As hurricanes go, Charley was nothing special. It reached the coast of North Carolina on August 17, 1986, moved north along the coast of Maryland, then turned east and headed out over the Atlantic. It caused little damage. Indeed, it brought welcome rain to farmers in the Carolinas, Virginia, and Maryland. There were only three Atlantic hurricanes in that year and none was particularly strong.
Charley, the gentle hurricane, might have been forgotten, only it persisted. Its track carried it right across the North Atlantic and a few days later it reached Britain. By this time it was classified as only a storm. Its warm eyewall had cooled and its winds weakened. Nevertheless, in southwest Wales people were unprepared for its arrival and it caused a great deal of damage. Although officially it was no longer a hurricane, it retained the essential structure of one. It still had the remains of an eyewall of cloud, bringing torrential rain, and behind that the eye, in which the sky was clear and the air still. The eye was followed by the second side of the eyewall, and even fiercer winds. It took two days and the night between to pass. The combination of rain and high seas caused widespread flooding. An inshore lifeboat had to rescue vacationers from one inland trailer park. Dyfed, the northern part of which took the full force of the storm, is the county occupying the peninsula of southwest Wales. It is mainly rural, a sparsely populated place of farms, hills, and small villages. This limited the damage to property. The next hurricane to strike Britain did so in England, with much worse consequences.
Hurricanes can retain their strength as they cross the Atlantic, arriving with enough power to wreak considerable havoc. Floyd, the last hurricane of the 1987 season, formed on October 9, and on the 12th its winds reached more than 75 MPH, the lowest speed to qualify it as a hurricane. It passed through the Florida Keys, but had weakened to less than hurricane force within 12 hours. Then it headed out over the ocean.
European meteorologists saw it coming, but miscalculated its track. This is easily done, because a degree or two can make a great deal of difference. The meteorologists believed that Floyd would pass through the English Channel, well south of the British coast, then head into the North Sea, weakening all the while. Obviously, it would endanger shipping, and the English Channel is one of the busiest sea lanes in the world, but they said people on shore had nothing to fear. It arrived on the night of October 15, traveling a few degrees to the left of its predicted path, and caused havoc throughout the densely populated towns and villages of southern England. Though barely a hurricane in the strict sense, its winds gusted to more than 80 MPH and by dawn on the 16th, 19 million trees had been uprooted. The storm killed 19 people and the damage cost about $2.25 billion (GBP 1.5 billion).
For Scots everywhere, the evening of January 25 is Burns Night, when haggis is paraded to the sound of the bagpipes, a certain amount of whisky is drunk, and the poet is honored by reading aloud from his works. On that day in 1990, Britain, along with much of northwest Europe, suffered the fiercest storm for many years. This time, although it was technically a storm rather than a hurricane, winds reached more than 100 MPH. Its track was predicted accurately, but there was nothing anyone could do to protect property. Roofs were torn from buildings, trees uprooted, power lines brought down, and transport and communications seriously disrupted. Most of Britain was affected and about 47 people died. The storm then moved into continental Europe, killing 19 people in The Netherlands, 10 in Belgium, eight in France, seven in Germany, and four in Denmark. Soon after that, on February 3, 29 people died when winds of hurricane force struck France and Germany, and then on February 26, another wind storm killed at least 51 people in Britain, Netherlands, Germany, France, Belgium, Switzerland, Ireland, and Italy.
Winds strong enough to qualify a storm as a hurricane occur in Europe every few years. In December 1993, for example, a windstorm killed 12 people in Britain, and on January 25 and 26, 1989, hurricane-force winds killed at least 12 people in Spain.
The mid-1980s was a time of little hurricane activity. The Atlantic was quiet. Few tropical storms developed, few of those grew into hurricanes, and those that did were generally weak. Weak storms are just as likely to cross the ocean as strong ones, however, because what matters is not the size or power of the storm, but the distance it travels over land. Over the ocean, hurricanes are sustained by a limitless supply of water. It is evaporating sea water and spray that releases latent heat to feed the vigorous convection needed to build the warm, towering clouds of the eyewall. If, like Charley and Floyd, a hurricane turns north without penetrating the American mainland, there is a chance it will turn east before it begins to weaken significantly.
When steady wind speeds exceed 75 MPH, they are rated as hurricane force on the Beaufort scale, but in Europe they are not really hurricanes, even if that is how they began, far away in the tropical Atlantic. They lack the extreme violence of a tropical cyclone because they are not fed by a very warm sea, and most European “hurricanes” are associated with frontal systems. Tropical cyclones are not frontal.
Over the tropics, the air temperature and pressure is fairly constant throughout vast areas and a very small disturbance is a enough to trigger the development of a tropical cyclone. In mid-latitudes the situation is very different. Air masses with very different characteristics cross constantly, mainly from west to east, and where two air masses meet while moving at different speeds, a front develops. Where a warm and cold front meet at surface level, there is often a region of low pressure called a depression. Air flowing toward a depression is deflected by the Coriolis effect into a spiraling path around it, and the greater the difference in pressure between the center of the depression and the air surrounding it, the stronger the winds will be. As they approach the center, the conservation of their angular momentum causes the winds to increase in speed.
Mid-latitude depressions can be deep, and therefore the winds around them can be strong. Winds often reach gale force and at sea they can reach hurricane force of more than 75 MPH. Winds of this strength are uncommon over land because their passage over uneven ground generates friction, which slows them, but now and then one crosses a coast and may even penetrate deep inland.
To a meteorologist, tropical and mid-latitude depressions are cyclones, regions of low pressure around which air flows cyclonically (counterclockwise in the northern hemisphere), and any cyclone can produce strong winds. Although a tropical cyclone forms in the absence of fronts and most mid-latitude cyclones are frontal, the principal difference is found at the center. A tropical cyclone forms over very warm water and turns into a hurricane when it develops an eye and eyewall at a markedly higher temperature than the surrounding air. A mid-latitude cyclone lacks this warm core. It is the warmth that drives the hurricane, and without it mid-latitude depressions may produce fierce storms, but they can never grow into full-scale hurricanes.
This is the third article of a five-part series on hurricanes. The others can be found at the links below.