© Niall Carson/PAWaves in Dublin Bay as storms batter Ireland and the UK.
The wave was measured at a special buoy off the Donegal coast on Tuesday as a force ten storm raged.
Meteorologists at Met Eireann said the data, sent from about 60 miles from the Irish coast, provided evidence of the most severe weather conditions it has encountered that distance offshore.
"At 14.00 today the M4 weather buoy off the Donegal coast recorded a maximum wave height of 20.4 metres which is the highest maximum wave recorded in Irish waters," Met Eireann reported.
At Malin Head, the most northerly tip of Ireland, wind gusting to 87mph (140km/h) was recorded.
Elsewhere, the Irish coastguard has urged people to stay off exposed coasts, cliffs, piers, harbour walls, beaches and promenades during this week's forecast stormy weather.
Winds and stormy conditions will ease on Tuesday night before freezing conditions hit Ireland on Thursday and there is a risk of a second storm hitting the south and midlands. Forecasters, however, said there was a chance the storm might miss Ireland to the south.
The Weather Buoy project is a collaborative initiative between the Department of Transport, Marine Institute, Met Eireann and the UK Met Office.
The manager of the Irish coastguard, Declan Geoghegan, said: "The combination of tides, forecasted gale warnings for the next day or so, high sea conditions and swollen rivers may result in very dangerous conditions."
Much of the UK also faces several days of battering winds and localised blizzards as a pair of particularly lively weather systems pass over the country in quick succession.
Later on Tuesday gales were expected to batter the north of Northern Ireland and the west of Scotland, peaking at 80mph in coastal areas, where ferry services in the west of Scotland have been badly affected. This will be combined with driving rain and, on higher ground, reasonably heavy snowfalls, mainly in the Borders and in Dumfries and Galloway.
Conditions should ease during Wednesday and early Thursday, but only before another stormy weather system arrives, currently massing over the Atlantic.
It might be just me 'but', does it seem like the majority of storms these days are moving east to west vs. the west to east? I mean usually storms systems move against eastern sea boarders usually into the east coasts of say the US, Asia, Mexico.. but now (and of course there are storms that hit western seaboards) they are becoming extreme storms moving east and hitting West coasts instead (recently California, now the UK, Ireland). While everyone gets winter storms it just seems like 'more severe' storms are battering the opposing sides of nations.