The UK Met Office now has a yellow wind warning for Friday and rain warning into Saturday.
Northern Ireland, Wales, western Scotland and the north of England are forecast to see the worst of the weather.
Met Éireann has issued a status Orange warning for Clare and 12 other counties, with gusts of up to 130 kilometres an hour expected overnight tonight.
On Saturday, areas over high ground could see a further 50 to 80mm of rain.
The Met Office's Chief Meteorologist Frank Saunders said: "Strong winds at this time of year can increase the rate of leaf fall which can potentially block drains or culverts and, with the heavy rainfall expected over Friday and Saturday, could well heighten the potential for flooding".
Ireland will bear the brunt of the storm, but gusts of 80mph are expected in parts of Scotland, with up to 10cm of rain falling.
"An orange level warning is issued by Met Éireann for wind speeds with the capacity to produce risky, stormy conditions which may constitute a risk to life and property", a spokesperson said. Stay away from exposed coastal areas for the period of the Status Orange warning and be aware of local conditions in your area, as wind strengths can vary significantly from place to place.
The National Emergency Coordination Group is meeting today to prepare for the arrival of Storm Callum.
Winds of 50mph will batter Northern Ireland, southwest England and west Wales during Thursday night, spreading to Scotland by Friday morning.
All areas are at risk of experiencing stormy conditions, with southern, western and southeastern coastal counties most at risk of seeing winds in excess of 130km/h.
"Additionally there is a concern for storm surge, coastal flooding, and overtopping of waves around coasts, especially Atlantic coasts, due to the coinciding high spring tides".
"There will be storm force or gale force gusts, which can be severe or damaging". There is a chance of gusts of 70 to 80 miles per hour in the Western Isles during Friday afternoon and evening.