The Met Office is warning that, during the early hours (around 3am) of Thursday, northwesterly winds will develop across the Isles of Scilly and southwestern parts of England and Wales.
Here, gusts are likely to reach 70-80 mph in some coastal areas and in a few coastal spots may exceed 85 mph.
Inland, gusts of 65-75 mph are possible.
A sharp cut-off is expected regarding how far northeast these very high winds extend, but this boundary is still uncertain and dependent on the exact track of Storm Ciarán.
Wind will gradually start to ease from mid-morning but the alert lasts until 1pm.
Very large waves could bring additional impacts to coastal areas of Cornwall, Devon and South Wales.
- Flying debris could result in a danger to life
- Damage to buildings and homes is possible, with roofs blown off and trees and power lines brought down
- Roads, bridges and railway lines may close, with delays and cancellations to bus, train, ferry services and flights
- Power cuts could occur and affect other services, such as mobile phone coverage
- There is potential for large waves and beach material being thrown onto sea fronts, coastal roads and properties