The United Kingdom does not experience true hurricanes, a form of tropical cyclone. By the time powerful storms originating in the tropical Atlantic reach the UK, they have undergone a fundamental meteorological transformation. The systems that ultimately impact the British Isles are known as post-tropical or extratropical cyclones, the powerful remnants of former hurricanes. While these storms no longer possess a hurricane’s structure, they frequently retain enough energy to bring damaging winds and widespread heavy rainfall.
Defining Tropical and Extratropical Storms
A hurricane, or tropical cyclone, is characterized by a unique structure fueled entirely by the heat and moisture drawn from very warm ocean waters. These storms feature a distinctive warm core at their center, created as air rising near the eye releases latent heat. Crucially, a tropical cyclone lacks the weather fronts—boundaries between different air masses—that define storms in the mid-latitudes.
Extratropical cyclones are the low-pressure systems typically found over the North Atlantic and the UK. Their power source is not warm sea surface temperatures but horizontal temperature differences (baroclinic instability) between cold polar air and warm subtropical air. This gives them a cold core structure and means they are always associated with cold, warm, or occluded fronts. The storms affecting the UK are either standard extratropical systems or former hurricanes that have completed this transformation.
Why Hurricanes Cannot Survive the Atlantic Crossing
The primary reason hurricanes cannot maintain their identity across the Atlantic is the loss of their necessary fuel source: warm sea water. As a tropical cyclone tracks northward, it moves over increasingly cooler North Atlantic waters, particularly north of about 30 degrees North latitude. Sea surface temperatures below approximately 26 degrees Celsius are insufficient to sustain the hurricane’s warm-core engine.
The environment also becomes increasingly hostile to the storm’s vertical structure. The tropical cyclone encounters stronger environmental winds that vary with height, a condition known as wind shear. This increasing wind shear strips away the storm’s symmetrical structure, which is necessary to maintain its tropical strength. This interaction, often with the mid-latitude jet stream, causes the storm to engage with the surrounding atmosphere’s temperature gradients, initiating the process of extratropical transition.
The Actual Impact of Post-Tropical Systems in the UK
The extratropical transition process causes the storm to lose its tight, hurricane-like eye and expand its wind field significantly. While peak wind speeds may decrease from their tropical maximum, the resulting extratropical storm can re-intensify dramatically by tapping into the baroclinic energy of the mid-latitudes. This transformation means the storm’s strongest winds and heaviest rain are spread over a much wider geographical area.
The most severe hazards to the UK from these post-tropical systems are widespread gale-force winds and extreme rainfall.
Notable Examples
The remnants of Hurricane Katia in 2011 brought wind gusts of up to 72 miles per hour to parts of northern England, causing significant transport disruption and a fatality from a fallen tree. Hurricane Charlie in 1986 is notable for bringing record-breaking rainfall that caused extensive flooding in the British Isles.
A more recent example is Ex-Hurricane Ophelia in 2017, which brought gusts exceeding 80 miles per hour to parts of the UK and Ireland. This storm demonstrated the extensive reach of these systems; its powerful winds also pulled dust from the Sahara Desert and smoke particles from Iberian wildfires over the UK. These post-tropical systems typically arrive during the late summer and autumn (September and October), when the North Atlantic is still relatively warm and tropical activity peaks.