The 2010 Atlantic hurricane season was the most active hurricane season since 2005 and the first of three consecutive active hurricane seasons, each with 19 named storms. This well above average activity included 12 hurricanes, equaling the number that formed in 1969. The season officially began on June 1 and ended on November 30, dates that conventionally delimit the period during each year when tropical cyclone formation is most likely. The first cyclone, Alex intensified into the first June hurricane since Allison in 1995. The month of September featured eight named storms. October featured five hurricanes, including Tomas, which became the latest on record in a calendar year to move through the Windward Islands. Activity was represented with an accumulated cyclone energy (ACE) value of 165 units, which was the eleventh highest value on record at the time. The activity in 2010 was heightened due to a very strong La Niña, which also led to an very inactive Pacific hurricane season.
Despite the high number of hurricanes, none hit the United States. However, numerous tropical cyclones affected countries bordering the Atlantic Ocean throughout 2010. Alex caused 52 deaths and up to $1.52 billion (2010 USD) in damage as it struck northern Mexico in June. The next month, Tropical Storm Bonnie struck Florida as a weak cyclone, leaving one dead. Tropical Storm Colin led to one drowning death, and rip currents produced by Tropical Depression Five killed two people. Hurricane Danielle passed east of Bermuda while Earl moved parallel to the East Coast of the United States and into Nova Scotia throughout late August, resulting in 2 and 8 deaths, respectively. In early September, Tropical Storm Hermine caused significant flooding across Texas and killed 8 people. The strongest hurricane of the year, Igor, killed four as it traversed the Atlantic and across Newfoundland. Latin America was badly hit by Hurricane Karl and Tropical Storm Matthew, with 22 and 126 deaths, respectively. In late September, Tropical Storm Nicole produced torrential rainfall from the Caribbean into the U.S. East Coast, resulting in 16 fatalities. Hurricane Paula caused a tourist to drown offshore Cozumel in mid-October, while Hurricane Richard left two dead in Belize later that month. The season concluded with Tomas which caused 35 fatalities along its track through the Caribbean and into the Atlantic.
Seasonal forecasts
Before and during each hurricane season, several forecasts of hurricane activity are issued by national meteorological services, scientific agencies, and noted hurricane experts. 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. According to NOAA, the average Atlantic hurricane season between 1950 and 2005 contained 10.3 tropical storms, 6.2 hurricanes, 2.7 major hurricanes, and an accumulated cyclone energy (ACE) index of 66–103 units. Broadly speaking, ACE is a measure of the power of a tropical or subtropical storm multiplied by the length of time it existed. Therefore, a storm with a longer duration will have high values of ACE. It is only calculated for full advisories on specific tropical and subtropical systems reaching or exceeding wind speeds of 39 mph (63 km/h). Accordingly, tropical depressions are not included in the count. After the storm has dissipated, typically after the end of the season, the NHC re-examines the data and produces a final report on each storm. These revisions can lead to a revised ACE total either upward or downward compared to the original value. The National Oceanic and Atmospheric Administration (NOAA) typically categorizes a season as either above-average, average, or below-average based on the cumulative ACE Index, but the number of tropical storms, hurricanes, and major hurricanes within a hurricane season are occasionally considered as well.
Pre-season forecasts
On December 7, 2009, Tropical Storm Risk (TSR) issued their first extended range outlook for the 2010 Atlantic hurricane season, predicting 13.9 named storms, 7.4 hurricanes, 3.4 major hurricanes, and an ACE index of 135 units. The organization referenced two main factors, slower trade winds across the Caribbean and above-average ocean temperatures across the Atlantic, for an above-average season. Two days later, Colorado State University (CSU) issued their first extended range outlook, projecting 11 to 16 named storms, 6 to 8 hurricanes, 3 to 5 major hurricanes, and an ACE index of 100 to 162 units. The organization stated that although a strong El Niño event was ongoing at the release of their forecast, a continuation of a warm El Niño–Southern Oscillation was unlikely to persist through the hurricane season. On January 27, 2010, The Weather Company (formerly WSI) called for the year to feature 13 named storms, 7 hurricanes, and 3 major hurricanes.
