Storms and Hurricanes

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Thunderstorms form when warm, moist air rises rapidly in cumulonimbus clouds, producing lightning, thunder (rapid heating of air), heavy rain and sometimes hail. Tornadoes are rotating funnels of wind from severe storms. Hurricanes (typhoons, cyclones) form over warm oceans (above 26 °C) as low-pressure systems drawing energy from water vapour, with an eye of calm at the centre.

Storm surge, wind and flooding cause the damage. Satellite tracking and warnings save lives.

Lightning gets its energy from charge separation in the cloud, as ice particles collide and move electric charge. A bolt may heat air to about 30,000 degrees C, hotter than the Sun's surface, and the air expands explosively as thunder. Light travels almost instantly while sound takes about 3 seconds per kilometre, so counting seconds between the flash and the bang shows how far away the strike is. Tornadoes may have winds over 300 km/h and are rated on the Enhanced Fujita scale from EF0 to EF5.

A hurricane gets its fuel from warm sea surface evaporating and condensing, releasing latent heat; it weakens quickly over land or cold water. The Saffir-Simpson scale rates them from Category 1 to 5 by wind speed, but storm surge, a dome of seawater pushed ashore, is often the deadliest part, as in Hurricane Katrina in 2005. Tropical cyclones spin counter-clockwise in the north and clockwise in the south. Forecasters use satellites, hurricane hunter aircraft and models to give track warnings days ahead. A common misconception is that the eye is the safest place to be for long; the eye is followed by the opposite eyewall winds. Another is that lightning never strikes twice; it often hits tall objects repeatedly.