Thunderstorms could bring flooding and travel disruption to the east of Wales on Thursday, forecasters have warned.
A yellow warning has been issued by the Met Office from 10:00 BST until midnight.
The forecaster said fast flowing or deep flood water was possible, potentially causing a danger to life.
Forecasters have also warned of potential delays and cancellations to bus and train services due to heavy rain and lightning strikes.
The warning covers 15 local authorities stretching from south to north.
They are Blaenau Gwent, Bridgend, Caerphilly, Cardiff, Denbighshire, Flintshire, Merthyr Tydfil, Monmouthshire, Neath Port Talbot, Newport, Powys, Rhondda Cynon Taf, Torfaen, Vale of Glamorgan and Wrexham.
Thunderstorms are likely to break out in some areas, particularly during the afternoon and early evening, with up to 40mm (1.5in) of rain expected to fall in parts in an hour.
Torrential downpours may be accompanied by frequent lightning, while wind and hail may also affect some places.