Meteorology/Tropical cyclones

Where they form

Tropical cyclones form in all hemispheres, although their activity is concentrated in certain areas. The ocean basins in which tropical cyclones most commonly form in are the Northern Indian, Western Pacific, Central Pacific, Eastern Pacific, Northern Atlantic, Southern Pacific, Australian Region, and Southwestern Indian. Elsewhere, storms are rare; for example, only three officially-recognized TCs have formed in the Southern Atlantic. The first occurred in March 2004 and struck Brazil. Dubbed Catarina, its wind speeds reached 100 miles per hour, or 155 kilometers per hour. The second TC formed off the coast of Brazil in March 2010 and was dubbed Anita, while another TC named Iba also formed offshore by Brazil in March 2019.

Northern Hemisphere

The Northern Indian Ocean is responsible for fueling extremely destructive and deadly tropical cyclones, including the deadliest storm worldwide. TCs in this region tend to form between April and December, and their designations vary based on their intensity. Weaker systems are dubbed "depressions" or "deep depressions", while the most intense are known as "very severe cyclonic storms". In 2008, Cyclone Nargis struck Myanmar, causing large-scale devastation.

The Western Pacific sees the most storms; its season runs year-round, and mature tropical cyclones here are called "typhoons". Typhoons, including weaker tropical storms, may number in the dozens every year, and can grow to monstrous sizes and strengths. Typhoon Tip in 1979 holds the record for the strongest tropical cyclone in the world, bearing 1-minute sustained winds of 190 miles per hour. Its pressure sunk to 870 millibars; for comparison, the average air pressure at sea level is over 140 millibars higher. Tip struck Japan after weakening over water.

Hurricanes in the Eastern Pacific are also prolific. Hurricane season has an official boundary in this basin: May 15 to November 30. Nonetheless, storms have been known to occur outside these limits. While hurricanes often strengthen into major cyclones, they usually drift westward and dissipate at sea, causing no major harm to land. Occasionally they recurve northward and strike Mexico or even the United States, though almost always at weakened states. In October 2002, Hurricane Kenna moved ashore in the Mexican state of Nayarit, inflicting substantial damage. In the Central Pacific, hurricanes are much less common, and any storms present in this area usually enter from the Eastern Pacific. Hawaii and Johnston Atoll are the only land in the path of storms.

Storms in the Northern Atlantic, including the Gulf of Mexico and Caribbean Sea, are also referred to as "hurricanes". Each season, defined as between June 1 and November 30, contains an average of around 10 named tropical storms. However, during the 2005 season, 28 storms warranted naming. Most commonly observed in the month of September, hurricanes in the Atlantic often affect land. Among them was Hurricane Katrina, an extremely powerful and catastrophic cyclone that struck the United States in August 2005. Its impact included upwards of $80 billion in damage and approximately 1,836 fatalities.

Southern Hemisphere

The Southern Hemisphere is comprised of three main tropical cyclone basins: the Southwestern Indian (west of west of 90°E), the Australian Region (between 90°E and 160°E), and the Southern Pacific (east of 160°E). The Southern Pacific cyclone season officially runs between December 1 and April 30. On average, 9 tropical cyclones form every season, of which 4.5 will intensify into severe tropical cyclones. The most intense Southern Hemisphere cyclone ever recorded was named Zoe, and formed during December 2002, extending into the following year.

Cyclones in Australia tend to form between November 1 and April 30. The strongest storm ever recorded in the area was Cyclone Gwenda, which occurred during April 1999; other severe storms include cyclones Inigo, George, and Orson.

Finally, in the Southwest Indian, the official cyclone season extends from November 15 to April 30. Storms here commonly impact Madagascar and parts of Africa.