CSU issued a more detailed update on April 7, upping their forecast to 15 named storms, 8 hurricanes, 4 major hurricanes, and an ACE index of 150. More confidence in the weakening of El Niño (and thus lower vertical wind shear) and the continuation of anomalously warm sea surface temperatures across the Atlantic Ocean were cited. Two days later, TSR revised their forecast upward to 16.3 named storms, 8.5 hurricanes, 4 major hurricanes, and an ACE index of 159 units. In their April 21 update, WSI predicted the most active year since the record-breaking 2005 season, with 16 named storms, 9 hurricanes, and 5 major hurricanes. Five days later, North Carolina State University (NCSU) released their only forecast for the season, with 15 to 18 named storms and 8 to 11 hurricanes. TSR largely maintained their forecast for their May 25 release. The next day, TWC/WSI again raised their forecast to 18 named storms, 10 hurricanes, and 5 major hurricanes. NOAA, meanwhile, released their forecast prediction for the 2010 season on May 27. The organization called for an active to extremely active year including 14 to 23 named storms, 8 to 14 hurricanes, and 3 to 7 major hurricanes, referencing a continuation of the active era that began in 1995.
Mid-season outlooks
On the first day of the 2010 Atlantic season, Florida State University's Center for Ocean-Atmospheric Prediction Studies (FSU) released their only predictions, forecasting 17 named storms, 10 hurricanes, and an ACE index of 156 units. The next day, CSU upped their forecast to 18 named storms, 10 hurricanes, and 5 major hurricanes. On June 4, TSR followed suit, with 17.7 named storms, 9.5 hurricanes, 4.4 major hurricanes, and an ACE index of 182 units. The United Kingdom's Met Office (UKMET) released their only prediction for the season on June 17, with the most likely number of tropical storms being 20 and the most likely value of the ACE index being 204 units. On June 23, TWC/WSI once again upped their forecast, noting 20 named storms, 11 hurricanes, and 5 major hurricanes. TSR issued their boldest predictions on July 6, with 19.1 named storms, 10.4 hurricanes, 4.8 major hurricanes, and an ACE index of 203 units.
Following a slightly less active June and July than originally anticipated, TWC/WSI downgraded their number of named storms from 20 to 19 on July 21, but kept their June numbers of 11 hurricanes and 5 major hurricanes untouched. In their final seasonal prediction on August 4, CSU left their June numbers the same, predicting 18 named storms, 10 hurricanes, 5 major hurricanes, and an ACE index of 185 units. That same day, TSR reduced their predictions for their final seasonal outlook, expecting 17.8 named storms, 9.7 hurricanes, 4.5 major hurricanes, and an ACE index of 183 units. On August 5, NOAA announced the official development of La Niña in their last seasonal outlook. The organization lowered the upper bounds of their forecast compared to May due to less early season activity than expected, in all predicting 14 to 20 named storms, 8 to 12 hurricanes, and 4 to 6 major hurricanes. TWC/WSI issued two final forecasts on August 25 and September 22, both expecting 18 named storms and 10 hurricanes. The number of major hurricanes was increased from 5 to 6 in their September update, however.
Seasonal summary
Unlike on the eastern Pacific, which tied 1977 for the least active year in the reliable records, the 2010 Atlantic hurricane season ended as one of the most active in recorded history. It began on June 1 and ended on November 30, dates that conventionally delimit the period during each year when most tropical cyclones form in the Atlantic Ocean. The first system of the season, Hurricane Alex, developed on June 25; the final system of the season, Hurricane Tomas, dissipated on November 7. A total of 21 tropical depressions formed within the basin, of which 19 intensified into tropical storms, 12 intensified into hurricanes, and 5 further intensified into major hurricanes. The year's 12 hurricanes matched 1969 for the third highest count on record, exceeded only by 2005 and 2020. There were more tropical storms in the Atlantic than the West Pacific in 2010, the second such occurrence on record after 2005. Throughout the entire Atlantic tropical cyclone database, 2010 is the only year with more than 10 hurricanes not to feature a hurricane landfall on the United States.
