|Super Typhoon Songda had peak winds of 240 kph as it grazed the Philippines in May 2011 [NASA]|
The world of tropical storms can be very confusing. There are typhoons and super typhoons, and tropical storms and tropical depressions, but what’s the difference between them all?
Tropical storm systems are all areas of low pressure which bring torrential rain and strong winds. They develop near the equator and get their energy from warm surface waters; if the waters aren’t warm enough, then the storms simply can’t develop.
The weakest type of tropical storm is a tropical depression. If the system is a little stronger, it becomes a tropical storm. The next category up is more powerful again, but the exact name differs depending on where you are in the world.
The umbrella term for all these tropical systems is a tropical cyclone, but as these vast, powerful storms have always played a part in the climate of different regions, so around the world they have developed different names. Around the Americas they are called hurricanes, around Japan and the Philippines they are typhoons and around Australia and the Indian Ocean they are simply called tropical cyclones. They are all the same thing, just with a different name.
To add to the confusion, the Meteorological Agencies of different countries have different requirements for the storm to be classed as a depression, storm or cyclone. The storms have one further sub-category too: if a typhoon becomes really intense, with winds over 211 kph, then it is classed as a super typhoon. The most powerful tropical cyclone is also classed as a severe tropical cyclone, but hurricanes are a little different.
Hurricanes are rated on the Saffir-Simpson Scale, with one being the weakest and five being the most powerful. A major hurricane is a hurricane which is a category three or above.
Although, it may be instinctive to think that the most powerful storm should be the most destructive, often it is the amount of rainfall that these systems bring which can cause the most damage. Even a weaker system can bring devastating flooding and landslides, especially if it is slow-moving and remains in place for several days.
Often a number of these tropical systems will exist at any one time, so to ensure there is no confusion between the storms, they are given names. There are lists of these names which are used in rotation, but sometimes a name is ‘retired’ if a storm causes severe damage, for example the name Katrina will not be used for storms again, after Hurricane Katrina devastated much of New Orleans in 2005.
The storms around the Americas are named in alphabetical order, but there are two lists of names: One for the Atlantic and one for the Pacific. This is why you may hear of two storms which start with the same letter, like Eugene and Emily. Eugene is to the west of Mexico, whereas Emily is forming over the Caribbean.
For the Americas, the storm season ends in November, at which point it starts for Australia and the Southern Indian Ocean. At any point in the year, there is always somewhere preparing for a tropical cyclone, whatever name it is masquerading under.