Storm Debi has made landfall, bringing high winds and heavy rain across the island of Ireland.
Police have urged people to stay at home and avoid unnecessary journeys.
Forecasters have warned of disruption and damager, with severe weather alerts in place.
An amber wind warning has been issued for parts of counties Down and Armagh, with a yellow alert for heavy rain and wind in place for all of Northern Ireland.
In the Republic of Ireland, a red alert – the highest level – was issued for 14 counties with a warning of a danger to life.
Meteorological service Met Éireann said there was a possibility of localised flooding, hazardous driving conditions and fallen trees.
Schools in red warning areas of the Republic of Ireland have been asked to delay opening until 10:00 local time.
This article contains content provided by Twitter. We ask for your permission before anything is loaded, as they may be using cookies and other technologies. You may want to read Twitter cookie policy and privacy policy before accepting. To view this content choose ‘accept and continue’.
End of Twitter content, 1
In Northern Ireland, the yellow rain warning remains in place until 14:00 GMT, with some areas expected to experience up to 40mm of rainfall within a six-hour period.
The Met Office said a spell of very strong winds was expected to develop during the morning across parts of Armagh and Down, with inland gusts of 60-65mph likely in places and coastal gusts of up to 75mph.
An amber warning applies in those areas from 06:00 until 12:00, as Storm Debi moves north.
The Met Office has warned homes and businesses could be affected by Monday’s downpours, just weeks after flooding caused chaos in counties Down, Armagh and Antrim.
‘Do not place yourself in danger’
In a statement, a Police Service of Northern Ireland spokesperson said there was a likelihood of flying debris “which could lead to the possibility of injuries or the potential danger to life”.
They asked people to stay at home where possible and to not make unnecessary journeys.
Newry, Mourne and Down District Council said many of its services would be disrupted due to the amber warning in the area.
Household bin collections will be delayed while recycling centres and public conveniences closed until 12:00 and parks closed until further notice.
In the Republic of Ireland, the red alert for wind means a warning of potential danger to life.
The warning is in place in counties Dublin, Kildare, Laois, Louth, Meath, Wicklow, Offaly and Westmeath until 08:00
It was also in place for counties Clare, Kerry, Limerick, Tipperary, Galway and Roscommon from 02:00 until 05:00 .
Structural damage is expected, and the public have been told to expect significant power outages.
Disruption is also expected at Ireland’s airports and ports. Irish Rail has warned passengers to expect delays as speed restrictions will apply across the Republic of Ireland’s entire rail network for safety reasons due to the storm.
A status orange wind alert is in place for 19 counties until 10:00.
The Republic of Ireland’s National Emergency Co-ordination Group has advised schools and pre-schools in all counties affected to remain closed until 10:00 and for those who can work from home to do so.