Accumulated cyclone energy in the context of "Tropical cyclones"

The 2017 Atlantic hurricane season was a devastating and extremely active Atlantic hurricane season that became the costliest tropical cyclone season on record worldwide, with a damage total of at least $294.92 billion (USD). It was the second consecutive above–average season dating back to 2016. The season featured 17 named storms, 10 hurricanes, and 6 major hurricanes. Most of the season's damage was due to hurricanes Harvey, Irma, and Maria. Another notable hurricane, Nate, was the worst natural disaster in Costa Rican history. These four storm names were retired following the season due to the number of deaths and amount of damage they caused. Collectively, the tropical cyclones were responsible for at least 3,364 deaths. The season also had one of the highest accumulated cyclone energy (ACE) on record, with an index of 225 units. A record three hurricanes generated an ACE of over 40: Irma, Jose, and Maria. This season featured two Category 5 hurricanes, and the only season other than 2007 with two hurricanes making landfall at that intensity. The season's ten hurricanes occurred one after the other, the greatest number of consecutive hurricanes in the satellite era, and tied for the highest number of consecutive hurricanes ever observed in the Atlantic basin.

The season officially began on June 1 and ended on November 30. These dates historically describe the period of year when most tropical cyclones form in the Atlantic basin and are adopted by convention. However, as shown by Tropical Storm Arlene in April, the formation of tropical cyclones was possible at other times of the year. In late August, Hurricane Harvey struck Texas and became the first major hurricane to make landfall in the United States since Wilma in 2005, ending a record 12-year span in which no hurricanes made landfall at the intensity of a major hurricane throughout the United States and was the strongest since Charley in 2004. With damages estimated at $125 billion, the storm sequentially tied Hurricane Katrina for the costliest tropical cyclone on record and broke the record for most rainfall dropped by a tropical cyclone in the United States, with extreme flooding in the Houston area. In early September, Hurricane Irma became the first Category 5 hurricane to impact the northern Leeward Islands on record, later making landfall in the Florida Keys as a Category 4 hurricane. In terms of sustained winds, Irma, at the time, became the strongest hurricane ever recorded in the Atlantic basin outside of the Gulf of Mexico and Caribbean, with maximum sustained winds of 180 mph (285 km/h); it was later surpassed in 2019 by Hurricane Dorian. In mid September, Hurricane Maria became the first Category 5 hurricane in history to strike the island of Dominica. It later made landfall in Puerto Rico as a high-end Category 4 hurricane with catastrophic effect. Most of the deaths from this season occurred from Maria. In early October, Hurricane Nate became the fastest-moving tropical cyclone in the Gulf of Mexico on record and the third hurricane to strike the contiguous United States in 2017. Slightly over a week later, Hurricane Ophelia became the easternmost major hurricane in the Atlantic basin on record, and later impacted most of northern Europe as an extratropical cyclone. The season concluded with Tropical Storm Rina, which became extratropical on November 9.

The 2004 Atlantic hurricane season was a very deadly, destructive, and extremely active Atlantic hurricane season, with over 3,200 deaths and more than $61 billion (2004 USD, $95.77 billion 2022 USD) in damage. More than half of the 16 tropical cyclones brushed or struck the United States. Due to the development of a Modoki El Niño – a rare type of El Niño in which unfavorable conditions are produced over the Eastern Pacific instead of the Atlantic basin due to warmer sea surface temperatures farther west along the equatorial Pacific – activity was above average. The season officially began on June 1 and ended on November 30, though the season's last storm, Otto, dissipated on December 3, extending the season beyond its traditional boundaries. The first storm, Alex, developed offshore of the Southeastern United States on July 31, one of the latest dates on record to see the formation of the first system in an Atlantic hurricane season. It brushed the Carolinas and the Mid-Atlantic, causing one death and $7.5 million (2004 USD) in damage. Several other storms caused only minor impacts, if any. The season was the first to exceed 200 units in accumulated cyclone energy (ACE) since 1995, mostly from Hurricane Ivan, which produced the highest ACE out of any storm this season. Ivan generated the second-highest ACE in the Atlantic, only behind the 1899 San Ciriaco Hurricane.

