2015 Atlantic hurricane season

The 2015 Atlantic hurricane season was the last of three consecutive below average Atlantic hurricane seasons. It produced twelve tropical cyclones, eleven named storms, four hurricanes, and two major hurricanes. The Accumulated Cyclone Energy (ACE) for the season was 68% of the long-term median value. The hurricane season officially began on June 1, 2015, and ended on November 30, 2015. These dates historically describe the period each year when most tropical cyclones form in the North Atlantic basin. However, the first named storm, Ana, developed on May 8, nearly a month before the official start of the season, the first pre-season cyclone since Beryl in 2012 and the earliest since Ana in 2003. The formation of Ana marked the start of a series of seven consecutive seasons with pre-season activity, spanning from 2015 to 2021. The season concluded with Kate transitioning into an extratropical cyclone on November 11, almost three weeks before the official end.

Although most of the storms impacted land, overall effects were minimal. Ana caused minor flooding and wind damage in the Carolinas and left two dead in North Carolina. Tropical Storm Bill and its remnants caused flooding primarily in the South Central, Midwestern, and Mid-Atlantic regions of the United States, while its precursor also left flooding in Central America and Mexico. The storm resulted in two deaths in Honduras, two in Guatemala, one in Mexico, and three deaths in the United States. Additionally, the United States suffered at least $100 million (2015 USD) in damage. Claudette and Danny left very minimal impact on land. In late August, Tropical Storm Erika brought heavy rainfall to Dominica, leading to devastating floods. Erika caused nearly $500 million in damage and 30 fatalities, making it, at the time, the island's deadliest natural disaster since Hurricane David in 1979. The storm also flooded other nearby islands, but to a much lesser degree, such as Guadeloupe, Puerto Rico, and Hispaniola. Five additional deaths occurred in Haiti.

Fred prompted a hurricane warning for Cape Verde for the first time ever and was the first storm to pass through the islands as a hurricane since 1892. Strong winds there left about $2.5 million in damage. Two deaths were presumed to have occurred after two fishermen never returned to port. Seven other sailors likely drowned offshore Guinea-Bissau after their fishing boat collapsed. Tropical storms Grace, Henri, and Ida left negligible impact on land. Hurricane Joaquin's intensity and slow movement in the vicinity of the Bahamas resulted in severe damage on some islands. Additionally, the American cargo ship went missing near Crooked Island and eventually capsized during the storm, drowning 33 people. Rough seas in Haiti also caused damage and one death from a fisherman drowning. Joaquin was the most intense satellite era tropical cyclone of non-tropical origins. The remnants of Kate affected the British Isles, particularly Wales in the United Kingdom. Throughout the season, these storms collectively caused $813.9 million in damage and 89 deaths.

With the exception of Tropical Storm Risk's initial season prediction in December 2014, all major forecasting agencies called for a below or near-average season, due to the strong 2014–16 El Niño event and colder than average sea surface temperatures. Overall, the forecasts were fairly accurate.

Seasonal forecasts

In advance of, and during, each hurricane season, several forecasts of hurricane activity are issued by national meteorological services, scientific agencies, and noted hurricane experts. These include forecasters from the United States National Oceanic and Atmospheric Administration (NOAA)'s National Hurricane and Climate Prediction Center, Tropical Storm Risk, the United Kingdom's Met Office, and Philip J. Klotzbach, William M. Gray and their associates at 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. According to NOAA and CSU, the average Atlantic hurricane season between 1981 and 2010 contained roughly 12 tropical storms, six hurricanes, three 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 or stronger intensity 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 . Accordingly, tropical depressions are not included here. After the storm has dissipated, typically after the end of the season, the NHC reexamines 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 operational value. 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 considered occasionally as well.

Pre-season forecasts

On December 9, 2014, Tropical Storm Risk (TSR), a public consortium consisting of experts on insurance, risk management, and seasonal climate forecasting at University College London, issued its first outlook on seasonal hurricane activity during the 2015 season. In its report, the organization forecast activity about 20% below the 1950–2014 average, or about 30% below the 2005–2014 average, totaling to 13 (±4) tropical storms, 6 (±3) hurricanes, 2 (±2) major hurricanes, and a cumulative ACE index of 79 (±58) units. This forecast was largely based on an enhancement of low-level trade winds across the tropical Atlantic during the July to September period. TSR's report stressed that uncertainty in this forecast existed due to the unpredictability in the El Niño–Southern Oscillation and North Atlantic sea surface temperatures.

