Today's hot weather is set to spark scattered thunderstorms later on Thursday, continuing overnight.
The Met Office has issued a yellow warning for thunderstorms. It says the spray and sudden flooding could lead to difficult driving conditions and some road closures.
"Where flooding or lightning strikes occur, there is a chance of delays and some cancellations to train and bus services," the Met Office reports.
"There is a chance that power cuts could occur and other services to some homes and businesses could be lost.
"There is a small chance that homes and businesses could be flooded, or damaged by lightning strikes, hail or sudden gusts of wind."
Temperatures are soaring on Thursday with sunshine and blue skies across Hemel Hempstead and beyond.
Forecasters say one or two intense thunderstorms are likely to break out in the Hemel area this evening and early tonight. It should become dry and clear later in the night though and expect another warm and humid night.
The warm temperatures remain tomorrow, but a touch cooler. It will be a dry to start to Friday but will become cloudier later with an increasing risk of showers or patchy rain.
Saturday and Sunday will see mostly cloudy skies with rain, some of which will be heavy and persistent with a rumble of thunder also possible.
Much cooler than earlier in the week. While Monday may continue to see a few showers, it should become drier with increasing spells of sunshine breaking though. Feeling warmer too.