The 1856 Atlantic hurricane season featured six tropical cyclones, five of which made landfall. The first system, Hurricane One, was first observed in the Gulf of Mexico on August 9. The final storm, Hurricane Six, was last observed on September 22. These dates fall within the period with the most tropical cyclone activity in the Atlantic. Only two tropical cyclones during the season existed simultaneously. One of the cyclones has only a single known point in its track due to a sparsity of data. Operationally, another tropical cyclone was believed to have existed in the Wilmington, North Carolina area in September, but HURDAT – the official Atlantic hurricane database – excludes this system. Another tropical cyclone that existed over the Northeastern United States in mid-August was later added to HURDAT.
Four tropical cyclones reached hurricane status, including two which became major hurricanes, Category 3 or higher on the modern-day Saffir–Simpson hurricane wind scale. However, in the absence of modern satellite and other remote-sensing technologies, only storms that affected populated land areas or encountered ships at sea are currently known, so the actual total could be higher. An undercount bias of zero to four cyclones per year between 1886 and 1910 has been estimated. The strongest cyclone of the season, the first hurricane, peaked at Category 4 strength with 150 mph (240 km/h) winds. Known as the 1856 Last Island hurricane, it brought devastation to southern Louisiana. More than 200 people were killed after a storm surge submerged Last Island, making it one of the deadliest hurricanes in Louisiana history. Hurricane Two brought heavy rains and squalls to Barbados and Grenada, causing "considerable" damage. Tropical Storms Three and Four had a minor impact on the Northeastern United States and Cuba, respectively. Additionally, Hurricane Five caused four deaths in Inagua, Bahamas and had a minor impact on Cuba and the United States.
The season's activity was reflected with a low accumulated cyclone energy (ACE) rating of 49.
On August 9, a minimal hurricane was observed near the Dry Tortugas. The storm moved northwestward and strengthened, becoming a Category 2 hurricane about 12 hours later. The hurricane reached Category 3 strengthened late on August 9. It continued to deepen and became a Category 4 hurricane on the following day. At 1800 UTC on August 10, the hurricane attained its peak intensity with maximum sustained winds of 150 mph (240 km/h) and a minimum barometric pressure of 934 mbar (27.6 inHg). Simultaneously, the storm made landfall in Last Island, Louisiana. It rapidly weakened inland and fell to tropical storm intensity on August 11. The system then drifted northeastward, until dissipating over Mississippi early on August 12.
Offshore, at least 183 people drowned after steamers and schooners sunk in rough seas produced by the hurricane. A storm surge between 11 and 12 feet (3.4 and 3.7 m) lashed Last Island, Louisiana. The island was completely submerged, with virtually every structure destroyed, including the hotels and casinos, while all crops were ruined. Additionally, Last Island itself split in two. Inland, heavy rainfall caused the Mermentau River, destroying crops and every house in Abbeville. The storm produced up to 13.14 inches (334 mm) of precipitation to New Orleans. In Plaquemines Parish, rice fields were under several feet of water, while many orange trees lost their fruit. The storm resulted in at least 200 fatalities, making it one of the deadliest tropical cyclones in the history of Louisiana.
A hurricane with winds of 80 mph (130 km/h) was initially observed about 750 miles (1,000 km) northwest of the coast of Venezuela on August 13. The cyclone tracked due westward and crossed Grenada, before entering the eastern Caribbean. Heavy rain and squalls were reported in Barbados and Grenada. This system was last noted near La Orchila, Venezuela on August 14.
The third tropical storm of the season developed on August 19 about 170 miles (270 km) southeast of Cape Fear, North Carolina. At 1100 UTC that day, it made landfall near Cape Lookout with winds of 60 mph (95 km/h). The storm traveled north and emerged into the Chesapeake Bay near Norfolk, Virginia. The storm continued travelling northward just offshore of the east coast of the US before finally dissipating off Rhode Island on August 21. Heavy rains and strong winds were reported in Connecticut, Massachusetts, New York, and Washington, D.C. This system was known as the Charter Oak Storm, because it felled the famed Charter Oak in Hartford, Connecticut.
A limited number of sources indicate that a tropical storm was briefly active in the vicinity of Havana, Cuba on August 21.
A hurricane formed north of Hispaniola on August 25. It moved westward, passing over the Inagua Islands before striking the north coast of Cuba as a Category 2 hurricane on August 27. The cyclone weakened to Category 1 strength as it crossed the island, close to Matanzas, but regained first Category 2 and then Category 3 strength as it moved north through the Gulf of Mexico. The cyclone made landfall near Panama City, Florida, on August 31 as a Category 2 hurricane. Thereafter, it then quickly weakened to a tropical storm while moving northward through Georgia and South Carolina. The storm entered the Atlantic from the state of Virginia on next day and dissipated on September 3.
The hurricane destroyed thirty houses on Inagua and four people died there. Several vessels were run ashore on the Cuban coast. In Florida, high tides were reported along the coast. The SS Florida was tossed ashore at St. Joseph Bay and completely destroyed, while streets were inundated with water in Apalachicola. Inland, strong winds and heavy winds brought very damage inland, especially at Marianna, which was considered "a wreak." In Georgia, flooding damaged numerous bridges, damns, and corn and cotton crop fields. Many streets and sidewalks in Columbus were blocked by falling trees. At Norfolk, Virginia, on September 1, the spire of a church was blown down by the storm.
A sixth tropical storm was first observed by the brig Caroline E. Kelly on September 18, which experienced a heavy gale while located about 930 miles (1,500 km) east-southeast of Bermuda. With initial winds of 60 mph (95 km/h), the storm slowly strengthened while moving north-northwestward. At 1200 UTC on September 19, it reached hurricane status and peaked with winds of 80 mph (130 km/h). The storm decelerated and remained at this intensity for over 24 hours. Late on September 21, the system re-curved westward and weakened to a tropical storm. It was last seen by the Pride of the Sea on September 22, while located about 695 miles (1,120 km) south of Cape Race, Newfoundland.