Weather: The hurricane that never was

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Indy Lifestyle Online
This week sees the 10th anniversary of the Great Gale of 1987 when gusts of wind up to 115mph brought devastation to southern England. It was not the wind speed that made it so unusual, but the fact that it hit London.

Hertford, Hereford and Hampshire are not the only places in the country where hurricanes hardly happen. Mainland Britain simply does not have hurricanes, and Michael Fish was quite correct when he told the notorious lady caller to the BBC that a hurricane was not on its way. It was no more than a severe gale that uprooted our trees, cut off our electricity and gave roof repairers their best business for a generation.

Hurricane force, on the Beaufort scale, is more than 75mph - which means a speed of more than 75mph in the general motion of the wind. Gale force winds (39-63mph) may easily generate gusts of far greater speed, and they are what does the damage.

A true hurricane, however, is not just a question of wind speed; a proper tropical hurricane is a cyclonic wind that swirls, like water gushing ever faster down a plughole, with the apparent ability constantly to replenish and increase its energy. It moves slowly, at some 20-25mph, though the winds about its centre may be of 10 times that speed.

We shall no doubt be seeing this week many of the disaster pictures taken in 1987 - cars crushed by fallen trees, houses with their roofs blown off, woodland with great swaths of trees blown down. In terms of financial damage and human dislocation, it was perhaps the worst storm this country has suffered, yet the meteorological records have evidence of more powerful winds in our recent history.

In 1989, for example, a 140mph gust was recorded at Fraserburgh in the north of Scotland, and Lanarkshire had gusts of more than 120mph in February 1962. Anything above 100mph, however, is very rare in England. The strongest winds that reach these shores come from either the north or the west; their speeds are fuelled by the energy expelled when their water vapour turns into rain (the latent heat of condensation), but once they start moving over land, they usually run out of power.

Just as oceanic water vapour may fuel the growth of a strong wind, the contours of land - as well as its relative dryness - tend to reduce it. The effect of buildings in built-up areas, however, can be to produce eddies and strong winds. The London Weather Centre, situated amidst high office blocks in Holborn, regularly reports significantly more gale-force winds than are measured at Heathrow, where recordings are made well away from tall buildings.

The effect of the 1987 not-quite-a-hurricane was also exaggerated by a number of contributory factors. First, it had been preceded by a rainy spell, leaving the ground wet and trees more easily uprooted; second, the collapse of electricity pylons left some areas in the dark for more than a week, leaving its gloomy effect firmly in the memory.

A proper hurricane, with its great swirling gusts of around 200mph, would have been far worse. Each year the world is hit by around 80 hurricanes which cause, on average, about 20,000 deaths. The perils that Pauline propagated in Mexico were just one small glimpse of the devastation brought by extremes of weather.