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A rapidly intensifying storm will hit northwestern Europe on Wednesday and Thursday, triggering strong winds, heavy rain and flooding. The UK Met Office has named the system Ciarán and it is expected to hit the UK and France particularly hard, while its southern edge will also hit Spain, Portugal and other parts of southern and central Europe.
In Britain, the storm could be one of the strongest in recorded history for 200 years.
Yellow warnings – the second highest level – have been issued for Northern Ireland, west Wales and southern England. There were concerns in Ireland that up to 10cm of rainfall could cause flooding before Ciarán arrived. Southern parts of the UK are bracing for strong winds with gusts between 65 and 80 miles per hour.
“Very strong north-westerly winds associated with Storm Ciarán could disrupt travel and utilities and lead to structural damage,” the Met Office warned.
In France, the situation is even more serious – a rare “sting jet” could blast the northwest coast with winds of 90 to 100 miles per hour. This structure has been responsible for some of Europe’s most devastating storms in the past.
Due to its rapid intensification, the storm is classified as a “bomb cyclone.” It is likely that a second, very severe storm will follow and hit the same region over the weekend.
The storm’s origins can be traced to a strong cold front that was sweeping across the eastern United States and a low pressure zone that formed along that front east of New England.
This low pressure zone will strengthen explosively, driven by an unusually strong jet stream racing across the Atlantic. Like a conveyor belt, it helps airplanes gain speed as they travel east over 700 miles per hour and will hurl the depression towards Great Britain.
Strong winds carried by the jet stream will cross the Atlantic this week, moving from the northeastern United States to western Europe. This area will evolve into Storm #Ciaranwhich will bring strong winds and rain to France and the south of the UK during the week. pic.twitter.com/n6EvXB0JW0
— Zoom Earth (@zoom_earth) October 29, 2023
A storm of record-breaking intensity is possible
The faster a storm intensifies, the less its air pressure drops. Lower barometric pressure means air is lost from the center of the storm, creating a strong vacuum effect that increases the strong winds in the system.
For a storm to be considered a “bomb cyclone,” its minimum central air pressure must fall by 24 millibars, or about 2.4 percent of the surrounding mass of the atmosphere, within 24 hours. This storm could do that in 12 hours, with a total drop of about 37 millibars in 24 hours.
By the time this cyclone reaches its strength, it could have an air pressure of 953 millibars; Typical air pressure at sea level is 1,015 millibars. In most cases, the lower the pressure, the stronger the storm.
According to climate scientist Ed Hawkins of the University of Reading, Ciarán’s prediction is Air pressure would be among the three lowest recorded in southern England in 200 years.
Up to 3 to 4 inches, or about 100 millimeters, of rain is expected in west Wales and west central England. The rest of the UK is expected to receive an inch or two of rain. Local flooding is possible.
Computer models predict about 0.5 to 2 inches of rain in western and northern France.
The northwestern parts of the Iberian Peninsula and western Spain could receive 5 to 7 cm of rainfall. In the high altitudes of Italy, Switzerland, Liechtenstein, Austria, southern Germany, the Czech Republic, Austria, Hungary and Slovenia, five to ten centimeters of rain are possible below freezing point. Individual flooding cannot be ruled out.
There could be 30 to 40 inches of snow in the highlands of the Swiss and German Alps, with a blizzard likely.
Gusts of 40 to 55mph are likely across much of the UK, with gusts of up to 60 to 65mph expected along the south coast. Gusts of 70 miles per hour could occur along the coasts of Belgium and the Netherlands.
Parts of the Iberian Peninsula and France will experience wind gusts of 55 to 65 miles per hour. Northwestern France could see significantly stronger gusts, perhaps approaching 100 miles per hour, due to a so-called “sting jet.”
Dangerous “Sting Jet” possible
There is an increasing risk that winds of 90 to 100 miles per hour could occur along the coast of France and possibly the English Channel. This would occur through the formation of a “sting jet,” or narrow channel of extreme winds, on the southern side of the storm system.
The broader low pressure system rotates counterclockwise. This draws a corridor of jet stream winds south of the low pressure center and sucks a tongue of moisture into the system’s drying slot. Dry air evaporates this moisture quickly, causing cooling, which in turn causes air pockets to sink. This is likely to pull the dynamics of the jet stream to the surface, resulting in a small band of exceptionally fast winds.
These winds would shake the shoreline and reach perhaps a few dozen miles inland.
Sting rays are notoriously difficult to predict but extremely destructive. A surprise stinger jet during the Great Storm of 1987 in northwestern Europe brought a gust of 137 mph to Quimper, Brittany, and 135 mph to the Pointe du Roc in Granville, Normandy. 22 people were killed and nearly $6 billion in damage was caused.