During 2021, tropical cyclones formed in seven major bodies of water, commonly known as tropical cyclone basins. Tropical cyclones will be assigned names by various weather agencies if they attain maximum sustained winds of . During the year, 137 systems have formed and 95 were named, including one subtropical depression and excluding one system, which was unofficial. One storm was given two names by the same RSMC. The most intense storm of the year was Typhoon Surigae, with maximum 10-minute sustained wind speeds of and a minimum pressure of . The deadliest tropical cyclone was Typhoon Rai, which caused 410 fatalities in the Philippines and 1 in Vietnam, while the costliest was Hurricane Ida, which caused an estimated $75.25 billion USD in damage after striking Louisiana and the Northeastern United States.

Like last year, 2021 had an above average amount of tropical cyclones globally. The most active basin of the year was the West Pacific, which had another below average season, with only 23 named storms. The North Atlantic had another very active season, producing 21 named storms, while the East Pacific featured average activity, with 19 named storms forming in the basin. The North Indian basin was also average, featuring 5 named storms. The Southern Hemisphere featured relatively average activity, with Cyclones Faraji and Niran both attaining Category 5 intensity. The rest of the Category 5 tropical cyclones occurred in the West Pacific, totalling to six Category 5 tropical cyclones that formed during the year, tying 2003. However, the number of major tropical cyclones across the world was below average, with only 16 forming. The accumulated cyclone energy (ACE) index for 2021 (seven basins combined), as calculated by Colorado State University (CSU) was 621.1 units overall, which was below the 1991-2020 mean of 789.0 units globally.

Tropical cyclones are primarily monitored by a group of ten warning centers, which have been designated as a Regional Specialized Meteorological Centre (RSMC) or a Tropical Cyclone Warning Center (TCWC) by the World Meteorological Organization. These are the United States National Hurricane Center (NHC) and Central Pacific Hurricane Center, the Japan Meteorological Agency (JMA), the Indian Meteorological Department (IMD), Météo-France (MFR), Indonesia's Badan Meteorologi, Klimatologi, dan Geofisika, the Australian Bureau of Meteorology (BOM), Papua New Guinea's National Weather Service, the Fiji Meteorological Service (FMS) as well as New Zealand's MetService. Other notable warning centers include the Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA), the United States Joint Typhoon Warning Center (JTWC), and the Brazilian Navy Hydrographic Center (BNHC).

Global atmospheric and hydrological conditions

The La Niña from the previous year persisted into 2021, though by March and April it had begun to weaken. On May 13, the National Oceanic and Atmospheric Administration (NOAA) assessed that the El Niño–Southern Oscillation (ENSO) transitioned into its neutral phase. However, following cooler than normal temperatures in the tropical eastern Pacific Ocean, NOAA declared that the global weather conditions shifted back to La Niña by October.

Two systems, Tropical Depression 05 and Severe Tropical Storm Danilo persisted into 2021 after developing within the South-West Indian Ocean during December 2020. The COVID-19 pandemic disrupted responses and recovery in areas affected by tropical cyclones.

Summary

North Atlantic Ocean

The 2021 Atlantic hurricane season officially ran from June 1 to November 30. A total of 21 tropical depressions formed, all of which reached at least tropical or subtropical intensity. The season ranks as the third-most active of all time in the Atlantic basin, behind only 2005 and 2020. Consequently, the 2021 Atlantic hurricane season was the third on record to exhaust its naming list. Nine of the systems lasted for two days or less, tied with 2007 for the most since the NHC began monitoring subtropical systems in 1968. Although the season was highly active in terms of the number of named storms, seven of those tropical or subtropical systems intensified into a hurricane and four of those became a major hurricane, which is near-average and just slightly above-average, respectively. Nonetheless, 2021 marked the record sixth consecutive above-average season in the Atlantic. The ongoing warm Atlantic multidecadal oscillation, which began in 1995, contributed to the season's high level of activity, as it led to above-average sea surface temperatures in the Atlantic basin. Other factors included the presence of a La Niña and abnormally heavy West African Monsoon precipitation.

Collectively, the tropical and subtropical systems of the 2021 Atlantic hurricane season caused 194 deaths and about $80.727 billion in damage,

