Three simultaneous hurricanes active on September 8, 2017 – with Katia(left), Irma(center), and Jose(right). All three were threatening land at the time.Taken by various of satellites throughout 2017, these are the 19 tropical cyclones that reached at least Category 3 on the Saffir-Simpson scale during that year, from Enawo in March to Lan in October (though Debbie is out of order). Among them, Maria (fourth image in the third row) was the most intense with a minimum central pressure of 908 hPa.
The most active basin in the year was the Western Pacific, which documented 27 named systems. However, the season had slightly below-average activity, and was the first season since 1977 to feature zero Category 5-equivalent super typhoons forming in the basin. The Eastern Pacific, despite amounting to 18 named systems, which constitutes above-average activity, was also significantly less active than the previous three Pacific hurricane seasons (2014, 2015 and 2016). However, the North Atlantic featured 17 named storms, and was the costliest tropical cyclone season on record. It also had the fifth-most named storms since reliable records began in 1851 – tied with 1936 – and the most major hurricanes since 2005. Activity across the southern hemisphere's three basins—South-West Indian, Australian, and South Pacific—was spread evenly, with each region recording seven named storms apiece, and with the most powerful cyclone, Cyclone Ernie, explosively intensifying to a Category 5 tropical cyclone. Two other Category 5 tropical cyclones formed in the North Atlantic, totalling to three Category 5 tropical cyclones that formed during the year. The accumulated cyclone energy (ACE) index for the 2017 (seven basins combined), as calculated by Colorado State University (CSU) was 621.1 units, which was below the 1981-2010 mean of 770.2 units.[1][2][3]
For the majority of the year, the tropics were dominated by neutral El Niño–Southern Oscillation (ENSO) conditions, before La Niña conditions set in later in the year.[4] As the year opened, sea surface temperatures anomalies across the central and east-central equatorial Pacific were cooler than average, while the impacts of La Niña lingered within the atmospheric circulation, following an abrupt end to the 2016 La Niña episode. Over the next few months, these anomalies warmed and nearly reached the thresholds needed for an El Niño event to be declared, however, they subsequently cooled throughout the rest of the year and the 2017–18 La Niña event was declared to be underway.
The map above shows sea surface temperatures in the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico on September 5, 2017
Scientists pointed out that the increase of CO2 emissions contributes to warmer ocean waters and more moist air for rain.[5] Because of sea level rise it is assumed that the storm surge of Hurricane Irma and other storms will cause greater flooding to vulnerable areas.[6][5] Data collected by NASA showed that ocean surface temperatures in the path of Irma were above 30 °C (86 °F), capable of sustaining a Category 5 hurricane.[7]
Prior to affecting the U.S. mainland, Miami's mayor Tomás Regalado noted on Hurricane Irma, "This is the time to talk about climate change. This is the time that the president and the EPA and whoever makes decisions needs to talk about climate change."[8] A day later the head of the EPA, Scott Pruitt said, "..to discuss the cause and effect of these storms, there's the… place (and time) to do that, it's not now."[9] Following Irma's landfall, Donald Trump was asked about the connection between hurricanes and climate change, and stated that "We’ve had bigger storms than this."[10]Richard Branson who was directly impacted by hurricane Irma noted, "..hurricanes are the start of things to come. Look, climate change is real. Ninety-nine per cent of scientists know it's real. The whole world knows it's real except for maybe one person in the White House."[11]
United Nations secretary general António Guterres citing the devastation from hurricanes noted in September, "The catastrophic Atlantic hurricane season has been made worse by climate change. Cutting carbon emissions must clearly be part of our response to the disaster. The rise in the surface temperature of the ocean has had an impact on weather patterns and we must do everything possible to bring it down."[12]
