Katia moves toward Britain as a post-tropical storm on Sept. 12.
Credit: Naval Research Lab.
The leftovers of Hurricane Katia are blowing through Britain today (Sept. 12), an unusual occurrence that is bringing the strongest winds the United Kingdom has seen in nearly 15 years.
Katia has followed an uncommon path for hurricanes, many of which develop over the warm Atlantic waters off the west coast of Africa. Storms that form in this area swirl toward the Caribbean and the United States where they either make landfall or curve back out to sea. A small number — Katia included — have boomeranged all the way back across the Atlantic, though they are typically significantly weakened by that point.
The storms that cross the Atlantic don't have much in common themselves. The atmospheric environment they get caught in is key, said National Hurricane Center spokesman Dennis Feltgen.
"The storms that make it over there are caught up in fast-moving westerly winds," Felgen told OurAmazingPlanet. "So they are flying."
Katia now has transitioned from being a tropical cyclone (the collective term for hurricanes and tropical storms) to being an extratropical storm — one that has both moved poleward and shifted its source of energy.
From 1851 to 2010, only 10 extratropical storms, typically the tail ends of tropical cyclones, have hit within 200 miles (322 kilometers) of Ireland, Feltgen said. Hurricane Debbie was the only tropical hurricane to make landfall in that area, clipping the far northwest of the British Isles in 1961.
By the time storms make it across the Atlantic they are no longer getting their energy from the warm water, and they are similar to the winter storms that blow across the ocean, Feltgen said. Also, the strongest winds are no longer confined to the storm's core as they are in a tightly wound hurricane. Katia is expected to bring winds of up to 80 mph (129 kph).
The last time Britain saw winds this strong was in October 1996, when the end of Hurricane Lili pushed across the Atlantic just one day after being downgraded from a hurricane. With winds of up to 90 mph (145 kph), the storm killed five people in Britain and caused $250 million (150 million pounds) in damage.
Winds from former hurricanes hit Britain and Ireland in 2009, three times in 2006, twice in 2000 and once each in 1996 and 1998, according to the Met Office, Britain's official weather agency.
In 2009, Hurricane Bill crossed the Atlantic and hit the UK as a post-tropical storm. The leftovers of hurricanes Alberto, Gordon and Helene all hit the UK in 2006. Hurricanes Isaac and Leslie hit the British Isles as post-tropical storms in 2000. In 1998, southern Britain was hit by the remnants of Hurricane Karl.
Repeat of Lili?
Both major hurricanes at their peaks, Katia could be similar to Lili in the winds it brings to the UK, according to the Met Office.At its strongest, Katia was a Category 4 storm, the second major hurricane of the 2011 Atlantic hurricane season. Though Katia is now a post-tropical storm, it is capable of producing Lili-like wind gusts that are strong enough to down trees and power lines and cause widespread damage.
Gusty winds from Katia began today (Sept. 12) and will last through the start of the week, with the highest wind speeds of 75 to 80 miles per hour (121 to 129 kph) expected over northern and western regions of the country, according to the Met Office's forecast.
A deep area of low pressure containing Katia is expected to bring the strongest winds to Northern Ireland, the Central Lowlands and southern Scotland and parts of northern England. Large waves could top sea walls in western coastal areas. Parts of western Scotland could flood.
In preparation for the storm, Ireland and Britain shut roads and bridges and canceled sporting events today.
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