rain for most of the day.'
Mr Holley added between 10-15 millimetres of rain was expected to fall across Norfolk and Suffolk.
Some parts of eastern Suffolk could experience about 50 millimetres of rain today - just below the 56 millimetre average expected for the whole of August.
This could also be replicated in some localised areas of Norfolk, according to Mr Holley.
There might also be winds of between 40mph and 45mph along the north Norfolk coast.
He said: 'If you are on the north Norfolk coast it is going to be wet, rainy and windy.'
Temperatures are expected to be between 15 and 17 degrees Celcius - below the August average of 21-21 degrees Celcius.
Mr Holley added August was usually the third wettest month in East Anglia, behind October and November.
He said the weather should improve this week and the rain was expected to decrease after today going into the weekend.
'A little bit of rain is expected on Friday evening but during the weekend it should be pretty dry.'
Because of the rain, the National Trust has cancelled its Wild Wednesday family event today on Brancaster Beach, due to take place from 10.30am.
A post on Twitter from @BrancasterNT read: 'Due to today's inclement weather we have decided to cancel our Wild Wednesday event at Brancaster Beach. Sorry for any disappointment caused.'
Norfolk police is advising drivers to allow plenty of time for journeys as well as turning on vehicle lights if visibility is poor.
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