The Met Office has warned of heavy rain tomorrow across south west Hertfordshire.
The yellow warning was issued yesterday - and warns of the possibility of localised flooding and disruption to transport.
The yellow 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 during the afternoon 50mm of rain may fall locally.
The warning is in place from 12pm tomorrow until 9pm.