People are being warned to expect disruption with short-term power outages and some localised flooding "likely" as thunderstorms are set to hit much of Wales.
The Met Office says most of south-east, mid and parts of north-east Wales will see stormy weather from Monday (5 September) afternoon through to the early hours of Tuesday.
Disruption on the roads, power cuts and flooding of homes and businesses could happen as a result.
Motorists and other road users are advised to take care and allow extra time for their journeys. Delays to train services are also "likely", according to the Met Office.
It follows another night of thunderstorms on Sunday (4 September) where wet weather covered large parts of the country.
Rain is not expected to amount to much more than some isolated, scattered showers on Monday until the later afternoon.
Then heavier bands of rain are due to move in from the west and south of the country, travelling north-east.
Conditions will clear on Tuesday morning for a dry start for most but more rain is in the forecast for that afternoon, with a risk of hail in some areas.
The Met Office warns that the rest of the week up to Saturday will see the "unsettled" weather continue, with more rain and thunder predicted.
Met Office spokesperson Oli Claydon said: “The main factor leading our weather in the next few days and indeed through the week is an area of low pressure that’s coming to the west of the UK.
"And it sits there through the week very slowly moving eastward.
“From that area of low pressure we’ll get a number of fronts that are sort of spinning off it, as well as the thunderstorms which are being pushed up from the south.
“We’ve also got a cold front that’s moving eastward off of that low pressure, bringing further rain as well."
He added: “Compared to the weather that we’ve had throughout the summer, with prolonged dry conditions and high pressure, it is very much a change in weather type as we’ve moved into autumn."