The 1859 Atlantic hurricane season featured seven hurricanes, the most recorded during an Atlantic hurricane season until 1870. 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 has been estimated. Of the eight known 1859 cyclones, five were first documented in 1995 by Jose Fernandez-Partagás and Henry Diaz, which was largely adopted by the National Oceanic and Atmospheric Administration's Atlantic hurricane reanalysis in their updates to the Atlantic hurricane database (HURDAT), with some adjustments. HURDAT is the official source for hurricane data