The Associated Press looked at the yearly average accumulated cyclone energy (ACE), which accounts for wind speed and storm duration to assess hurricane power of the past 30 years and found it to be 41 percent higher than the previous 30 years. They asked several experts about their opinion, James Kossin from NOAA "There's no question that the storms are stronger than they were 30 years ago." Climate scientist Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research, "The only caveat being that the increase might be exaggerated somewhat because of undercounting early storms." Meteorologist Philip Klotzbach noted, "What's happening with hurricanes — the frequency, the duration, and the energy — is probably a combination of factors caused by both nature and man, a mish-mosh of everything."[13] Kerry Emanuel who studies hurricanes, told the BBC, "The warming of the climate has increased the underlying probabilities of very heavy rain events like happened in Harvey and very high category hurricanes like Irma. It is just not sensible to say either storm was caused by climate change, but the underlying probabilities are going up."[14]
The Atlantic basin was hyperactive with 17 named storms, 10 consecutive hurricanes, and 6 major hurricanes. It was also the second consecutive above-average season since 2016 and the costliest season on record. Most of the damage was caused by hurricanes Harvey, Irma, and Maria. Hurricane Nate was considered the worst natural disaster in Costa Rican history. Due to the damage that the four hurricanes made, the names Harvey, Irma, Maria, and Nate were retired by the WMO after the season.[15]
The first named storm, Arlene, formed on April 19 as a subtropical depression. When Arlene was named on April 20, it became only the second named storm to form in April in the Atlantic, the other being Ana in 2003 and the strongest tropical cyclone on record in April. No storms formed in May.
Throughout June and July, activity increased with Tropical Storms Bret, Cindy, Don, and Emily and Tropical Depression Four. Tropical Storm Bret was the earliest named storm to form in the Main Development Region, affecting Venezuela and Trinidad and Tobago. Tropical Storm Cindy also existed throughout mid-June, affecting Louisiana. Together, both caused at least $28 million in damage and five deaths within the areas they affected. In July, tropical depression Four and tropical storms Don and Emily existed with the latter causing widespread floods throughout central Florida. Despite this activity within the first two months, most storms were weak or short-lived and resulted in the lowest ACE for the first five named storms on record, surpassing 1988.[16]
In August, Hurricanes Franklin, Gert, Harvey, and Irma formed with the latter two causing catastrophic damage to the contiguous United States. Hurricane Harvey caused catastrophic flooding and was tied the costliest hurricane on record along with Hurricane Katrina in 2005. Harvey was also the wettest tropical cyclone ever recorded in the United States with a rainfall total of 60.58 inches in Nederland, Texas. Hurricane Irma caused a trail of damage from the Leeward Islands to Florida, causing $77.2 billion in damage, and became the first Category 5 hurricane to make landfall in the Leeward Islands.
In September, copious activity occurred with Hurricanes Jose, Katia, Lee, and Maria, with the latter becoming the tenth most intense hurricane on record. Along with the four systems, Irma also persisted through early September, making it and Maria the first Category 5 hurricanes to occur within the same month. Hurricane Maria caused catastrophic damage to Puerto Rico and Dominica with over 3,000 fatalities and $91.606 billion in damage. Accumulated cyclone energy also increased rapidly during this month, resulting in three hurricanes achieving an ACE over 40, the first on record to do so, September 8 becoming the most active day on record based on ACE, and Hurricane Irma achieving the third-highest ACE on record in the Atlantic with 64.9 units.[17]
By October, activity still persisted although the potential for a La Niña would begin peaking by November. Hurricane Nate became the worst natural disaster in Costa Rican history as a precursor, while Ophelia became the worst tropical cyclone to affect Ireland in 50 years. Philippe was a short-lived system that contributed to a bomb cyclone shortly after its dissipation.
Finally, Tropical Storm Rina became the last storm to form in this basin, dissipating on November 9. The extratropical remnants of this system later contributed to Cyclone Numa (or Storm Zenon), which affected Greece, Italy, France, Tunisia, and Turkey and caused the worst weather event in Greece since 1977. The season ended on November 30.
The 2017 Pacific hurricane season was a moderately active season with eighteen named storms, nine hurricanes, and four major hurricanes. Unlike the three previous hyperactive seasons (2014, 2015, and 2016), the season was significantly less active in terms of ACE and most storms that existed through this basin were either weak or short-lived.
