Typhoon notes

Mother Nature is in one of her evil moods today, having a major tantrum in Taiwan. Category 4 typhoon Krosa is raging there, with sustained winds of 115 mph, gusting to 140 mph. Power outages are widespread, with floods and landslides occurring. At least two people are reported to have died. The storm is heading west across the island, and will presently veer north towards Shanghai, whilst weakening. Preparations for Taiwan's national day, October 10th, have been postponed. Krosa is the 15th named storm of the Western Pacific season - which incidentally runs all year round.

Hurricanes, typhoons and tropical cyclones (all the same thing) are a safety valve in the earth's atmosphere, designed to syphon the sun's energy away from the tropics into higher latitudes. The sun's energy is contained in warm seawater - a hurricane requires waters of 27C / 80F or warmer to form, and this warmth to be contained to a considerable depth. Western Europe and the American and Canadian eastern seaboard sometimes get the remnants of hurricanes. In September 2006, hurricane Gordon spun up the Irish Sea, and it was estimated that it was still a tropical storm at that time.

When I talk of the hurricane of January 2005, I am referring to a normal if very deep depression (central pressure 944 mbar) of the sort we get every day of year here. In the higher latitudes, weathersystems are powered by temperature differences, with a never-ending battle between air from the pole and air from the tropics. Tropical systems are powered by heat. You'll find that a hurricane extends 10 miles up into the atmosphere, with cloud tops having temperatures of -80C / -112F, but the centre of the eye at that altitude running a temperature of +19C / 66F.