Ophelia - the storm expected to bring 130km/h winds to Ireland today - was first tracked nearly 900 miles off the coast of the Azores on 9 October.
Here is a timeline of how the storm developed:
9 October: The US National Hurricane Center issues 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 56km/h 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."
9 October: The depression does strengthen into a tropical storm and is given the name Ophelia - the 15th named storm of the Atlantic hurricane season.
10 October: The NHC records tropical-storm-force winds more than 160km/h from the centre of the storm and says "gradual strengthening is forecast." The centre expects 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.
11 October: Ophelia becomes a hurricane - the 10th of the season - as it is tracked 760 miles southwest of the Azores. The NHC reports it is drifting to the northeast and is expected to gather pace on Friday. Winds have increased to 105km/h.
12 October: The maximum winds from Ophelia are recorded at 170km/h with 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."
13 October: Ophelia is moving at 32km/h in an east-north-easterly direction with maximum sustained winds of over 160km/h.
14 October: The storm is given a Category 2 status by the NHC, which adds: "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 upgrades the hurricane to a Category 3.
15 October: The NHC says Ophelia is "now taking aim on Ireland", with maximum recorded gusts of 170km/h travelling at 56km/h.
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 75mm of rain, a "dangerous storm surge" and dangerous winds.
The centre says: "Preparations to protect lives and property should be rushed to completion by this afternoon."
Met Éireann issues a red warning for 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."
The Met Office in the UK issues a yellow severe weather warning for wind for a western tranche of the country, while an amber warning is issued for Northern Ireland.
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 today are cancelled, and it is announced schools, Government buildings and courts are due to close across Ireland. Similar measures are put in place in Northern Ireland.
16 October: The NHC downgrades Ophelia to a post-tropical cyclone in an advisory sent at 4am Irish time, saying the storm is moving to the north at 70km/h.