Early May saw the formation of Tropical Storm Adrian, which was the earliest named tropical cyclone to exist east of 140°W at the time; it was surpassed by Tropical Storm Andres in 2021.[18] Throughout June and July, the basin saw some considerable activity, with the latter month having the fifth-highest ACE in the Eastern Pacific.[19] Storms that existed during this time include Hurricanes Dora, Eugene, Fernanda, Hilary, Irwin, Tropical Storms Beatriz, Calvin, and Greg, and Tropical Depression Eight-E, which contributed to the ACE count throughout the earlier parts of the season. Throughout August and September, activity decreased significantly, but stagnated in terms of named storms with some being short-lived. For example, in September, only four named storms formed (Otis, Max, Norma and Pilar) and October featured tropical storms Ramon and Selma, in which none attained hurricane status. Selma became the first named storm to make landfall in El Salvador[20] and also contributed to the formation of Philippe in the Atlantic. No storms have formed in November since 2010.
In the Central Pacific, no storms have formed since 2011. The season began on June 1 and both seasons ended on November 30, 2017.
The 2017 Pacific typhoon season was a below-average season in terms of accumulated cyclone energy and the number of typhoons and super typhoons, and the first since the 1977 season to not produce a Category 5-equivalent typhoon on the Saffir–Simpson scale.
The first half of the season was relatively inactive, with only seven systems developing, of which only two intensified into tropical storms. The first system of 2017 developed on January 7, and was named Auring by PAGASA. Tropical Depression Bising developed during the first week of February, and was a factor in, and worsened the effects of, the 2017 Visayas and Mindanao floods. This was followed by Crising, the third system unofficially named by PAGASA. Heavy rains from the depression caused flooding that led to the deaths of 10 people in Cebu, Philippines. Shortly after the dissipation of Crising came the formation of the first tropical storm of the season – Muifa. The system was not strong, however, and was located away from all major land areas, so it caused no damage. No systems formed during the month of May, the first such occurrence since 2013. The next cyclone, Merbok, formed during mid-June, and made landfall in Shenzhen in China. The cyclone was short-lived; however, it was relatively strong, producing winds of 100 km/h (60 mph) at its peak. Nanmadol passed over the Ryukyu Islands and progressed to make landfall in Nagasaki on Japan's island of Kyushu during early July. Torrential rainfall and strong winds from the cyclone itself and from the stormy weather that persisted for a number of days were responsible for major damage and 41 fatalities across mainland Japan.
By the middle of July, tropical activity had increased with simultaneous tropical storms developing after July 14. Severe Tropical Storm Talas formed during mid-July near the Paracel Islands in the South China Sea, and traveled generally westwards. It made landfall in Vietnam after brushing China's Hainan province and, unusually, continued to track far inland to the Laos–Thailand border before weakening to a depression. At least 14 deaths were attributed to the storm, primarily as a result of flooding. Later, the season was very active with 7 storms in late July-early August. Typhoon Noru reached Category 4 super typhoon in peak intensity and made landfall in Japan, causing $100 million in damage. Tropical Storm Sonca made landfall in Quảng Trị, Vietnam; 2017 was the first year since 1971 where 2 storms made landfall in Central Vietnam in July. Sonca brought heavy rainfall in Northeast Thailand and caused extreme flooding in the region with estimated costs of over US$300 million. Typhoon Nesat and Tropical storm Haitang made landfall in Taiwan and Fujian (a province in China), respectively, 2 days apart. In mid-late August, Typhoon Hato and Tropical Storm Pakhar made landfall in Macau and Guangdong respectively while they were at peak intensity. So far Typhoon Hato is the costliest tropical cyclone in Northwest Pacific in 2017 with damages totalling $6.82 billion.
