Winds of 50mph will batter Northern Ireland, southwest England and west Wales during Thursday night, spreading to Scotland by Friday morning.
Issued this morning at 10:00am, the warning for these counties will be valid from tomorrow night at 10:00pm through to Friday morning at 9:00am.
The Met Office has warned there is a potential "danger to life" from flying debris.
There will also be spells of heavy and persistent rain bringing the risk of localised flooding for Wales, NW and SW England, Northern Ireland and again to western Scotland.
According to the Met Office, gusts of 50 miles per hour are likely with potential for gusts of 60 miles per hour around exposed coasts and hills.
Higher ground in the south and south west could see up to 100mm by the end of the day and the rain is expected to be accompanied by strong winds, gusting up to 60mph.
Storm Callum is now swirling off the southwest coast and will deepen rapidly over the course of the next 12 hours, according to Midland weather expert Cathal Nolan.
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Cllr John Campbell says areas of South Donegal which have been prone to flooding in the past owing to high tides could still be vulnerable.
Arriva Trains Wales is planning to shut the line between 7am and 11am on Friday morning and in the evening.
A National Emergency Coordination group has now been set up in order to deal with the storm.
South Wales is bracing itself for a two-day deluge that's expected to cause flash floods and travel chaos.
"There is also a risk that the high winds associated with Storm Callum, combined with high tides, may lead to some coastal impacts due to large waves".
The forecaster's Atlantic rain charts reveal that Friday's storm will be followed by some heavy rain on Saturday with the next belt following early next week.
NRW has also advised people to take extra care will driving, to avoid walking or driving through any flood water, and to avoid fast flowing rivers and streams.