A few months later, on April 9, 2015, TSR updated its report, detailing its prediction of activity 45% below the 1950–2014 average, or about 50% below the recent 2005–2014 average, with 11 named storms, 5 hurricanes, 2 major hurricanes, and a cumulative ACE index of 56 units. TSR cited what were expected to be cooler than average ocean temperatures across the tropical North Atlantic and Caribbean Sea as reasoning for lower activity. In addition, the report stated that if the ACE forecast for 2015 were to verify, the total values during the three-year period from 2013 to 2015 would be the lowest since 1992–1994, signalling a possible end to the active phase of Atlantic hurricane activity that began in 1995.

On April 9, CSU also released its first quantitative forecast for the 2015 hurricane season, predicting 7 named storms, 3 hurricanes, 1 major hurricane, and a cumulative ACE index of 40 units. The combination of cooler than average waters in the tropical and subtropical Atlantic, as well as a developing El Niño predicted to reach at least moderate intensity, were expected to favor one of the least active seasons since the mid-1990s. The probabilities of a major hurricane striking various coastal areas across the Atlantic were lower than average, although CSU stressed that it only takes one landfalling hurricane to make it an active season for residents involved. On April 13, North Carolina State University (NCSU) released its forecast, predicting a near record-low season with just 4 to 6 named storms, 1 to 3 hurricanes, and 1 major hurricane.

On May 21, the United Kingdom Met Office (UKMO) issued its forecast, predicting a season with below-normal activity. It predicted 8 storms, with a 70% chance that the number of storms would be between 6 and 10; it predicted 5 hurricanes, with a 70% chance that that number would fall in the range of 3 to 7. UKMO's ACE index prediction was 74 units, with a 70% chance of the index falling in the range of 40 to 108 units. On May 27, NOAA released its seasonal forecast, predicting a below-normal season with 6 to 11 named storms, 3 to 6 hurricanes, and 0 to 2 major hurricanes. NOAA indicated that there was a 70% chance of a below-normal season, a 20% chance of a near-normal season, and a 10% chance of an above-normal season.

Mid-season outlooks

On June 1, CSU released an updated forecast, increasing the number of predicted named storms to 8, due to the early formation of Tropical Storm Ana, while keeping the predictions for hurricanes and major hurricanes at 3 and 1, respectively; the ACE index forecast was also kept at 40 units. Probabilities of a major hurricane making landfall on various coastal areas remained below average. CSU's third forecast, issued on July 1, remained unchanged. The fourth and final forecast issued by CSU on August 4 again predicted eight named storms and one major hurricane, but the number of hurricanes was decreased to two. On August 5, TSR updated their forecast and lowered the number of hurricanes developing within the basin to 4, with only 1 forecasted to be a major hurricane. The ACE index was also reduced to 44 units.

Seasonal summary

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The Atlantic hurricane season officially began on June 1, 2015. It was a slightly below average season in which twelve tropical cyclones formed. Eleven of the twelve designated cyclones attained tropical storm status. Of the eight tropical storms, four reached at least Category 1 hurricane intensity. The 2015 season extended the period without major hurricane landfalls in the United States to ten years, with the last such system being Hurricane Wilma in 2005. The lack of activity was primarily attributed to an atmospheric circulation that favored dry, sinking air over low latitudes to the west of 40°W and westerly wind shear enhanced by El Niño. A few notable events occurred during the season. Ana was the first tropical cyclone to form in the off-season since 2012. Erika became only the second storm in the satellite era to be retired without reaching hurricane strength (Tropical Storm Allison was the first) and only the third to be retired without having made landfall ( Hurricanes Klaus and Fabian were the first and second, respectively). Fred was one of the easternmost tropical storms recorded and made landfall in Cape Verde as a Category 1 hurricane, becoming the first hurricane to strike that country since 1892. Joaquin was the most intense storm of non-tropical origin in the satellite era and the strongest to affect the Bahamas in October since 1866. The tropical cyclones of this season caused 89 deaths and at least $731.8 million in damage. The Atlantic hurricane season officially ended on November 30, 2015.

