The 1878 Atlantic hurricane season featured twelve known tropical cyclones, tied with 1886 and 1893 for the second-most active season in the latter half of the 19th century. Of the twelve tropical storms, eight strengthened into hurricanes, while two of those intensified into major hurricanes. However, in the absence of modern satellite and other remote-sensing technologies, only storms that affected populated land areas or encountered ships at sea were recorded, so the actual total could be higher. An undercount bias of zero to six tropical cyclones per year between 1851 and 1885 and zero to four per year between 1886 and 1910 has been estimated.

Of the known 1878 cyclones, both the third and fourth systems were first documented in 1995 by meteorologists José Fernández-Partagás and Henry F. Díaz, who also proposed large changes to the known tracks of the second, seventh, and eighth storms. Further analysis in the early 21st century by the Atlantic hurricane reanalysis project extended the duration of the third system by one day and identified major track changes for the fifth system. However, climate researcher Michael Chenoweth authored a reanalysis study, published in 2014, which concluded that the 1878 season featured a total of seventeen tropical cyclones, with the addition of five undocumented or previously excluded systems from the official hurricane database (HURDAT). Chenoweth also proposed some alterations to the track and intensity of each existing storm. However, these changes have yet to be incorporated into HURDAT.

Seasonal activity began by July 1, when stormy conditions associated with the first system started to impact Florida. All three known cyclones in August intensified into hurricanes and impacted land. Another three systems formed in September and each of them also strengthened into a hurricane. The last of the three, the seventh overall, became the most intense cyclone of the season, peaking as a Category 4 hurricane on the present-day Saffir–Simpson scale. Prior to this, the storm struck Haiti, leading to an unknown number of deaths when a brigantine capsized. Earlier in September, the fifth cyclone inflicted more than $919,000 (1878 USD) throughout its path and killed at least 60 people, with the dead rumored in the hundreds across the Caribbean, particularly in Haiti. In mid-October, the season's eighth storm drowned 27 people offshore New England. Later that month, the eleventh cyclone, the Gale of 1878, rendered substantial storm surge and wind damage throughout the Eastern United States, with 71 deaths and more than $2.46 million in damage. A record-tying five hurricanes existed in the month of October. The twelfth and final known system, which drowned three people in Puerto Rico, was last noted south of Jamaica on December 2. __TOC__

Season summary

The Atlantic hurricane database (HURDAT) recognizes twelve tropical cyclones for 1878 in the Atlantic basin, the highest number in a single season until 1887 and tied with 1886 and 1893 for the second-highest in the latter half of the 19th century. Ten storms attained hurricane status, with winds of 74 mph (118 km/h) or greater, while two of those intensified into major hurricane. The seventh hurricane peaked as a Category 4 hurricane on the present-day Saffir–Simpson scale with maximum sustained winds up to 140 mph (220 km/h) and a minimum atmospheric pressure of , making it a major hurricane. Meteorologists José Fernández-Partagás and Henry F. Diaz first documented the third and fourth cyclones in 1995, while also significantly modifying the tracks of the second, seven, and eighth storms. In the early 21st century, Atlantic hurricane reanalysis project extended the duration of the third system by one day and implemented a major adjustment to the fifth system's track based on a study by Cuban meteorologist Ramón Pérez Suárez. However, a 2014 study by climate researcher Michael Chenoweth recommended the addition of five new cyclones and some alterations to the track and intensity of each existing storm. Chenoweth's study utilizes a more extensive collection of newspapers and ship logs, as well as late 19th century weather maps for the first time, in comparison to previous reanalysis projects. However, Chenoweth's proposals have yet to be incorporated into HURDAT.

Seasonal activity began by July 1, the day when Florida began reporting stormy conditions associated with the season's first cyclone. After this storm was last noted on July 3, more than a month passed before the Lesser Antilles detected the season's second cyclone on August 8. Three systems formed in August, all of which strengthened into hurricanes; each also impacted land. Another three systems formed in September and each of them also strengthened into a hurricane. The first of the three, the fifth cyclone, caused more than $919,000 in losses at least 60 deaths from the Caribbean to the United States and Canada. Some sources suggest that hundreds of fatalities occurred in the Greater and Lesser Antilles, particularly in Haiti. Prior to becoming a Category 4 hurricane, the seventh hurricane struck Haiti as a Category 1 hurricane, compounding the impacts of the fifth storm. With the seventh cyclone existing until at least October 8 and four additional hurricanes forming later that month, this was the most active October on record in terms of number of hurricanes, tied with 1870, 1950, and 2010. The season's eighth storm drowned 27 people offshore New England in mid-October, while the eleventh cyclone, also known as the Gale of 1878, rendered substantial storm surge and wind damage throughout the Eastern United States near the end of the month, with over 71 deaths and more than $2.46 million in damage. After the eleventh storm transitioned into an extratropical cyclone on October 23, the twelfth and final system was first detected east of the Lesser Antilles on November 25. Causing three deaths in Puerto Rico, the cyclone was last noted over the Caribbean Sea south of Jamaica on December 2. Collectively, the storms of the 1878 Atlantic hurricane season caused more than 161 fatalities and over $3.38 million in damage.

