Floods in Wales were brought by an unusual front that moved from south to north, sucking in moist air from tropical Atlantic

A most extraordinary weekend of weather has just passed. The eastern side of the UK woke on Saturday to a stiff southerly wind and temperatures more akin to what can be expected in mid-August. By the afternoon, temperatures had widely risen to 25-26C across parts of the Wash and East Anglia.

Meanwhile, a rare type of frontal system further west brought severe flooding to parts of Wales as a river of tropical moisture fed heavy rains across the hills. Saturday’s rain band was unusual for the UK – a textbook weather front and its associated rain usually tracks from west to east across the country, driven on by westerly winds high in the atmosphere. Saturday’s front was different, as there was virtually no west to east progression. All the movement along the front was from south to north, feeding in warm, moist air from the tropical Atlantic. The strong southerly wind only served to intensify the rate at which the rain was falling.

Weatherwatch: The 'Pineapple express' flows from Hawaii to the US Read more

In the US, similar atmospheric rivers are notorious for causing severe flooding across Oregon, Washington State and California and are nicknamed the “Pineapple Express” thanks to the origin of their moisture being sourced to the pineapple groves of Hawaii.