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In the North Atlantic Ocean, the classification tropical storm is used to refer to a tropical cyclone with 1-minute maximum sustained wind speeds from 39 mph (63 km/h) to 72 mph (117 km/h). Tropical cyclones that attain such winds and move over land while maintaining those winds are capable of causing minor to moderate damage to human lives and infrastructure. Since HURDAT began in 1851, there have been 754 tropical storms recorded, as well as 72 others not recognized by HURDAT, but recognized by the International Best Track Archive for Climate Stewardship (IBTrACS) as possible tropical storms, in the North Atlantic basin, which is denoted as the part of the Atlantic Ocean north of the equator. This list does not include tropical storms that later intensified into hurricanes.

The development of tropical storms in the North Atlantic basin is influenced by many factors. During the Northern Hemisphere winter and spring months of December to April, sea surface temperatures in the tropics are usually too low to support tropical cyclogenesis, and there are multiple high-pressure systems, such as the Azores High, that also inhibit tropical cyclogenesis. These effects are reduced or even disappear during hurricane season from May to November, when sea surface temperatures are also high enough to support tropical cyclogenesis; the bulk of recorded tropical storms developed during June to November. Global weather patterns may also influence hurricane development in the North Atlantic. El Niño events result in reduced numbers of powerful hurricanes through stronger wind shear and lower sea surface temperatures within the basin, while La Niña events increase the number of such hurricanes through the opposite.

Background

On the Saffir–Simpson scale, a tropical cyclone reaches tropical storm status when it attains maximum sustained winds of between 34 knots (39 mph; 63 km/h; 17 m/s) and 63 knots (72 mph; 117 km/h; 32 m/s). The National Hurricane Center (NHC) defines sustained winds as the average wind speed measured over the period of one minute at the height of 10 metres (33 ft) above the ground. Should a tropical storm make landfall, its strongest winds are not especially damaging, and are unlikely to cause damage to any sturdy structure, but can often make trees and their branches fall. A larger danger is a tropical storm's rainfall, which can cause major flooding, as in the case of Tropical Storm Allison, and a slow-moving system can cause severe loss of life.

The North Atlantic tropical cyclone basin is defined as the region of the Atlantic Ocean north of the equator, while other boundaries are mainly established by land areas. The Regional Specialized Meteorological Center (RSMC) for the North Atlantic basin is the NHC, which manages the warnings of tropical cyclones there. On average from 1966 to 2009, eleven tropical cyclones form in one year, though the number can range from only four in 1983 to thirty in 2020. All tropical cyclones recorded by past and present RSMCs of the North Atlantic basin since 1851 are listed in the North Atlantic hurricane database (HURDAT), which is compiled and maintained by the National Hurricane Center.

Climatology

Hurricane season in the Atlantic Ocean begins on June 1 and ends on November 30. Storms that do not form in this time period are known as off-season storms. Since 1851, a total of 754 tropical storms have developed in the North Atlantic Ocean. 35 have occurred in the off-season, 78 in June, 64 in July, 149 in August, 222 in September, 156 in October, and 50 in November.

The formation and development of tropical cyclones, termed tropical cyclogenesis, requires high sea surface temperatures of at least 26.5 °C (79.7 °F) and low vertical wind shear. When these conditions are met, a pre-existing tropical disturbance – usually a tropical wave – can develop into a tropical cyclone, provided the disturbance is far enough from the Equator to experience a sufficiently strong Coriolis force which is responsible for the counterclockwise rotation of hurricanes in the Northern Hemisphere. Although most storms are found within tropical latitudes, occasionally storms will form further north and east from disturbances other than tropical waves such as cold fronts and upper-level lows. These are known as baroclinically induced tropical cyclones. There is a strong correlation between Atlantic hurricane activity in the tropics and the presence of an El Niño or La Niña in the Pacific Ocean. El Niño events increase the wind shear over the Atlantic, producing a less-favorable environment for formation and decreasing tropical activity in the Atlantic basin. Conversely, La Niña causes an increase in activity due to a decrease in wind shear.

Tropical storms can take a variety of different tracks across the Atlantic Ocean. As they are weaker, they do not require as high a sea surface temperature, and they are more likely to form in unusual areas, such as Tropical Storm Grace, the northernmost-forming tropical cyclone in the Atlantic; Tropical Storm Christine, the easternmost-forming tropical cyclone in the Atlantic; or Tropical Storm Delta, which hit Morocco as an extratropical cyclone, the first storm ever to do so.

Systems

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1950–2000

Regular naming of Atlantic storms began in 1950.

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