The season was weaker in September. Typhoon Talim made landfall in Japan as a minimal typhoon and caused US$700 million in damage. Typhoon Doksuri made landfall in Quảng Bình, Vietnam as a Category 3 typhoon; damage was very major as the total was estimated at over US$814 million. In early October a tropical depression made landfall in Northern and North Central Vietnam, which brought very heavy rainfall and was responsible for the worst flooding in Northern and North-Central Vietnam, with 109 deaths and total damages of over US$570 million. Later, Typhoon Khanun made landfall in Southern China. So far Typhoon Lan has been the strongest tropical cyclone in the basin in 2017, and became the second largest tropical cyclone on record.
In November, La Niña was returned and tropical activity had increased with simultaneous tropical storms developing, and most of them moved west and affected Philippines and Vietnam. Typhoon Damrey made landfall in Khánh Hòa, Vietnam and became one of the costliest typhoon in Vietnamese history since 1975; and it is one of the costliest and deadliest typhoon in the basin in 2017 with total damage reached US$1.03 billion and 151 deaths. Later, two weak storms affected Philippines. In December, Tropical storm Kai-tak caused flooding in Central Philippines. Typhoon Tembin was responsible for severe flooding and landslides in South Philippines, it became the deadliest tropical cyclone in 2017 with over 250 deaths. Typhoon Tembin moved South into the China Sea, so 2017 became the most active tropical cyclone season in the South China Sea with 22 Tropical cyclones, and Tembin affected Southern Vietnam.
The 2017 North Indian Ocean cyclone season was a below average yet deadly season in the annual cycle of tropical cyclone formation. This season produced only three named storms, of which one only intensified into a very severe cyclonic storm.
The season officially had an early start compared with the last two seasons, with the formation of Cyclone Maarutha over the Bay of Bengal in mid-April. Cyclone Mora, formed in late May over the Bay of Bengal. At its peak intensity, it was equivalent to a marginal Category 1 hurricane on the Saffir–Simpson hurricane wind scale. The cyclone produced severe flooding across Sri Lanka, India, Myanmar and Bangladesh and caused 15 deaths directly and 208 deaths indirectly. The floods persisted in Bangladesh since a Deep Depression over Bay of Bengal made landfall and killed 156 people in Bangladesh. A depression formed in northwestern Bay of Bengal and produced torrential rainfall. It was followed by a depression over Jharkhand which killed 70 people in West Bengal. Under the influence of strong monsoonsurge a disturbance developed over Bay of Bengal travelled westwards and intensified to an unnamed depression. It also affected neighboring Karachi in Pakistan. A strong monsoon surge prevented formation of systems until a deep depression formed over West Bengal in October and caused heavy rainfall. A couple of depressions formed between mid-October and November which continued the rain spell causing destruction of life and property. Very Severe Cyclonic Storm Ockhi formed in early December and wreaked havoc in the countries where it impacted. It was equivalent to a strong Category 3 hurricane on the Saffir–Simpson scale at peak intensity. The twin storm of Ockhi was a deep depression which originated in Bay of Bengal while its counterpart was in Arabian Sea.
In January 2017, 12 storms formed. Tropical Low 14U, the strongest system this January 2017, affected the Northern Territory and the Western Australia. Surprisingly, 01W (Auring) formed on January 7 on the West Pacific and lasted until the 16th.
In February, 16 systems formed. Cyclone Dineo, one of the deadliest tropical cyclones on record in the South-West Indian Ocean and Southern Hemisphere, hit Mozambique and lasted from February 13 to 17th of the same month. On the West Pacific, Bising formed and lasted from 3rd – 7th of this month.
10 storms formed on April. One notable storm is Cyclone Ernie on Australian Region, is one of the quickest strengthening tropical cyclone on modern record. Crising also formed and affected Philippines in its lifespan.
5 systems formed on May. Tropical Storm Adrian, the earliest-known formation of a named storm in eastern Pacific proper, formed on May 9 and lasted until 10th of this month. Cyclone Donna also formed, which is the strongest Off-season South Pacific Cyclone on the month of May.
