2015 Pacific typhoon season

A season shaped by El Niño

The number of storms in 2015 was close to normal, but their strength was not. The Joint Typhoon Warning Center counted 29 cyclones forming in the basin, against a long-term average of 31, yet nine of them reached super typhoon strength. The archive's accumulated cyclone energy of 417.5 reflects how many storms were both intense and long-lived.

The main driver was a strong El Niño. Its sea surface temperature anomalies stayed above 2 degrees Celsius from September onward and reached about 3 degrees Celsius in December. A burst of westerly winds in early March helped build the event and also contributed to the formation of Tropical Storm Bavi. As is typical in El Niño years, the usual genesis region shifted east, so many storms formed near the Marshall Islands and Micronesia and had long stretches of warm ocean ahead of them.

Forecasters anticipated an active year. Tropical Storm Risk predicted 27 tropical storms and an energy index of 400 in May, then raised its outlook to 30 tropical storms and 448 in August, both well above its long-term average of about 26 storms and 294. In Guam, the National Weather Service expected record numbers of major typhoons and of storms affecting Micronesia.

A storm in every month

Activity began early and never fully stopped. Typhoon Mekkhala formed south of Chuuk in mid-January and crossed the central Philippines, interrupting Pope Francis's visit on January 17. Typhoon Higos followed in February, and March brought Tropical Storm Bavi through the Marshall and Mariana Islands before Typhoon Maysak became a Category 5 storm on March 31. Tropical Storm Haishen formed in April, and May produced two more Category 5 typhoons, Noul and Dolphin. A named storm formed in every calendar month, which the season article describes as the first time since 1965.

After Tropical Storm Kujira in the South China Sea in June, the basin turned very busy in early July. Typhoons Chan-Hom, Linfa and Nangka were all active at once, with each heading for a different land area: eastern China, Luzon and southern China, and Japan. Typhoon Halola then crossed the date line from the central Pacific in mid-July.

August and September carried the peak of the season. Soudelor, Goni and Atsani all became major typhoons within the first three weeks of August, and Goni and Atsani were active side by side. Kilo crossed from the central Pacific at the start of September, followed by Etau, Vamco, Krovanh and Dujuan. October brought Mujigae, Choi-Wan, Koppu and Champi, and the year closed with Typhoon In-Fa in November and Typhoon Melor in December. A weak tropical depression drifting across the date line on December 31 was the last tropical system in the archive.

Because so many storms formed far to the east, they lasted a long time over water. The Joint Typhoon Warning Center issued a likely record 1,193 warnings across its area of responsibility in 2015 and twice tracked four cyclones at the same time.

The strongest storms

Typhoon Soudelor was the strongest storm of the season, reaching one-minute sustained winds of 155 knots and a central pressure of 907 hPa in the archive on August 3, over the Philippine Sea after it had struck Saipan. The Japan Meteorological Agency, using ten-minute winds, estimated a lower pressure of 900 hPa.

Four other typhoons reached Category 5. Maysak peaked at 150 knots on March 31, which the season article describes as the most intense cyclone on record in the basin before April. Noul and Dolphin each peaked at 140 knots in May, and Atsani matched that on August 19 far from land. Just below them, Nangka reached 135 knots in July, while Higos, Dujuan and Koppu each reached 130 knots. Higos's February peak made it the strongest February typhoon on record at the time, a mark later surpassed by Typhoon Wutip in 2019.

Notable landfalls and impacts

Micronesia bore an unusual share of the season. Maysak damaged most homes in Chuuk and caused four deaths in the Federated States of Micronesia, with losses of about US$8.5 million in 2015 dollars. Nangka damaged Majuro in the Marshall Islands in July, and Dolphin passed between Guam and Rota in May, leaving 40 percent of Guam without power. Soudelor struck Saipan on August 2, damaging or destroying hundreds of homes. The Joint Typhoon Warning Center counted seven cyclones affecting Guam and the Northern Mariana Islands during the year, along with three typhoons affecting Okinawa and three landfalls on mainland Japan.

Taiwan and China took several heavy blows. Soudelor crossed Taiwan on August 7 and 8, cutting power to 4.85 million households, then brought deadly floods and landslides to eastern China, where economic losses were estimated at 24.627 billion yuan, about US$3.97 billion in 2015 dollars. Chan-Hom came ashore southeast of Shanghai in July after more than 1.1 million people were evacuated. Dujuan crossed northern Taiwan and Fujian in late September, and Typhoon Mujigae intensified rapidly over the South China Sea before striking Zhanjiang in early October. The season article credits Mujigae with 29 deaths and more than US$4 billion in damage in 2015 dollars, including a deadly tornado.

The Philippines faced a string of storms. Typhoon Koppu, known locally as Lando, reached super typhoon strength over very warm water in the Philippine Sea and struck the eastern Philippines in October, causing at least 55 deaths and at least US$230 million in damage in 2015 dollars. In December, Typhoon Melor, known as Nona, came ashore in Eastern Samar and moved slowly through the central islands. The national disaster agency reported 42 deaths and 6.46 billion pesos, about US$136 million, in infrastructure and agricultural damage, and President Benigno Aquino III declared a state of national calamity.

Japan was hit by Nangka, which made landfall in Kochi Prefecture on July 16, and by Tropical Storm Etau in September. Etau itself was modest in strength, but it brought record rain to eastern Honshu, including 668 millimeters at Nikko in Tochigi Prefecture. Floods forced nearly 3 million people from their homes, killed eight and caused about 11.7 billion yen, or US$97.8 million, in damage. Earlier, Tropical Storm Kujira caused flooding in Hainan and northern Vietnam in June, where at least nine people died, and Tropical Storm Vamco killed 11 people in Vietnam in September.

How the counts compare, and retired names

Agency totals for 2015 differ from the archive counts because they measure different things. The archive counts storms by one-minute winds from US agencies, and it lists only storms that formed west of the date line, so Halola and Kilo, which crossed from the central Pacific, are not among its 26 tropical storms. The Joint Typhoon Warning Center counted 28 tropical storms and 21 typhoons, which match the archive's figures once those two storms are added. The Japan Meteorological Agency, using ten-minute winds, counted 27 tropical storms and 18 typhoons including Halola and Kilo. It did not name Tropical Depression 12W, which briefly reached tropical storm strength in one-minute winds, and it kept Mekkhala, Linfa and Choi-Wan below typhoon strength. The season article's energy index of 462.9, calculated by Colorado State University from JTWC data, also differs from the archive's 417.5 because of these differences in coverage.

After the season the Typhoon Committee retired the names Soudelor, Mujigae, Koppu and Melor because of the deaths and damage they caused, replacing them with Saudel, Surigae, Koguma and Cempaka. The Philippine weather agency also retired Lando and Nona, the local names for Koppu and Melor, because each caused more than 1 billion pesos in damage there. The season was also the first to use the names Atsani, Champi and In-Fa.