The Met Office has issued a heavy rain warning today for the area covering south west Hertfordshire.
The yellow warning warns of the possibility of localised flooding and disruption to transport.
The alert is the lowest level of severe weather warning and asks members of the public to "be prepared for adverse weather".
The Met Office’s chief forecaster said locally 15-20mm of rain is possible in an hour.
The warning is in place until 7pm tonight.
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