The 2018 Atlantic hurricane season was the third in a consecutive series of above–average and damaging Atlantic hurricane seasons dating back to 2016, featuring 15 named storms, 8 hurricanes, and 2 major hurricanes, which caused a total of over $50 billion (2018 USD) in damages and at least 172 deaths. More than 98% of the total damage was caused by two hurricanes (Florence and Michael). The season officially began on June 1, 2018, and ended on November 30, 2018. These dates historically describe the period in each year when most tropical cyclones form in the Atlantic basin and are adopted by convention. However, subtropical or tropical cyclogenesis is possible at any time of the year, as demonstrated by the formation of Tropical Storm Alberto on May 25, making this the fourth consecutive year in which a storm developed before the official start of the season. The season concluded with Oscar transitioning into an extratropical cyclone on October 31, almost a month before the official end.
Although several tropical cyclones impacted land, only a few left extensive damage. In mid-September, Hurricane Florence produced disastrous flooding in North Carolina and South Carolina, with damage totaling about $24 billion. The storm also caused 54 deaths. About a month later, Hurricane Michael, the first tropical cyclone to strike the United States as a Category 5 hurricane since Hurricane Andrew in 1992, left extensive damage in Florida, Georgia, and Alabama. Michael caused approximately $25 billion in damage and at least 64 deaths. Since Michael reached Category 5 status, 2018 became the third consecutive season to feature at least one Category 5 hurricane. Hurricane Leslie resulted in the first tropical storm warning being issued for the Madeira region of Portugal. Leslie and its remnants left hundreds of thousands of power outages and downed at least 1,000 trees in the Portuguese mainland, while heavy rains generated by the remains of the cyclone caused 15 deaths in France. The storm left approximately $500 million in damage and 16 fatalities.
Most forecasting groups called for a below-average season due to cooler than normal sea surface temperatures in the tropical Atlantic and the anticipated development of an El Niño. However, the anticipated El Niño failed to develop in time to suppress activity, and despite the aforementioned cooler sea temperatures, activity exceeded most predictions.
Seasonal forecasts
Ahead of and during the season, several national meteorological services and scientific agencies forecast how many named storms, hurricanes, and major hurricanes will form during a season or how many tropical cyclones will affect a particular country. These agencies include the Tropical Storm Risk (TSR) Consortium of University College London, the National Oceanic and Atmospheric Administration (NOAA) and Colorado State University (CSU). The forecasts include weekly and monthly changes in significant factors that help determine the number of tropical storms, hurricanes, and major hurricanes within a particular year. Some of these forecasts also take into consideration what happened in previous seasons and an ongoing La Niña event that had recently formed in November 2017. On average, an Atlantic hurricane season between 1981 and 2010 contained twelve tropical storms, six hurricanes, and three major hurricanes, with an Accumulated Cyclone Energy (ACE) index of between 66 and 103 units. ACE is, broadly speaking, a measure of the power of a hurricane multiplied by the length of time it existed; therefore, long-lived storms and particularly strong systems result in high levels of ACE. The measure is calculated at full advisories for cyclones at tropical storm strength—storms with winds in excess of 39 mph (63 km/h).
Pre-season outlooks
The first forecast for the year was released by TSR on December 7, 2017, which predicted a slightly above-average season for 2018, with a total of 15 named storms, 7 hurricanes, and 3 major hurricanes. On April 5, 2018, CSU released its forecast, predicting a slightly above-average season with 14 named storms, 7 hurricanes, and 3 major hurricanes. TSR released its second forecast on the same day, predicting a slightly-below average hurricane season, with 12 named storms, 6 hurricanes, and 2 major hurricanes, the reduction in both the number and size of storms compared to its first forecast being due to recent anomalous cooling in the far northern and tropical Atlantic. Several days later, on April 16, North Carolina State University released its predictions, forecasting an above-average season, with 14–18 named storms, 7–11 hurricanes, and 3–5 major hurricanes. On April 19, The Weather Company (TWC) released its first forecasts, predicting 2018 to be a near-average season, with a total of 13 named storms, 7 hurricanes, and 2 major hurricanes.
