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Sea Science: Hurricanes, typhoons, cyclones have differing intensity scales

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Sea Science: by Jordanna Sheermohamed

Tropical cyclone is, by definition, a universal label for a system originating over tropical waters of clouds and thunderstorms that exhibit a closed circulation in the lower levels of the atmosphere. Specific names observed in different parts of the world include hurricane, typhoon, cyclonic storm or simply cyclone – all dependent on the ocean basin of origin.

The Atlantic hurricane season, beginning June 1 and ending Nov. 30, sees an uptick in cyclonic activity once the ocean basin has had enough time to absorb the sun’s energy and wind shear values in the main development region reduces to conditions conducive for genesis, or strengthening. 

The statistical peak of the Atlantic hurricane season tends to occur during the second week of September, but this doesn’t exclude intense storms from occurring before or after; think of the Category 5 Hurricane Andrew occurring in August and Hurricane Michael in October.

Just like the names differ, intensity categories can also differ based on the geographical location. The Atlantic basin’s Saffir-Simpson scale classifies the intensity of a tropical cyclone by the sustained winds over a one minute time frame. The scale, developed by meteorologist Robert Simpson and structural engineer Herbert Saffir, highlights the inverse relationship of decreasing pressure and increasing winds, which can additionally indicate the potential for damage.

Like the Saffir-Simpson scale, other cyclone intensity scales are also dependent on winds. The Pacific Ocean basin in the Northern Hemisphere is divvied up into three distinct regions – Eastern, Central and Western – with multiple agencies tasked with each region. The Joint Typhoon Warning Center (JTWC), tasked with monitoring cyclone activity to protect U.S. Department of Defense installations and assets in the Northwest Pacific, the South Pacific Ocean and the Indian Ocean. Much like the related National Hurricane Center, the JTWC also classifies their typhoon classifications over one-minute averaged sustained wind speeds.

Other meteorological cyclone monitoring entities around the world have established their own category names, sustained wind time frames, and wind speed ranges to determine intensity. The Japanese Meteorological Agency (JMA), which monitors activity in the Northwest Pacific basin, utilizes a classification that relies on sustained winds over a 10-minute average for three different typhoon categories: strong typhoon, violent typhoon and super typhoon. 

Compare this with the classification established by the Indian Meteorological Department, which classifies cyclones into five categories ranging from cyclonic storm to super cyclonic storm. Météo France actively monitors tropical cyclone activity to protect French territories and further utilizes a three-tier system: tropical cyclone, intense tropical cyclone and very intense tropical cyclone. 

Additional agencies from Australia, New Zealand, Fiji, China, Papua New Guinea and Indonesia all monitor regions of global ocean basins  utilizing categories and scales somewhat like the U.S.-based NHC.

Tropical cyclones are considered one of the most brutal forces of nature, regardless of the category achieved. And regardless of said category, one thing remains key: Remain aware and prepared.

Jordanna Sheermohamed is president and lead meteorologist of Weather Forecast Solutions, a weather-forecasting firm (WeatherForecastSolutions.com).  Comments are welcome below.

About Jordanna Sheermohamed

Jordanna Sheermohamed is president and lead meteorologist of Weather Forecast Solutions, a private weather-forecasting company (www.WeatherForecastSolutions.com). Comments are welcome at editor@the-triton.com.

View all posts by Jordanna Sheermohamed →

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