WALES could see a month’s rainfall over the next two days as the hot humid air bursts into a torrential downpour, the Met Office has predicted.
Met Office forecasters say the heavy downpour will hit North and Mid Wales hardest, but other weather experts say the entire Welsh coastline is likely to be affected.
Average rainfall for June is around 86mm and forecasters say towns like Wrexham, Rhyl, Llandudno and Aberystwyth could be hit by flooding once the heavens open.
Parts of the UK including Belfast have already been hit by severe flash flooding this week, and Lampeter and Bangor have also seen flood problems.
In South Wales areas like Cardiff will see warm temperatures of 18C or 19C that will remain throughout today and tomorrow, but North Wales will be cooler with figures of around 15C-16C.
And forecasters say the wet weather is not likely to clear up until the weekend when it will give way to brighter and drier conditions.
Met Office forecaster John Hammond said, “There’s a chance we could see June’s average rainfall in Wales of 86mm and the weather shows a chance of localised flooding.
“The further north you go the greater the risk of more persistent rain on Thursday and into Friday.
“The North will be under slow-moving bands of rain and it will fall in just a couple of days.
“Northern locations like Rhyl, Llandudno and Wrexham will be affected, but it could go as far south as Cardigan Bay and Aberystwyth.”
Senior forecaster with Positive Weather Solutions, Jonathan Powell, said almost no part of Wales would escape the downpour, but the coastline would be worst affected.
“We expect the humidity to spark off thunder storms and torrential downpours. Over the last two days all the conditions have been right for this to happen.
“The cloud formations have not been there and not developed into the structures responsible for downpours.
“But we think time is running out and we’ll now see a breakdown from the humidity to much fresher conditions leading to the rainfall that will come on Thursday.”
Mr Powell, whose forecasting operation is based in Abergavenny, said in Northern Europe following periods of intense humidity the weather can become very unstable and result in heavy rainfall.
This occurs because two weather fronts like humidity and low pressure collide and a torrential downpour in one location often results.
It was such conflicting climatic conditions that led to 6cm of rain falling on Boscastle, in North Cornwall, over a two-hour period in August 2004. The same conditions brought flash flooding to parts of Anglesey this week.
Mr Powell suggested the high temperatures of 25C witnessed earlier in the week will drop down to 17C by the weekend.
He said today would produce the worst of the rainfall with up to 25mm to 40mm falling in coastal areas.
“The worst day for the rain will be Thursday – Friday is likely to produce a mixture of sunshine and showers.
“The coastal regions will cop the worst of it because the fronts are coming straight in off the sea.
“It will hit places like Pembrokeshire, Aberystwyth and Carmarthenshire and will take South Wales apart along the Bristol Channel and the Severn Estuary in Cardiff, Swansea and Bridgend.
“It will travel along the coastline – but all of us will have it and it will be more generalised than just in short bursts with between 25mm to 40mm at worst. Friday will be a lot fresher with a scattering of showers, but not on the same level as Thursday.”
A spokesperson for the Environment Agency said they have no flood warnings in place, but people should monitor the weather carefully.
“We’ve put contingencies in place if and when the rain drops down and causes a problem.
“Heavy rain is expected and we’re trying to work out which areas are the most vulnerable.
“But rivers don’t go up so quickly with heavy rain for short periods of time. Short rivers can rise quickly, but the main ones rise and fall very slowly. The Met Office have put out warnings and we would ask people to take heed of them.”