Tropical cyclogenesis began early, with Ana developing on May 8, over three weeks prior to the official beginning of the season and far ahead of the long-term climatological average of July 9. The month of June featured one tropical cyclone, Bill, which formed on June 16. Claudette, the only system in the month of July, developed on July 13. The rate of tropical cyclogenesis increased in August, though no storms developed in the first half of the month. Danny, the season's first major hurricane, formed on August 16, followed by Erika on August 24, and Fred on August 30. September, which is the climatological peak of hurricane season, featured five additional tropical cyclones – Grace, Henri, Tropical Depression Nine, Ida, and Joaquin. The most intense storm of the season was Joaquin, which peaked as a strong Category 4 hurricane with maximum sustained winds of , just short of Category 5 on the Saffir–Simpson hurricane wind scale. Joaquin lasted into October, though no other systems developed that month. The season's final cyclone, Kate, developed on November 8 and became extratropical on November 11. The season's activity was reflected with an Accumulated Cyclone Energy (ACE) rating of 63, which was well below the 1981–2010 median of 92.

Systems

Tropical Storm Ana

A low-pressure area of non-tropical origins developed into Subtropical Storm Ana at 00:00  UTC on May 8, while situated about 175 miles (280 km) southeast of Myrtle Beach, South Carolina. The system was classified as subtropical due to its involvement with an upper trough, as well as its large wind field. Throughout the day, convection progressively increased as Ana moved north-northwestward across the warm sea surface temperatures associated with the Gulf Stream. At 00:00 UTC on May 9, the cyclone attained its peak intensity with maximum sustained winds of 60 miles per hour (95 km/h) and a minimum barometric pressure of . Six hours later, Ana transitioned into a fully tropical system. However, the storm soon began weakening after moving away from the warm waters of the Gulf Stream and increasing wind shear also contributed to the deterioration of Ana. Around 10:00 UTC on May 10, the system made landfall near North Myrtle Beach, South Carolina, with winds of . Ana weakened to a tropical depression just eight hours later and transitioned into a remnant low near the Delmarva Peninsula at 00:00 UTC on May 12. The remnant low merged with a frontal system about 24 hours later.

Striking South Carolina on May 10, Ana became the earliest U.S. landfalling system on record. In the state, a storm surge peaking at about resulted in erosion and minor coastal flooding, with roads washed out at North Myrtle Beach. Inland, moderate rainfall caused a lake to rise above its bank, inundating some homes and streets. One drowning death occurred in North Carolina after rip currents caused a man to remain underwater for more than 10 minutes. Rainfall in the state peaked at southeast of Kinston, North Carolina, where minor street flooding took place. In Lenoir County, local firefighters rescued several stranded individuals by boat when rising floodwaters isolated about 10 residences. Tropical storm-force winds were confined to coastal areas, with a peak gust of observed near Southport. An additional death occurred in North Carolina after a tree fell on a car in Richlands.

Tropical Storm Bill

The National Hurricane Center (NHC) began monitoring an area disorganized convection across the northwestern Caribbean Sea in association with an upper-level trough on June 12. After interacting with a broad area of low pressure near the Yucatán Peninsula, an elongated area of low pressure formed in the vicinity on June 13. The system moved northwestward into the Gulf of Mexico and developed a well-defined circulation on early June 16. Because the system was already producing tropical storm force winds, it was immediately classified as Tropical Storm Bill while situated about from the US. Initially continuing northwestward, Bill re-curved west-northwestward later on June 16. Around 12:00 UTC, the storm peaked with winds of and a minimum pressure of . Just under five hours later, Bill made landfall near on Matagorda Island, Texas, at the same intensity. The cyclone weakened to a tropical depression and turned northward early on June 17. However, possibly due to the rare brown ocean effect, Bill remained a tropical cyclone until late on June 18, when it degenerated into a remnant low over eastern Oklahoma. The remnant low moved east-northeastward until dissipating over West Virginia on June 21.

The precursor to Bill produced widespread heavy rain in Central America. In Guatemala, flooding affected more than 100 homes while a landslide killed two people. Two others died in Honduras due to flooding with two more missing. Heavy rains fell across parts of the Yucatán Peninsula, with accumulations peaking at in Cancún, the highest daily total seen in the city in nearly two years. One person died from electrocution in the city. In Texas, flooding was exacerbated by record rainfall in some areas in May. A number of roads were inundated and several water rescues were required in Alice and San Antonio. Major traffic jams occurred in the Houston and Dallas areas. Coastal flooding left minor damage, mostly in Galveston and Matagorda counties. One death occurred when a boy was swept into a culvert. In Oklahoma, numerous roads were also inundated by water. Interstate 35 was closed near Turner Falls