The 2015 Pacific typhoon season was a very active typhoon season that produced twenty-seven tropical storms (including two that crossed over from the Eastern/Central Pacific), eighteen typhoons, and nine super typhoons, as well as an extremely high accumulated cyclone energy (ACE) index of 462.9, which was the third highest since 1970. The 2015 ACE has been attributed in part to anthropogenic warming, and also the 2014-16 El Niño event, that led to similarly high ACE values in the East Pacific. The season ran throughout 2015, though most tropical cyclones typically develop between May and November. The season's first named storm, Mekkhala, formed on January 15, while the season's last named storm, Melor, dissipated on December 17. The season saw at least one named tropical system forming in each of every month, the first time since 1965. Similar to the previous season, this season saw a high number of super typhoons.
The scope of this article is limited to the Pacific Ocean to the north of the equator between 100°E and 180th meridian. Within the northwestern Pacific Ocean, there are two separate agencies that assign names to tropical cyclones which can often result in a cyclone having two names. The Japan Meteorological Agency (JMA) will name a tropical cyclone should it be judged to have 10-minute sustained wind speeds of at least 65 km/h (40 mph) anywhere in the basin, whilst the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) assigns names to tropical cyclones which move into or form as a tropical depression in the Philippine Area of Responsibility (PAR) located between 135°E and 115°E and between 5°N–25°N regardless of whether or not a tropical cyclone has already been given a name by the JMA. Tropical depressions that are monitored by the United States' Joint Typhoon Warning Center (JTWC) are given a number with a "W" suffix.
Seasonal forecasts
During the year several national meteorological services and scientific agencies forecast how many tropical cyclones, tropical storms, and typhoons will form during a season and/or how many tropical cyclones will affect a particular country. These agencies included the Tropical Storm Risk (TSR) Consortium of the University College London, Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) and the Taiwan's Central Weather Bureau. Some of the forecasts took into consideration what happened in previous seasons and the El Niño Conditions that were observed during the year. The first forecast of the year was released by PAGASA during January 2015, within its seasonal climate outlook for the period January – June. The outlook noted that one to two tropical cyclones were expected between January and March while one to three were expected to develop or enter the Philippine Area of Responsibility between April and June.
During March the Hong Kong Observatory predicted that the typhoon season in Hong Kong, would be near normal with four to seven tropical cyclones passing within 500 km (310 mi) of the territory compared to an average of six. Within its Pacific ENSO Update for the 2nd quarter of 2015, NOAA's Pacific El Niño–Southern Oscillation Applications Climate Center, noted that the risk of a damaging tropical cyclone in Micronesia was "greatly enhanced" by El Niño. As a result, they forecasted that the risk of a typhoon severely affecting Micronesia was high, with most islands predicted to have a "1 in 3 chance" of serious effects from some combination of high winds, large waves and extreme rainfall from a typhoon. They also predicted that there was a near 100% chance of severe effects from a typhoon somewhere within Micronesia. On May 6, Tropical Storm Risk issued their first forecast for the season and predicted that the season, would be the most active since 2004 with activity forecast to be above average. Specifically it was forecast that 27 tropical storms, 17 typhoons, and 11 intense typhoons would occur, while an ACE Index of 400 was also forecasted.
Ahead of the Thailand rainy season starting during May, the Thai Meteorological Department predicted that one or two tropical cyclones would move near Thailand during 2015. The first of the two tropical storms was predicted to pass near Upper Thailand in either August or September, while the other one was expected to move to the south of Southern Thailand during November. On June 30, Taiwan's Central Weather Bureau predicted that 28–32 tropical storms would develop over the basin, while two — four systems were expected to affect Taiwan itself. During July, Paul Stanko of the United States National Weather Service Weather Forecast Office in Tiyan, Guam, called for tropical cyclone activity to be above average. He also predicted that several records would be set for the number of major typhoons in the western Pacific, tropical storms, typhoons and major typhoons in Micronesia. PAGASA subsequently predicted within its July — December seasonal climate outlook, that seven to ten tropical cyclones were likely to develop and/or enter the Philippine area of responsibility between July and September, while three to five were predicted for the October–December period. On July 16, the Guy Carpenter Asia-Pacific Climate Impact Centre (GCACIC) and the City University of Hong Kong's School of Energy, released their seasonal forecast for the period between June 1 – November 30. They predicted that 19.9 tropical cyclones would develop during the period with 10.3 of these going on and making landfall compared to averages of 23.0 and 17.4 tropical cyclones. They further predicted that both the Korea — Japan region and that Taiwan and the Eastern Chinese provinces of Jiangsu, Shanghai, Zhejiang, Fujian would see three of these landfalls each. Vietnam, the Philippines and the Southern Chinese provinces of Guangdong, Guangxi and Hainan were forecasted to see four landfalling tropical cyclones. On August 5, Tropical Storm Risk issued their final forecast for the season and predicted that 2015 would be a hyperactive season. Specifically it was forecast that 30 tropical storms, 20 typhoons, 13 intense typhoons would occur, while an ACE Index of 448 was also forecasted.
Season summary
Most of the 27 tropical cyclones affected Micronesia, because of the record-tying 2014–16 El Niño event. 2015 opened with Tropical Depression Jangmi (Seniang) from the previous season active within the Sulu Sea, to the north of Malaysia, on January 1, 2015. The system subsequently moved south-eastward, made landfall on Malaysia, and dissipated later that day. However, the official first tropical cyclone of the season was a minor tropical depression, in the same place where Jangmi persisted on January 2, but dissipated two days later. Tropical Storm Mekkhala, on January 13, developed and approached the Philippines where it caused minor damages and also notably interrupted Pope Francis's visit to the country. In early-February, Typhoon Higos developed further east of the basin and reached peak strength of a Category 4 typhoon. Higos became the strongest typhoon on record in the month of February when it broke the record of Typhoon Nancy (1970), and was in turn surpassed by Typhoon Wutip in 2019. During the opening days of March 2015, a major westerly wind burst occurred, which subsequently contributed to the development of the 2014–16 El Niño event and Tropical Storm Bavi. Typhoon Maysak developed and became the most intense pre-April tropical cyclone on record, with maximum 280 km/h (175 mph) 1-minute sustained winds and a minimum pressure of 910 mbar (27 inHg) at its peak intensity. Only one weak system (Haishen) formed in April, which caused little to no damage.