The season's activity was reflected with an accumulated cyclone energy (ACE) rating of 181, tied with 1887 for the second highest total of the 19th century and behind only 1893. October alone accounted for a value of 87.8, which remains the all-time highest total in the month of October since HURDAT records began. ACE is a metric used to express the energy used by a tropical cyclone during its lifetime. Therefore, a storm with a longer duration will have higher values of ACE. It is only calculated at six-hour increments in which specific tropical systems are either at or above sustained wind speeds of , which is the threshold for tropical storm intensity. Thus, tropical depressions are not included here.

Systems

Tropical Storm One

Parts of Florida first experienced frequent rain, easterly wind, and decreasing atmospheric pressures on July 1, leading the Atlantic hurricane reanalysis project to initiate the track for this storm approximately west-northwest of Dry Tortugas. The storm made landfall near Marco Island, Florida, on July 2 with sustained winds of 45 mph (75 km/h); Punta Rassa, recorded a minimum pressure of that afternoon. The storm likely briefly weakened to a tropical depression over Florida before emerging into the Atlantic late on July 2 and quickly regained tropical storm status early on July 3. However, the cyclone was last noted several hours later.

Climate scientist Michael Chenoweth proposed that this system formed over the Straits of Florida and initially moved northwestward, passing through the Florida Keys. The storm then turned northeastward and made landfall near Marco Island, but may have dissipated over present-day Palm Beach County instead of emerging into the Atlantic. Key West, Florida, registered a wind of . Rainy weather with frequent easterly gales extended northward through South Carolina. On July 3, easterly gales and rainy weather prevailed along the Atlantic coast as far north as Cape Hatteras. Smithville, North Carolina, registered a maximum wind of from the east.

Hurricane Two

With Guadeloupe reporting squalls and falling atmospheric pressures on August 8, the official track of this cyclone begins just east of the Martinique that day. The system moved generally westward across the Caribbean Sea and then turned northwestward on August 12 south of Jamaica. Shortly after crossing the Yucatán Channel and entering the Gulf of Mexico, the storm likely intensified into a hurricane with maximum sustained winds of 80 mph (130 km/h) early on August 15, based on reports from the bark Padang, which wrecked near Sisal, Yucatán. The storm moved westward across the Gulf of Mexico, and is estimated to have maintained hurricane status until making landfall in Mexico between La Pesca and Tampico in the state of Tamaulipas on August 18. The hurricane rapidly dissipated over Mexico by the next day.

Chenoweth argued that this storm did not exist until August 14, when it was located over the northwestern Caribbean. Additionally, the cyclone moved mostly west-northwest, crossing the northeastern Yucatán Peninsula and later making another landfall near La Pesca, Tamaulipas. The storm caused only minimal in the Lesser Antilles, with Guadeloupe experiencing squalls and barometric pressures falling to . Martinique recorded of precipitation, although this occurred on August 11, making its relation to the cyclone uncertain. In Mexico, Campeche observed heavy rainfall, leading to flooding in the city of the same name. However, Campeche governor Marcelino Castilla and other officials quickly provided disaster relief. Parts of the state of Veracruz reported strong winds, uprooting trees and destroying homes in Tantima, while heavy rains there turned streams into torrents. At Ozuluama, high winds severely damaged or destroyed homes and crops, particularly bananas.

Hurricane Three

A Category 1 hurricane was first observed in western Atlantic, northeast of Bermuda, on August 19 by the bark Arvid. Moving rapidly north-northeastward, the storm grazed Nova Scotia early on the following day. Sydney observed a barometric pressure as low as , forming the basis of the hurricane's estimated maximum sustained wind speed of 90 mph (150 km/h). After also brushing Newfoundland on August 20, the hurricane transitioned into an extratropical cyclone in the Gulf of St. Lawrence several hours later. The storm and its remnants brought heavy rainfall to parts of Atlantic Canada and high winds to eastern Nova Scotia. Chenoweth postulated that this cyclone formed southeast of North Carolina on August 16 and transitioned into an extratropical cyclone just offshore the south coast of Newfoundland late on August 20.

Hurricane Four

Due to ships in the vicinity of the Bahamas reporting severe gales and a barometric pressure as low as , HURDAT initiated the track of this cyclone just south of New Providence on August 25. It moved to the northeast early in its duration, striking Eleuthera shortly thereafter before entering the open Atlantic. By August 26, the cyclone strengthened into a hurricane. Further intensification occurred based on the brig Brittania observing a barometric pressure of , leading the Atlantic hurricane reanalysis project to estimate the storm reached Category 2 status and peaked with winds of 105 mph (165 km/h) on August 28. That day, the hurricane passed within of Bermuda. Only slight weakening occurred as the storm turned more eastward before being last seen on August 30 approximately southeast of Cape Race, Newfoundland.