TWC revised their forecast slightly on May 17, instead projecting 12 named storms, 5 hurricanes, and 2 major hurricanes in their May 17 outlook. On May 24, NOAA released their first forecasts, calling for a near to above average season in 2018. On May 25, the UK Met Office released their prediction, predicting 11 tropical storms, 6 hurricanes, and an Accumulated Cyclone Energy (ACE) value of approximately 105 units. In contrast, on May 30, TSR released their updated prediction, significantly reducing their numbers to 9 named storms, 4 hurricanes and 1 major hurricane, citing a sea surface temperature setup analogous of those observed during the cool phase of the Atlantic multidecadal oscillation. On May 31, one day before the season officially began, CSU updated their forecast to include Tropical Storm Alberto, also decreasing their numbers due to anomalous cooling in the tropical and far northern Atlantic.
Mid-season outlooks
On July 2, CSU updated their forecast once more, lowering their numbers again to 11 named storms, 4 hurricanes, and 1 major hurricane, citing the continued cooling in the Atlantic and an increasing chance of El Niño forming later in the year. TSR released their fourth forecast on July 5, retaining the same numbers as their previous forecast. On August 2, CSU updated their forecast again, increasing their numbers to 12 named storms, 5 hurricanes, and 1 major hurricane, citing the increasing chance of a weak El Niño forming later in the year. Four days later, TSR issued their final forecast for the season, slightly increasing their numbers to 11 named storms, 5 hurricanes and only one major hurricane, with the reason of having two unexpected hurricanes forming by the beginning of July. On August 9, 2018, NOAA revised its predictions, forecasting a below-average season with 9–13 named storms, 4–7 hurricanes, and 0–2 major hurricanes for all of the 2018 season.
Seasonal summary
The 2018 Atlantic hurricane season officially began on June 1. The season produced sixteen tropical depressions, all but one of which further intensified into tropical storms. Eight of those strengthened into hurricanes, while two of the six hurricanes further strengthened into major hurricanes. Seven storms received the designation of subtropical cyclone at some point in their duration. Above normal activity occurred due to anomalously warm sea surface temperatures, a stronger west-African monsoon, and the inability for the El Nino to develop during the season. The Atlantic tropical cyclones of 2018 collectively caused 172 fatalities and just over $50.2 billion in damage. The Atlantic hurricane season officially ended on November 30, 2018.
Tropical cyclogenesis began with the formation of Tropical Storm Alberto on May 25, marking the fourth consecutive year that activity began early. However, no storms developed in the month of June. July saw the formation of Beryl and Chris, both of which intensified into hurricanes. August also featured two named storms, Debby and Ernesto, though neither strengthened further than tropical storm status. On August 31, the depression that would later become Hurricane Florence developed. September featured the most activity, with Florence, Gordon, Helene, Isaac, Joyce, Tropical Depression Eleven, Kirk, and Leslie also forming or existing in the month. Florence, Helene, Isaac, and Joyce existed simultaneously for a few days in September, becoming the first time since 2008 that four named storms were active at the same time. The season also became the second consecutive year with three hurricanes simultaneously active.
Activity continued in October, with Michael forming on October 7 and strengthening into a major hurricane over the Gulf of Mexico, before making landfall in the Florida Panhandle at peak intensity. Michael, which peaked as a Category 5 hurricane with maximum sustained winds of 160 mph (260 km/h) and a minimum barometric pressure of 919 mbar (27.1 inHg), was the most intense tropical cyclone of the season and one of only four storms to make landfall in the United States mainland as a Category 5, the others being the 1935 Labor Day hurricane, Hurricane Camille in 1969, and Hurricane Andrew in 1992. After 15 consecutive days as a tropical cyclone, Leslie transitioned into a powerful extratropical cyclone on October 13 while situated approximately 120 mi (195 km) west of the Iberian Peninsula, before making landfall soon afterward. A two-week period of inactivity ensued as the season began to wind down. Oscar, forming as a subtropical storm on October 26, became fully tropical and intensified into a hurricane the next day, making it the eighth hurricane of the season. Oscar's extratropical transition on October 31 effectively brought the season to an end, as no systems formed in November. The seasonal activity was reflected with an Accumulated Cyclone Energy index value of 132.6 units.