making it the third costliest season on record. Eight named storms struck the United States, which is the third most ever, behind only the previous season and 1916. In conjunction with 2020, 19 systems of at least tropical storm intensity made landfall in the country during the two seasons, surpassing the record of 15 during the 2004 and 2005 seasons combined. As a result, some regions significantly impacted during the 2020 season were once again hit hard in 2021, especially eastern Louisiana and portions of the Northeastern United States. Rhode Island was struck by two tropical systems, Elsa and Henri, an unusual occurrence especially given that the state had recorded no landfalls since Bob in 1991. Four tropical cyclones or their remnantsElsa, Fred, Ida, and Nicholaseach caused at least $1 billion in damage in the United States. The ACE index for the 2021 Atlantic hurricane season, as calculated by Colorado State University using data from the NHC, was approximately 146 units. The totals represent the sum of the squares for every (sub)tropical storm's intensity of over , divided by 10,000. Therefore, the ACE index value does not include tropical depressions. Each season dating back to 2016 recorded ACE index values exceeding 129, which senior research associate Brian McNoldy of the University of Miami described as "unprecedented even for four years, let alone six!" Throughout the season, NOAA Hurricane Hunters logged 462.2 flight hours, conducting 58 eyewall passages and deploying 1,310 dropsondes in the process. NOAA also deployed 66 underwater gliders, which made 78,328 observations on oceanic salinity and temperatures. Additionally, NOAA used five unmanned saildrones to increase documentation on atmospheric and oceanic conditions across the Atlantic basin. One of the five saildrones became the first research vessel to ever enter a major hurricane when it reached Hurricane Sam on September 30. It recorded sustained winds of and waves up to in height while also capturing video footage from inside the storm.

Tropical Storm Ana formed on May 22, making 2021 the seventh consecutive year in which a tropical or subtropical cyclone formed before the season's official start. Ana formed in a location where no tropical storms within the month of May had been documented since before 1950. In mid-June, a rapidly developing non-tropical low offshore of the North Carolina coast became Tropical Storm Bill. The system lasted for only two days before becoming extratropical. Later that month, Tropical Storm Claudette formed just off the coast of Louisiana and Tropical Storm Danny developed offshore South Carolina. Overall, June featured three named storms, tied with 1886, 1909, 1936, and 1968 for the most during that month. Elsa formed on June 30 and became a tropical storm on the following day, making it the earliest fifth-named storm on record, surpassing the previous record by five days, set by Tropical Storm Edouard in 2020. It soon became the first hurricane of the season before impacting the Caribbean and making landfall in Cuba. Later, Elsa brought impacts to the Eastern United States, striking Florida on July 7 and New York and Rhode Island on July 9. Thereafter, activity came to a monthlong halt due to unfavorable conditions across the basin.

On August 11, Fred formed in the eastern Caribbean, bringing impacts to the Greater and Lesser Antilles, and the Southeastern United States. A few days later, Grace formed and strengthened into the second hurricane and first major hurricane of the season, and brought impacts to the Greater Antilles and the Yucatán Peninsula, before making landfall in the Mexican state of Veracruz. A third tropical system, Henri, developed on August 16, near Bermuda. Henri meandered for several days before becoming the third hurricane of the season on August 21 and impacted New England, causing record flooding in some places. Towards the end of the month, Hurricane Ida formed, leaving major damage in western Cuba before rapidly intensifying into a Category 4 hurricane and making landfall in southeastern Louisiana at peak intensity, producing widespread, catastrophic damage. Its remnants then generated a deadly tornado outbreak and widespread, record-breaking flooding across the Northeastern United States. Two other tropical storms, Julian and Kate, also existed briefly during this time but remained at sea. Larry formed on the last day of August and strengthened into a major hurricane early in September. It became the first hurricane to make landfall on Newfoundland since Igor in 2010. As the mid-point of the hurricane season approached, Mindy formed on September 8 and struck the Florida Panhandle shortly thereafter. It was followed by Nicholas, which developed on September 12 and made landfall along the central Texas coast two days later as a hurricane. Three tropical storms—Odette, Peter, and Rose—then formed in quick succession and were steered by prevailing winds away from any interaction with land. The busy pace of storm-formation continued late into September. Sam, a long-lived major hurricane, developed in the central tropical Atlantic and proceeded to rapidly intensify from a tropical depression to a hurricane within 24 hours on September 23 and 24. Sam peaked in strength on September 26 as a high-end Category 4 hurricane. It remained a major hurricane (Category 3 or stronger) for nearly eight consecutive days, the longest continuous stretch at that intensity for an Atlantic hurricane since Ivan, in 2004. Meanwhile, Subtropical Storm Teresa formed north of Bermuda on September 24. Short-lived Victor developed late in the month at an unusually low latitude of 8.1°N, tying Kirk in 2018 and behind only an unnamed 1902 hurricane (7.7°N) for the southernmost location in which an Atlantic system has reached tropical storm intensity.

However, tropical cyclogenesis then paused again for much of the month of October, primarily due to the presence of drier air. For the first time since 2006 and only the second time during the hyperactive era which began in 1995, no named storms developed between October 6 and October 30. Finally, Subtropical Storm Wanda formed in the central North Atlantic on October 30 and transitioned into a fully tropical storm on November 1. This system was the same storm that previously had brought rain and damaging wind gusts to southern New England as a potent nor'easter. Wanda remained a tropical cyclone until transitioning into an extratropical low on November 7, which marked the conclusion of activity during the 2021 Atlantic hurricane season.

Eastern & Central Pacific Oceans