https://phys.org/news/2018-11-southern-africa-brace-tropical-cyclones.html

This scale is used to rank tropical cyclones on the basis of a storm's wind speed and pressure: low intensity storms rank as a "1" on the scale, while "5" represents the most intense and damaging tropical cyclones. Category 1 storms are smaller in diameter (50-100km) and have a minimum wind speed of 119km/h, while category 5 storms have wind speeds of 252km/h or more and can span up to 500km in diameter. There's ongoing debate about whether a category "6" should be added to the scale.

As my new research shows, the trend in the South Indian Ocean is shifting. Category 5 tropical cyclones didn't exist in this ocean before 1994. They were recorded for the North Atlantic, North Pacific and South Pacific Oceans throughout most of the 20th century. But since 1994, category 5 storms in the South Indian Ocean have become more frequent.