Storm Dennis[a] was a European windstorm which, in February 2020, became one of the most intense extratropical cyclones ever recorded, reaching a minimum central pressure of 920 millibars (27.17 inches of mercury).

After bringing blizzard conditions to the Midwest and heavy snowfall to New England, the cyclone emerged into the north Atlantic, where it redeveloped into Storm Dennis, officially named by the Met Office on 11 February – Dennis subsequently underwent explosive cyclogenesis on 13 February, reaching its near-record low pressure south of Iceland the following day.

Destructive winds and heavy rainfall moved south into the British Isles over the weekend of 15–16 February as Dennis passed north of Scotland; the storm subsequently began to weaken, making landfall in Norway the following day.

[3] By 15 February, as Dennis stalled to the south of Iceland, it had a near-record central low pressure of 920 mb (27 inHg) and winds gusting up to 140 mph (230 km/h) offshore.

[7] The warning covered the Welsh capital, Cardiff, and eight surrounding council areas: Blaenau Gwent, Bridgend, Caerphilly, Merthyr Tydfil, Neath Port Talbot, southern Powys, Rhondda Cynon Taf and Torfaen.

In the UK, two people were killed on 15 February: a man was found dead hours after falling overboard from a tanker and a teenager died after entering the sea in Kent.

[9][10] The UK Met Office issued a red weather warning, meaning "danger to life", for prolonged periods of heavy rain in south Wales on 16 February until 11:00 GMT, covering nine council areas including Neath Port Talbot.

[16] Met Éireann issued a total of six yellow and orange wind and rain warnings spanning from Saturday morning until the early hours of Monday.

At the peak, a status orange wind warning was active between 10am and 10pm Sunday for nine counties: Donegal, Leitrim, Sligo, Mayo, Galway, Clare, Limerick, Kerry and Cork.

[26] Labour shadow environment secretary Luke Pollard criticised Prime Minister Boris Johnson for being absent from areas flooded by Ciara and Dennis and for his failure to convene an emergency Cobra meeting in response to the crisis.