23 systems formed on the month of July, making it the busiest month of this year. On the West Pacific, Tropical Storm Nanmadol, Tropical Storm Talas, Typhoon Noru, Tropical Storm Kulap, Tropical Storm Sonca, Tropical Storm Roke (Fabian), Typhoon Nesat, Tropical Storm Haitang (Huaning) and Tropical Storm Nalgae formed. On the East Pacific, Hurricanes Eugene, Fernanda, Hilary and Irwin., a depression and Tropical Storm Greg formed. On the Atlantic, Tropical Storm Don, Tropical Storm Emily, and a weak depression formed. On the North Indian Ocean, two depressions formed.
12 cyclones existed in September 2017. In the Western Pacific, Typhoons Talim and Doksuri, as well as Tropical Storm Guchol and Tropical Depression 22W (Nando) formed. In the Eastern Pacific, Hurricanes Otis, Max, Norma, and Tropical Storm Pilar existed during September. The strongest cyclone of September was Hurricane Maria, which was the second Category 5 hurricane to make landfall in the Atlantic in 2017. Hurricanes Jose, Katia, and Lee also existed in the Atlantic.
14 cyclones existed in October 2017. The strongest tropical cyclone in this month was Typhoon Lan, which was the third most intense tropical cyclone based on central pressure. Along with Lan, Tropical Depression 23W, Tropical Depressions 26W and 29W, Tropical Storm Saola, Typhoons Khanun, and Damrey existed in the Western Pacific. In the Atlantic, Hurricanes Nate, Ophelia, as well as Tropical Storm Philippe existed during the month. In the Eastern Pacific, Tropical Storms Ramon and Selma formed during the month. In the North Indian Ocean, Land Depression 02 and Depression BOB 05 formed during the month.
8 cyclones existed in November 2017. The strongest and deadliest tropical cyclone during this month was Cyclone Ockhi, which affected Sri Lanka, India, and The Maldives, causing 318 deaths and $920 million in damages. Another cyclone that formed in the North Indian Ocean was Depression BOB 06, which also affected Eastern India. In the North Atlantic, Tropical Storm Rina existed and became the last-named storm in the basin. Its remnants eventually led to the formation of Cyclone Numa in mid-November. In the Western Pacific, Tropical Storms Haikui and Kirogi existed during the month, affecting the Philippines and Indochina. In the Australian Region, cyclones Cempaka and Dahlia affected Indonesia and existed during this month.
During the month of December, 11 systems formed within their respective basins. The strongest tropical cyclone of this month is Cyclone Ava, which brought devastating impacts to Eastern Madagascar. The costliest and deadliest tropical cyclones of this month were Typhoon Tembin and Tropical Storm Kai-tak, both of which affected the Caroline Islands, Philippines, Malaysia, and Vietnam throughout their existence. Other tropical cyclones from this month include Tropical Storm Bolaven, which existed throughout January 2018, Cyclone Guará in the South Atlantic, Cyclone Hilda and Tropical Low 05U in the Australian Region, BOB 08 in the North Indian Ocean, and three tropical depressions in the South Pacific.
^The "strength" of a tropical cyclone is measured by the minimum barometric pressure, not wind speed. Most meteorological organizations rate the intensity of a storm by this figure, so the lower the minimum pressure of the storm, the more intense or "stronger" it is considered to be. The strongest winds were actually from Irma, at 180 mph (285 km/h).
1 Only systems that formed either on or after January 1, 2017 are counted in the seasonal totals. 2 Only systems that formed either before or on December 31, 2017 are counted in the seasonal totals. 3 The wind speeds for this tropical cyclone are based on the IMD Scale which uses 3-minute sustained winds.
4 The wind speeds for this tropical cyclone are based on the Saffir Simpson Scale which uses 1-minute sustained winds.
^Podlaha, Adam; Bowen, Steve; Darbinyan, Claire; Lörinc, Michal. "Global Catastrophe Recap – April 2017"(PDF). Aon Benfield Analytics. Archived from the original(PDF) on May 18, 2017. Retrieved June 20, 2017.
^Richard J. Pasch; Andrew S. Latto; John P. Cangialosi (April 2, 2018). Tropical Storm Emily(PDF) (Report). Tropical Cyclone Report. National Hurricane Center. Retrieved April 8, 2018.
