Hurricane Matthew was the first Category 5 Atlantic hurricane since Felix in 2007 and the southernmost Category 5 Atlantic hurricane on record. The system originated from a tropical wave that emerged off the west coast of Africa on September 22, and ultimately dissipated as an extratropical cyclone near Atlantic Canada on October 10. Late on September 29, it began a period of explosive intensification that brought it to Category 5 strength early on October 1. It weakened slightly and remained a Category 4 until its landfalls in Haiti and Cuba, afterwards it traversed through the Bahamas and paralleled the coast of Florida until making landfall in South Carolina as a Category 1 hurricane. Matthew later transitioned into a post-tropical cyclone on October 10.
The cyclone was responsible for roughly 600 deaths (with initial reports of up to 1,600), making Matthew the deadliest since Stan in 2005, and caused $15.1 billion (2016 USD) in damages, which made it the costliest since Sandy in 2012. Matthew caused its most destructive entry as it made landfall in Haiti on October 4, causing catastrophic damage and over 500 died as a result. The storm also threatened to be the first major hurricane to strike the United States since Wilma in 2005, however it veered slightly more to the east and remained offshore. The major strike ended up coming a year later. However, torrential rainfall fell in the Carolinas, causing extreme flash flooding. Even as Matthew turned extratropical and moved away from the coast, rivers were still overflowing, and it would take many weeks for the rivers to fall back to average levels. Overall, Matthew caused $10 billion damage in the United States.
Genesis
On September 22–23, a vigorous tropical wave, embedded within the monsoon trough, exited the west coast of Africa over the Atlantic Ocean near Guinea Bissau. The wave coincided with an upper-level trough and an isolated plume of moisture; however, little convection was present. Located unusually close to the equator, roughly 8–10°N, the system was unable to acquire significant spin via the Coriolis force and struggled to develop as it moved rapidly west at . Despite this, the three top forecast models for hurricanes—the GFS, ECMWF, and UKMET—indicated the system would likely become a tropical cyclone over the Caribbean. Two days later, the wave passed south of Cape Verde, and was assessed as having a high probability of tropical cyclogenesis within five days by the National Hurricane Center (NHC). With environmental conditions favoring slow development, thunderstorm activity increased along the wave on September 25, which organized more during the subsequent days while approaching the Lesser Antilles.
By September 27, the wave was producing sustained tropical storm-force winds as reported by the hurricane hunters, although the system lacked the closed circulation required for classification as a tropical cyclone. While the system was passing near Barbados, radar imagery in the Lesser Antilles indicated that the circulation was becoming better organized. Another hurricane hunters flight on September 28 confirmed that a closed circulation developed, recorded surface winds of , and observed hurricane-force gusts at the plane's level. These data in conjunction with microwave satellite imagery indicate the system became a tropical cyclone—earning the designation Tropical Storm Matthew—by 12:00 UTC that day; at this time, the storm was centered 20 mi (30 km) west-northwest of Barbados.
Steered by a strong ridge over the Western Atlantic, Matthew traveled generally west with its center passing between the islands of St. Lucia and St. Vincent before emerging over the Caribbean Sea. Throughout the remainder of September 28, Matthew struggled to develop an inner-core and banding features, preventing intensification. However, deep convection gradually organized around the center. Environmental conditions ahead of the cyclone—including ample moisture fueled by the Intertropical Convergence Zone and high oceanic heat content—favored at least gradual intensification, with the exception of a climatologically unfavorable zone well south of Haiti. Somewhat increased shear on September 29 displaced convection to the east of Matthew's center, leaving behind an exposed circulation. Despite this, aircraft reconnaissance that morning revealed the storm to have deepened somewhat—with a central pressure around . Flight level winds increased to and the aircraft's stepped frequency microwave radiometer (SFMR) observed surface winds of .