The Met Office has issued a yellow "be aware" warning of heavy rain in South Wales.
It says 15mm to 25mm could fall in six hours and up to 40mm on high ground.
The areas affected: Swansea, Bridgend, Neath Port Talbot, Vale of Glamorgan, Rhonnda Cynon Taff, Cardiff, Caerphilly, Merthyr Tydfil.
The Met Office says there is a risk of localised flooding.
There's a "be aware" warning from the Met office of heavy rain for the whole of Wales.
Forecasters say there could be locally torrential downpours in places.
Localised flooding's also a possibility.
There is rain, surface water and reduced visibility on the M4 between J30 A4232 (Cardiff Gate) and J23 M48.
The Met Office has issued a yellow "be aware" warning of rain for parts of Denbighshire, Flintshire, Wrexham, Conwy, Gwynedd and Powys.
It says up to 4cm is possible.
Rain will continue for the next few hours and we could still see some heavy downpours. Accumulations of 20-40 mm are likely.
The MET Office has issued a yellow weather warning because of the risk of surface water flooding. The warning is valid until 1600.
Rain will slowly clear eastwards later in the afternoon, perhaps allowing some brightness to develop. Rather windy, especially on coasts and hills. Maximum temperature 20 °C.
There are hazardous driving conditions because of rain, reduced visibility and surface water on the M4 between J23 (M48) and (J38) Margam.
Forecasters say up to 4cm of rain could fall across Wales in the hours to 4pm.
They say there's a risk of surface water flooding.
The Met Office has issued a heavy rain warning for:
Carmarthenshire, Merthyr Tydfil, Monmouthshire, Neath Port Talbot, Powys, Rhonnda Cynon Taff, Swansea, Blaenau Gwent, Bridgend, Caerphilly, Torfaen, Cardiff, Newport, Vale of Glamorgan, Ceredigion, Pembrokeshire, Wrexham, Denbighshire and Gwynedd
The Met Office says surface water flooding is likely on stretches of the road network, and in places strong winds will lead to considerable spray.