A status orange rainfall warning comes into effect across Connacht at 9pm tonight, as Storm Francis arrives.
Met Eireann says intense rainfall associated with Storm Francis is expected at times tonight and tomorrow, with some flash flooding likely.
The rainfall will further elevate river levels, and may result in river flooding also.
The orange rainfall warning will be in effect from 9pm tonight until 5pm tomorrow evening.
Mayo County Council's Flood Preparedness Plan has come into operation ahead of tonight's expected heavy rainfall.
The council says arrangements are being put in place in areas of the county that may be at higher risk of flooding, particularly in Crossmolina town.
Met Eireann is warning of 40-60 mm of rain, with surface flooding in places.
Trees are in full leaf at present, with the potential for a number of trees to fall, blocking roads and damaging power lines.
ESB Networks are preparing for power outages with staff on standby to repair faults in all areas.
The Irish Coast Guard says this is an unusual storm for August, and people are advised to stay away from coastal locations for the duration of the weather warnings.
Al road users should also be aware of hazardous driving conditions, with a danger of fallen trees and debris.