Systems
Tropical Storm Alberto
A broad area of low pressure formed over the northwestern Caribbean Sea on May 20 due to the diffluence of a trough. Dry air and wind shear initially prevented development as the low moved over the Yucatán Peninsula. However, after the low re-emerged into the Caribbean on May 25, a well-defined circulation developed and the system became a subtropical depression about 80 mi (130 km) east-southeast of Chetumal, Quintana Roo, around 12:00 UTC. After remaining nearly stationary for the next day, the subtropical depression moved northward and continued strengthening, becoming Subtropical Storm Alberto as it crossed into the Gulf of Mexico late on May 26. After convection migrated closer to the circulation and the Alberto's wind field decreased in size, it transitioned into a tropical storm around 00:00 UTC on May 28. Around that time, Alberto peaked with winds of 65 mph (100 km/h) and a minimum pressure of 990 mbar (29 inHg). Around 21:00 UTC, Alberto made landfall near Laguna Beach, Florida, with winds of 45 mph (75 km/h). The cyclone weakened to a tropical depression shortly after landfall. Possibly due to the brown ocean effect, Alberto persisted as a tropical cyclone over land until transitioning into a remnant low over northern Michigan on May 31.
Alberto and its precursor caused flooding in the Yucatán Peninsula, particularly in Mérida. Flooding also occurred in Cuba, where the cyclone dropped 14.41 in (366 mm) of rainfall in Heriberto Duquezne, Villa Clara. The storm damaged 5,218 homes and 23,680 acres (9,580 ha) of crops throughout the country. Alberto caused 10 deaths in Cuba, all due to drowning. In Florida, sustained winds reached 51 mph (82 km/h) and gusts topped out at 59 mph (95 km/h), both recorded at the St. George Island Bridge. The winds knocked down dozens of trees, some of which fell onto roads, power lines, and a few homes. Storm surge entered five buildings and a restaurant in the Florida Panhandle. Farther inland, Alberto caused flooding in several states. Particularly hard hit was western North Carolina, where flooding and mudslides led to the closure of more than 40 roads, including parts of the Blue Ridge Parkway. Approximately 2,000 people fled their homes in McDowell County due to the threat of failure of the dam at Lake Tahoma. Alberto caused eight deaths and about $125 million in damage in the United States.
Hurricane Beryl
On July 1, a tropical wave and accompanying low-pressure area exited the west coast of Africa. While moving west-southwestward over the next few days, the system organized into a tropical depression at 12:00 UTC on July 4 about 1,495 mi (2,405 km) west-southwest of the Cape Verde Islands. About 12 hours later, the depression intensified into Tropical Storm Beryl. Despite relatively cool sea surface temperatures, Beryl continued to strengthen, becoming a Category 1 hurricane by 06:00 UTC on July 6 as a pinhole eye became evident. Beryl became the second earliest hurricane on record in the Main Development Region (south of 20°N and between 60° and 20°W), behind only a storm in 1933. Simultaneously, the cyclone peaked with 80 mph (130 km/h) and a minimum pressure of 991 mbar (29.3 inHg). Thereafter, increasing wind shear caused it to weaken back to a tropical storm by 12:00 UTC on July 7. A reconnaissance aircraft flight found that Beryl had degenerated into an open trough about 24 hours later. The remnants were monitored for several days. After conditions became more favorable, Beryl regenerated into a subtropical storm near Bermuda at 12:00 UTC on July 14. The rejuvenated storm soon began to lose convection due to dry air intrusion and degenerated into a remnant low once again by 00:00 UTC on July 16. An extratropical storm over Newfoundland absorbed the low on the following day.
In Guadeloupe, four observation sites recorded tropical storm-force winds, downing trees and power lines. Rainfall on the island peaked at 7.8 in (200 mm) in Saint-Claude, causing minor localized flooding due to runoff. Gusty winds in Puerto Rico left approximately 47,000 people without power. Flash flooding closed several road closures and downed several trees. In the Dominican Republic, heavy rainfall led to flooding that displaced more than 8,000 people and isolated 19 communities. Overall, the flooding damaged 1,586 homes and destroyed 2 others. Roughly 59,000 electrical customers lost power. Total damage was estimated to be in the millions.