Prediction of Storm Hazards (AQA A Level Geography)
Revision Note
Written by: Rhiannon Molyneux
Reviewed by: Bridgette Barrett
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
Category | Wind Speeds | Damage |
|---|---|---|
1 | 74-95 mph 119-153 km/h | Some |
2 | 96-100 mph 154-177 km/h | Extensive |
3 | 111-129 mph 178-208 km/h | Devastating |
4 | 130-156 mph 209-251 km/h | Catastrophic |
5 | 157 mph or higher 252 km/h | Catastrophic |
Examiner Tips and Tricks
It is important to note that wind speed is not the only factor that determines the severity of a storm’s impact. Other factors such as the amount of rainfall, storm surges and the nature of the area affected also play a significant role. For this reason, the Saffir-Simpson scale alone is not necessarily an accurate prediction of the likely impact of a storm.
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
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