In Northern Ireland, an amber wind warning has been issued for parts of counties Down and Armagh, with inland gusts of 60-65mph and coastal gusts up to 75mph expected.
A yellow alert for rain and wind is in place for all counties in Northern Ireland from 03:00 GMT to 14:00, with up to 40mm of rainfall predicted in some areas. This comes as many towns and cities are still recovering from recent flooding.
The Met Office has warned of potential damage to buildings and flying debris due to the strong winds, large waves around the coast posing a danger to life, and disruption to travel and infrastructure. In the Republic of Ireland, the National Emergency Co-ordination Group (NECG) met to discuss the storm, describing it as a "severe weather event" with potential for extensive electricity outages and hazardous road conditions.
The red alert in the Republic of Ireland includes counties Clare, Kerry, Limerick, Tipperary, Galway, Roscommon, Dublin, Kildare, Laois, Louth, Meath, Wicklow, Offaly, and Westmeath at varying times. An orange wind alert, the second highest level, has been issued for County Cork and 19 other counties.
Schools and pre-schools in affected counties are advised to remain closed, and people are encouraged to work from home where possible. There are also yellow warnings for the rest of Ireland. Storm Debi is the fourth named storm of the season, which began on September 1.