In May, two storms, Typhoons Noul and Dolphin, both reached Category 5 super typhoon intensity. Both typhoons affected landmasses and altogether caused about $37.1 million in damages, respectively. Kujira formed in June and made landfall in southeast Asia, bringing flooding. During the first week of July, the tropics rapidly became active, with a trio typhoons developing simultaneously and affecting three different landmasses. Total damages from Chan-hom, Linfa and Nangka nearly reached US$2 billion. Afterwards, Typhoon Halola entered the basin from the Eastern Pacific. In August, Typhoon Soudelor made landfall in Taiwan and China, where it killed 38 people and damages totaled up to US$3.7 billion. Typhoon Goni badly affected the Philippines, the Ryukyu Islands and Kyushu as an intense typhoon, causing about US$293 million in damages.
In September, Tropical Storm Etau brought flooding in much of Japan, with damages at least US$100 million. Tropical Storm Vamco made landfall over in Vietnam and caused moderate impact and damages. Typhoon Dujuan, similar to Soudelor, impacted China and Taiwan with total damages of $660 million as a Category 4 super typhoon. In early October, Typhoon Mujigae rapidly intensified into a Category 4 typhoon when it made landfall over Zhanjiang, spawning a tornado causing 29 deaths and over US$4 billion in damages. Later, Typhoon Koppu devastated the Philippines as a super typhoon, causing at least $230 million in damages and killing at least 55 people. Typhoon In-fa became a strong typhoon in November, causing minor impact over in the Caroline Islands. In December, Typhoon Melor maintained Category 4 intensity as it passed the Philippine Islands with 42 deaths and US$140 million in damages, while a tropical depression, named Onyok by PAGASA, made landfall in southern Philippines. The final tropical cyclone of the year developed near Malaysia on December 20, and dissipated three days later.
The Accumulated Cyclone Energy (ACE) index for the 2015 Pacific typhoon season as calculated by Colorado State University using data from the Joint Typhoon Warning Center was 462.9 units, which puts it as the fourth-most intense typhoon season since records began in 1950. Broadly speaking, ACE is a measure of the power of a tropical or subtropical storm multiplied by the length of time it existed. It is only calculated for full advisories on specific tropical and subtropical systems reaching or exceeding wind speeds of 39 miles per hour (63 km/h).
Systems
Severe Tropical Storm Mekkhala (Amang)
Tropical Depression 01W developed during January 13, to the south of Chuuk State. Despite convection being displaced from its exposed low-level circulation center (LLCC), the JMA upgraded 01W to a tropical storm with the name Mekkhala, the first of the season. Later, the PAGASA had stated that Mekkhala had entered the Philippine Area of Responsibility, assigning it the local name Amang. By January 15, the JTWC upgraded Mekkhala to a tropical storm when spiral banding wrapped into a defined LLCC. Mekkhala intensified to a severe tropical storm when deep convection wrapped into its center during January 16. Satellite imagery revealed that a central dense overcast had obscured its center, therefore Mekkhala strengthened into a Category 1 typhoon by the JTWC. Operationally the JMA classified Mekkhala's peak as a typhoon on January 17, however in post-analysis Mekkhala reached its peak as a severe tropical storm. At the time when Mekkhala made landfall over in Eastern Samar, Visayas, land reaction persisted and the typhoon weakened to a tropical storm. By January 18, Mekkhala continued weakening as it started to "unravel and erode" as it passed through the Bicol region in Luzon. Both the JMA and the JTWC issued their final warning later that day. However, the JMA continued to monitor Mekkhala until it dissipated early on January 21.
Mekkhala (Amang) had mostly minor impacts in the Philippines. The storm left 3 dead in total in Bicol region and caused about ₱318.7 million (US$7.13 million) in damages. Moreover, the storm caused agricultural damage of ₱30.3 million (US$678,000) in Samar, where it made landfall. Mekkhala also interrupted Pope Francis's visit to the Philippines on January 17.
Typhoon Higos
During February 6, the JMA started to monitor a tropical depression that had developed about 190 km (120 mi) to the northwest of Palikir in Pohnpei State. By February 7, the JTWC started issuing advisories while designating the system as 02W. Deep convection later deepened over in its LLCC and 02W intensified into a tropical storm, with the JMA naming it as Higos. Higos started to organize as its convection consolidated and its center became well-defined. The JMA upgraded Higos to a severe tropical storm thereafter. With multiple curved bands wrapping to its center, Higos strengthened into a Category 1 typhoon. The JMA upgraded Higos to a typhoon early on February 9. Higos explosively intensified through the course of 24 hours and on February 10, Higos reached its peak intensity with 1-minute sustained winds of 240 km/h (150 mph), making it the first super typhoon of the season. Later, Higos rapidly weakened; its eye dissipated and convection became less organized, so the JMA downgraded Higos to a severe tropical storm. By February 11, Higos further weakened to a tropical storm as its center became fully exposed. Both agencies issued their final warning later that day and Higos fully dissipated on February 12.Higos was the most powerful February typhoon at the time until Typhoon Wutip surpassed it in 2019.