There are four notable storms: Hurricane Charley, that made landfall in Florida as a Category 4 hurricane on the Saffir–Simpson hurricane wind scale (SSHWS), causing $16 billion in damage in the United States alone. Later in August, Hurricane Frances struck the Bahamas and Florida, causing at least 49 deaths and $10.1 billion in damage. The costliest and most intense storm was Hurricane Ivan. It was a Category 5 hurricane that devastated multiple countries adjacent to the Caribbean, before entering the Gulf of Mexico and causing catastrophic damage on the Gulf Coast of the United States, especially in the states of Alabama and Florida. Throughout the countries it passed through, Ivan caused 129 fatalities and over $26.1 billion in damage. The deadliest storm was Hurricane Jeanne, which caused torrential rainfall in the mountainous areas of Haiti, resulting in mudslides and severe flooding that caused at least 3,000 fatalities. Jeanne also struck Florida, inflicting extensive destruction. Overall, the storm caused at least $7.94 billion in damage and 3,042 deaths, ranking it as one of the deadliest Atlantic hurricanes in history.

The 2013 Atlantic hurricane season was a well below average Atlantic hurricane season in terms of the number of hurricanes and ACE. It was the first since 1994 with no major hurricanes, Category 3 or higher on the Saffir–Simpson scale, and the first in the satellite era where no hurricanes reached Category 2 strength. Altogether, the season produced 15 tropical cyclones, of which all but one became a named storm. The season officially began on June 1, and ended on November 30. These dates historically describe the period in each year when most tropical cyclogenesis occurs in the North Atlantic and are adopted by convention. The first storm of the season, Andrea, developed on June 5, while the last, an unnamed subtropical storm, dissipated on December 7. Throughout the year, only two storms, Humberto and Ingrid, reached hurricane strength; this was the lowest seasonal total since 1982.

The season's overall impact was minimal; although 15 tropical cyclones developed, most were weak or remained at sea. Tropical Storm Andrea killed four people after making landfall in Florida and moving up the East Coast of the United States. In early July, Tropical Storm Chantal moved through the Windward Islands, causing one fatality, but minimal damage overall. Tropical storms Dorian and Erin and Hurricane Humberto brought only squally weather to the Cape Verde Islands. Mexico, where Hurricane Ingrid, Tropical Depression Eight, and tropical storms Barry and Fernand all made landfall, was the hardest hit; Ingrid alone caused at least 32 deaths and $1.5 billion (2013 USD) in damage. In early October, Karen brought showers and gusty winds to the central Gulf Coast of the United States, before impacting the U.S. East Coast as a long-lived nor'easter.

Tropical cyclones are ranked on one of five tropical cyclone intensity scales, according to their maximum sustained winds and which tropical cyclone basins they are located in. Only a few classifications are used officially by the meteorological agencies monitoring the tropical cyclones, but other scales also exist, such as accumulated cyclone energy, the Power Dissipation Index, the Integrated Kinetic Energy Index, and the Hurricane Severity Index.

Tropical cyclones that develop in the Northern Hemisphere are classified by the warning centres on one of three intensity scales. Tropical cyclones or subtropical cyclones that exist within the North Atlantic Ocean or the North-eastern Pacific Ocean are classified as either tropical depressions or tropical storms. Should a system intensify further and become a hurricane, then it will be classified on the Saffir–Simpson hurricane wind scale, and is based on the estimated maximum sustained winds over a 1-minute period. In the Western Pacific, the ESCAP/WMO Typhoon Committee uses four separate classifications for tropical cyclones that exist within the basin, which are based on the estimated maximum sustained winds over a 10-minute period.