Britain’s coldest May in more than 300 years will deliver 50mph gales, 5cm (2in) of rain and flooding.
Central England temperatures so far this month average 8.6C, 1.6C below normal.
The last time May was colder was in 1698, at 8.5C over the whole month.
And the Met Office has warned that weeks of wet weather ahead could wash out the Queen’s diamond jubilee celebrations.
The Environment Agency issued two flood warnings and 14 alerts, warning of high tides swamping coastlines across South Wales.
Up to 2cm of rain will fall across the south and Midlands today. Severe weather warnings have been issued in the south-west. Wednesday and Thursday will see many parts hit by another 3cm of rain – totalling 5cm, or a month’s worth, in 24 hours – with localised flooding and transport problems expected. Warnings have been issued.
Gales hitting 50mph will buffet vehicles, rip branches from trees and threaten property damage.
Deluges are being caused by 20C south-westerly winds colliding with near-freezing polar air. Significant temperature differences will spark downpours across the collision zone. Met Office forecaster Dan Williams said: ‘With ground already saturated, localised flooding is possible. After a drier weekend, next week is unsettled.
‘The May 22 to June 5 outlook, including the diamond jubilee, has no strong signal for a period of warm, dry weather.
‘We expect sunshine and showers during this period. Even though there’s a hint of warmer, drier weather, it is just a hint – and not much better than a 50-50 chance.’
The Queen’s diamond jubilee pageant faces a washout on tomorrow’s opening day at Windsor Castle.
Bookmakers William Hill offer 4/1 odds on a jubilee Monday washout. Travel association Abta has reported a rush of overseas jubilee weekend inquiries from Britons fearing another bank holiday washout.