Much of Wales is expected to be battered by strong winds and heavy rain as Storm Dennis arrives on Saturday.
Up to 120mm of rain could fall, with flooding likely in some parts, causing travel disruption.
A Met Office amber warning for rain, meaning there is an increased likelihood of severe weather, covers 16 local authority areas.
There is also a yellow “be prepared” warning of gusts up to 70mph covering the whole of Wales.
The Met Office warned of the possibility of homes and businesses being flooded, dangerous fast-flowing waters, difficult driving conditions, communities being cut-off and power losses.
It comes after Storm Ciara caused disruption last weekend.
Where and when will Storm Dennis hit?
An amber warning predicting severe rain is in place from 12:00 GMT on Saturday until 15:00 on Sunday.
Of the 22 Welsh local authority areas, 16 are covered, with up to 40mm widely expected to fall and up to 120mm on higher ground.
Those affected are Blaenau Gwent, Bridgend, Caerphilly, Carmarthenshire, Ceredigion, Conwy, Denbighshire, Gwynedd, Merthyr Tydfil, Monmouthshire, Neath Port Talbot, Newport, Powys, Rhondda Cynon Taf, Torfaen and Wrexham.
The yellow warning for strong winds is in place from 10:00 GMT on Saturday until 12:00 Sunday and covers all of the local authority areas.
The Met Office has warned of some delays to road, rail and ferry transport, while coastal communities could also be affected by spray or large waves.
Natural Resources Wales (NRW) said there was “potential for significant impacts across Wales”.
“We expect the worst of the rain on Saturday afternoon and overnight into Sunday,” said Jeremy Parr, NRW’s head of flood and incident risk management.
There is one flood warning in place on the lower Dee valley in Llangollen and Wrexham, with alerts for the north Wales coast, west Anglesey, and Ceredigion.
What if I am travelling?
Ferry crossings between Pembroke and Rosslare on Saturday have been cancelled by both Irish Ferries and Stena Line.
Flybe, which operates a large number of flights out of Cardiff Airport, has not cancelled any flights but said it has “minimum acceptable weather conditions” it can operate in.
A spokesman said anybody booked on flights over the weekend can rebook to fly another time.
Heathrow, Gatwick and Bristol airports are also among those affected due to cancellations by British Airways and easyJet.
Transport for Wales (TfW) and Network Rail are still clearing up after Storm Ciara. Buses have replaced trains in Conwy Valley, on the Cambrian Coast and between Aberystwyth and Machynlleth.
TfW has made alterations to a large number of routes for the weekend and Monday, with some stops on journeys being missed out.
Those affected include Birmingham to Aberystwyth, Cardiff to Holyhead, and Manchester to Carmarthen, with full details online.
On the roads, flooding has been causing hold-ups on the A55 at Northop, Flintshire.
And in Monmouthshire, the M48 Severn Bridge is closed eastbound for traffic heading into England, with diversions in place.
How have people prepared?
On Anglesey, flood defences were erected at the council’s headquarters on Friday evening.
In Bridgend, drains and culverts have been cleared to reduce the risk of flooding, while Blaenau Gwent council is carrying out “precautionary work in identified problem areas”.
Floodgates are closed at Deganwy, Llanfairfechan, Kinmel Bay and Llanddulas, in Conwy county.
The National Botanic Garden in Carmarthenshire is closed on Saturday because of the forecast.
Pembrokeshire council is not expecting the “really severe weather” that led to it closing the A487 at Newgale, the Cleddau Bridge and ferry ports of Pembroke Dock and Fishguard last week.
However, a spokesman said the Cleddau Bridge may have to shut to high-sided vehicles if winds get too strong.
In Caerphilly, the local authority warned trees and structures may have been weakened by Storm Ciara and already saturated ground may cause localised flooding.