Heavy rain and thundery showers are predicted for the region over the weekend - including St Albans and Welwyn Hatfield.
The summer storms may lead to flooding and transport disruption in some places.
The Met Office has warned that there is a small chance that homes and businesses could be flooded, causing damage to some buildings.
Spray and flooding could lead to difficult driving conditions and some road closures, and a slight chance of power cuts and loss of other services to some homes and businesses.
Sunday will continue to be unsettled with heavy showery outbreaks of rain. However, there will be the odd sunny spell later in the afternoon. Monday will continue to see the odd spot of rain, but these will be lighter and more well-scattered.
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