Unobstructed across the vast expanse of the North Atlantic Ocean, the Irish maritime area encompasses some of the world’s most energy-intensive waves. However, high winds and associated large waves present a substantial engineering challenge to ensure the survivability of offshore renewable energy devices during extreme weather events. Finding adequate weather windows for installation, operation, and maintenance activities is another obstacle when deploying these devices. This paper presents the results of a large-scale analysis of wave and wind data around the coasts of Ireland and Wales. Extreme Value Analysis calculates the expected wave heights and wind speeds for extreme events (1-year, 10-year, 50-year and 100-year return periods). Weather windows are also calculated based on a matrix of wave heights, wind speeds and minimum durations required. A custom-developed GIS (Geographic Information System) tool visualises the results.