Homes have been flooded and emergency services are trying to rescue a group of campers as Storm Francis hits Wales.
Some roads are closed and motorists are facing widespread travel disruption as heavy rain caused river levels to rise.
Flood water has entered homes in south Wales, and firefighters are trying to rescue campers close to “fast flowing water” in Camartheshire.
The Met Office has warned injuries from “flying debris” are possible and large waves could endanger lives.
Properties have been flooded in Neath, Whitland, Tonyrefail and Llanelli.
It comes as the the Met Office said the UK was facing “another unseasonably wet and windy spell”, with some communities in Scotland warned they could be cut off by floods.
In Wales, commuters are also being warned of disruption, with roads closed and some trains cancelled or delayed due to the flooding.
National Rail tweeted that the railway line at Neath had been blocked, with trains between Swansea and Cardiff cancelled or delayed.
A 30mph speed limit has been put in place on a number of services in south Wales, with passengers warned to expect delays due to the severe weather.
Traffic Wales warned of “extremely poor driving conditions” and people should plan ahead.
In St Clears, emergency services are trying to rescue a group of campers from a campsite, close to a fast flowing river.
Firefighters and two rescue boats are at the scene of the rescue attempt, after the alarm was raised at just before 07:00 BST.
The yellow Met Office warning – telling people to be aware – is in place from 08:00 BST on Tuesday until 08:00 BST on Wednesday.
There could also be power cuts and buildings could be damaged as the wind spreads from the south west.
Three flood warnings have been issued along rivers in Carmarthenshire, with communities close to the River Hydfron at Llanddowror, River Gwendraeth Fawr at Pontyberem and River Gwendraeth Fawr at Pontyates and Ponthenry, told to be prepared.
There are also a number of flood alerts in place, including along the River Ely, Taf, Loughor and Amman, Llynfi and Ogmore, Nant-Y-Fendrod and Nant Bran.
A Met Office spokesman said: “Gusts are likely to reach 55-60 mph for quite a few places, with exposed coasts and hills seeing gusts of around 70 mph.”
A moderate rain warning has also been issued for Ceredigion, Conwy, Denbighshire, Flintshire, Gwynedd, Anglesey, Powys and Wrexham.
A Met Office spokesman said: “Heavy rain during Tuesday and early Wednesday is expected to result in some flooding and disruption to travel.”
It spans from 23:00 BST on Monday to 05:00 BST on Wednesday.