An Overview on Hurricane Categories

A tropical cyclone can come your way as you travel throughout the world. Residents in vulnerable areas are familiar with their region’s storm warnings, but you might not recognize these foreign terms and so not know how dangerous the oncoming storm was. Here is a guide to the major hurricane categories worldwide and how each compares to the one you are most familiar with.

♦ The international standard

The World Meteorological Organization has designated six regional centers and six Tropical Cyclone Warning Centers to provide advisories and bulletins and gather up-to-date weather information. Forecasters in these centers may follow the international category system – tropical depression, tropical storm, severe tropical storm, typhoon/hurricane – but most use their own regional system when it’s time to inform the public about an approaching cyclone. These categories are generally based on wind speed.

Let’s see what different categories Hurricane Irene, which hit New York City in 2011, would have been in, had the same storm threatened other popular international travel destinations.

♦ Hurricane Irene

Hurricane Irene was a Cape Verde type of hurricane that was in several categories of the Saffir-Simpson Hurricane Wind Scale at different stages of its journey over northern Caribbean islands and the Bahamas and then up the eastern seaboard of North America in August 2011.

According to the post-season report on Irene by the National Hurricane Center, which can be downloaded here in PDF format, Tropical Storm Irene became a Category 1 hurricane as it moved over Puerto Rico on August 22. The NHC says that Category 1 winds range from 74 to 95 mph (64 to 82 knots, 33 to 42 m/s) and will produce some damage, but most of Irene’s damage in the islands, as well as 8 deaths, came from rain and storm surge flooding.

By August 24, when it reached the Bahamas, Irene was a major Category 3 hurricane with a peak recorded wind velocity of almost 121 mph (105 knots, 54 m/s). Category 3 winds can cause devastating damage and carry a high risk for injury and death from flying debris. Surprisingly, the NHC reports there no deaths from Irene in the Bahamas, although over the course of its existence this storm killed 49 people, most of them Americans. Irene had dropped back down to Category 1 intensity with 86-mph winds (75 knots, 39 m/s) by the time it made landfall over North Carolina’s Outer Banks on August 27. By the next day, Irene had weakened to tropical storm strength, with maximum winds of 70 mph (60 knots, 31 m/s) at landfall in New Jersey and 63 mph (55 knots, 28 m/s) at its final landfall, over Coney Island and Manhattan, about an hour later.

♦ Hurricanes, typhoons and tropical cyclones

France also uses the Saffir-Simpson scale for hurricanes near its weather outpost on Reunion Island in the southwestern Indian Ocean. However, in the regions around Japan, China, the Philippines and Australia, such storms are known as typhoons or some sort of a cyclone, and there are category differences from the Saffir-Simpson scale that can be a little confusing.

According to NOAA’s Hurricane Research Division, once a system develops winds of 39 mph (34 knots, 17 m/s), it’s a tropical storm everywhere but in Australia’s warning region, where it is called a Category 1 cyclone. When the winds hit 74 mph (64 knots, 33 m/s), it becomes a hurricane in the northern Atlantic and the US warning regions of the Pacific. Elsewhere in the Pacific or in the Indian Ocean, the same storm will be called a “typhoon,” “severe tropical cyclone,” “Category 3 (or above) cyclone,” “very severe cyclonic storm,” or a “tropical cyclone,” depending on your location. Japan is a special case; the Japanese classification of “taifu” or “taihu” covers everything from tropical storms through typhoons.

It sounds confusing but will make sense if you focus only on the terms used by the particular regional warning center whose area you will be visiting during the cyclone season, which runs from roughly June 1st to November 30th in the Northern Hemisphere and from November to April in Australia. The Arabian Sea, Bay of Bengal and southwestern Indian Ocean tropical cyclone seasons vary.

Detailed information about all these areas and links to the relevant tropical cyclone warning center websites (in English) are given at the World Meteorological Organization site. Also, Kitamoto Asanobu offers this handy chart that compares hurricane, typhoon and tropical cyclone categories.

Using the Kitamoto online chart, we can see if a storm like Irene was approaching while you were overseas, warnings would range from a typhoon to a severe tropical storm if you were in, say, Hong Kong. For the same system in the northern Indian Ocean, officials in New Delhi would speaking of a severe to very severe cyclonic storm, while it would be notices of a severe to intense tropical cyclone affecting your vacation in Sidney or Melbourne.

Whether you call them hurricanes, typhoons, tropical cyclones or cyclonic storms, forewarned is forearmed. Now that you have an overview of hurricane categories to go by, you will know what to expect when heavy weather looms while you are traveling.