Prediction of Storm Hazards (AQA AS Geography): Revision Note

Measuring Tropical Storms

• One of the most common measures of a tropical storm’s intensity is the five-point Saffir-Simpson scale which is based on wind speeds

• It rates storms from Category 1 (weakest) to Category 5 (strongest)

• Tropical storms are considered major when they reach category 3 and have wind speeds between 111-129 miles (178-208 kilometres) per hour

• A category 5 storm can deliver wind speeds of more than 157 miles (252km) an hour

Saffir-Simpson 5-Point Scale of Wind Strength

Frequency & Regularity of Storm Hazards

• Tropical storms are relatively frequent in many parts of the world, but the frequency can vary significantly from year to year

• On average, there are about 80 tropical storms each year

• The highest number of tropical storms form over the Pacific Ocean (on average over 50 per year)

• In the Atlantic Basin (which includes the Caribbean Sea and the Gulf of Mexico) an average of 12 tropical storms form each season, with around 6 of these becoming hurricanes

• Tropical storms tend to occur during tropical storm season

  • In the Northern Hemisphere, this runs from June to November, with the peak months falling in August, September and October

  • In the Southern Hemisphere, the season runs from November to April, with peak months falling in January, February and March

  • It can be useful that most storms occur at particular times of year in terms of preparation and monitoring

Prediction of Storm Hazards

• Prediction of tropical storms involves gathering data from a wide range of sources such as satellites, weather balloons, radar and ocean buoys

• The data includes atmospheric pressure, wind speed and direction, humidity, sea surface temperatures and ocean currents

• The data is fed into computer models that simulate the behaviour of the atmosphere and ocean to help predict the likely path and intensity of the storm

• Although these models are sophisticated, uncertainties remain and predictions are not always accurate and precise, especially over the longer term

• The path of a tropical storm can be erratic, so landfall is not easy to predict accurately and precisely in advance

• Every year, the NOAA (US National Oceanographic and Atmospheric Administration) releases long-term predictions of tropical storm activity for the coming season

  • This is based on historical data as well as current and projected climate conditions such as ocean temperatures and atmospheric conditions