Ophelia - the storm expected to bring 80mph winds to Britain and Ireland on Monday - was first tracked nearly 900 miles off the coast of the Azores on October 9.
Here is a timeline of how the storm has developed:
:: October 9 - The US National Hurricane Centre issue an advisory after a tropical depression was found in the Atlantic. At that point, the storm had not been named and was referred to as "Tropical Depression Seventeen", with winds of 35mph being recorded in its position 875 miles to the west of the Azores. The advisory said: "Some strengthening is forecast, and the depression is expected to become a tropical storm later today or tonight."
:: October 9 - The depression does strengthen into a tropical storm and is given the name Ophelia - the 15th named storm of the Atlantic hurricane season.
:: October 10 - The NHC record tropical-storm-force winds more than 100 miles from the centre of the storm and say "gradual strengthening is forecast." The centre expect it to be reclassified as a hurricane by the following day. The storm is still around 800 miles west of the Azores, travelling towards the southeast at 3mph.
:: October 11 - Ophelia becomes a hurricane - the 10th of the season - as it is tracked 760 miles south west of the Azores. The NHC report it is drifting to the northeast and is expected to gather pace on Friday. Winds have increased to 65mph.
:: October 12 - The maximum winds from Ophelia are recorded at 105mph, with two to four inches (50-100mm) of rain forecast to fall in the Azores on Saturday and Sunday. The NHC says: "Some slow weakening is forecast to begin Friday night but Ophelia should remain a hurricane for the next couple of days."
:: October 13 - Ophelia is moving at 20mph in an east-north-easterly direction with maximum sustained winds of 100mph.
:: October 14 - The storm is given a Category 2 status by the NHC, who add: "Little change in strength is expected today, followed by slow weakening on Monday and Tuesday. However Ophelia is still expected to remain a powerful cyclone for the next couple of days as it approaches Ireland." The NHC later upgrade the hurricane to a Category 3.
:: October 15 - The NHC say Ophelia is "now taking aim on Ireland", with maximum recorded gusts of 105mph, travelling at 35mph. The centre adds: "Some additional weakening is expected today and on Monday, but Ophelia is forecast to become a powerful post-tropical cyclone with hurricane-force winds as it approaches Ireland on Monday."
The storm is forecast to produce up to three inches of rain (75mm), a "dangerous storm surge" and dangerous winds. The centre says: "Preparations to protect lives and property should be rushed to completion by this afternoon."
The Met Office in the UK issue a yellow severe weather warning for wind for a western tranche of the country, while an amber warning is issued for Northern Ireland. Met Eireann issue a red warning for the Republic of Ireland saying "violent and destructive gusts are forecast with all areas at risk and in particular the southwest and south in the morning, and eastern counties in the afternoon. Also heavy rain and storm surges along some coasts will result in flooding. There is potential risk to lives."
Irish Taoiseach Leo Varadkar tweeted: "Defence forces being deployed in Red weather alert areas and on standby for further action tomorrow."
A number of Aer Lingus flights due to leave on Monday are cancelled, and it is announced schools, government buildings and courts are due to close in parts of Ireland. Similar measures are put in place in Northern Ireland, with the Executive tweeting: "@Education_NI has announced that all schools should close tomorrow (Monday 16 October) as precautionary measure in light of weather warnings."
:: October 16 - The NHC downgrade Ophelia to a post-tropical cyclone in an advisory sent at 4am UK time, saying the storm is moving to the north at 38 knots (44mph).