Several factors contributed to exceptional activity. A strong El Niño observed in 2009 rapidly transitioned into a strong La Niña by mid-summer 2010, projecting anomalously low vertical wind shear across the Atlantic Ocean. Ocean temperatures reached record levels across the basin, averaging at 0.82 °C above the 1981–2010 average. Not only did ocean temperatures surpass 2005 to break the record overall, averaged water temperatures across the Main Development Region (MDR) of the Atlantic set monthly records from February to October 2010. This was aided by a strongly negative North Atlantic Oscillation that contributed to weaker trade winds and thus anomalous warming of ocean temperatures in the months leading up to the hurricane season. Lower sea level pressures were prevalent throughout much of the season, trailing only 1955 for the lowest average values across the MDR during the August to October period. In spite of the high number of tropical cyclones, mid-level dry air dominated the tropical Atlantic throughout the peak of the season, perhaps hindering the season from being even more active.
The beginning of the Atlantic season featured Alex, the first hurricane observed in June since Hurricane Allison in 1995. One tropical storm, Bonnie, and a tropical depression formed in the month of July. August featured five cyclones – a tropical depression, tropical storms Colin and Fiona, as well as hurricanes Danielle and Earl (both of which further intensified into major hurricanes). September, the peak period of the Atlantic hurricane season, was its most active month, featuring eight tropical cyclones: tropical storms Gaston, Hermine, Matthew, and Nicole, as well as hurricanes Igor, Julia, Karl, and Lisa. This put the season into a tie with 2002 and 2007 for the most tropical storms to develop in September, a record that stood until it was surpassed in 2020. Igor attained peak winds of 155 mph (250 km/h) on September 15, cementing its status as the most intense storm of the season. Well above-average activity continued into October, with the formation of hurricanes Otto, Paula, Richard, Shary, and Tomas, one hurricane short of the monthly record set in 1870. Tomas persisted into the subsequent month before dissipating on November 7, heralding the end of the season's tropical cyclone activity.
The season's activity was reflected with an ACE rating of approximately 165.5 units, the highest since 2005.
Systems
Hurricane Alex
A disturbance developed within the Intertropical Convergence Zone on June 17 and remained well defined as it tracked westward. An area of low pressure developed in association with the system over the northwestern Caribbean on June 24 and further organized into a tropical depression by 18:00 UTC the following day, supported by data from a reconnaissance aircraft. Steered west and eventually west-northwest by an expansive ridge across the Bahamas and Gulf of Mexico, the depression intensified into Tropical Storm Alex at 06:00 UTC on June 26 and attained an initial peak with winds of 65 mph (105 km/h) before moving ashore near Belize City, Belize several hours later. Alex maintained tropical storm intensity as it crossed the Yucatán Peninsula, and upon executing a northward turn and a second westward turn began to steadily intensify. The cyclone intensified into the season's first hurricane at 00:00 UTC on June 30 and attained peak winds of 110 mph (175 km/h) as it made landfall near Soto la Marina, Mexico, at 02:00 UTC on July 1. Once inland, Alex turned west-southwest and rapidly weakened over the mountainous terrain of Mexico. The increasingly disrupted system dissipated at 06:00 UTC on July 2.
The precursor disturbance to Alex flooded hundreds of homes and prompted the evacuation of thousands of residents in the Dominican Republic. Damage to crops and hundreds of structures occurred across Central America. In southern Mexico, torrential rainfall led to numerous landslides and mudslides, while swollen rivers flooded many homes and roads were collapsed. Near the track of Alex in northern Mexico, rainfall reached as high as 35.04 in (890 mm) in Monterrey, 13-foot (4.0 m) waves affected the coastline, hundreds of thousands of citizens lost power, and widespread infrastructure was damaged or destroyed. Although the hurricane did not directly move ashore the coastline of the United States, its spiral bands produced tropical storm-force sustained winds across the southern reaches of Texas, peaking at 51 mph (82 km/h) in Port Isabel. Heavy rainfall broke accumulation records, a storm surge of at least 3.5 ft (1.5 m) caused beach erosion, and embedded supercells produced nine tornadoes (all rated EF0). Along its track, Alex was responsible for 51 deaths (22 missing) and $1.52 billion in damage.