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 season produced a total of 27 named storms, 11 typhoons, and only two super typhoons, making it an slightly above-average season in terms of storm numbers. It was an event in the annual cycle of tropical cyclone formation, in which tropical cyclones form in the western Pacific Ocean. The season runs throughout 2017, though most tropical cyclones typically develop between June and November. The season's first named storm, Muifa, developed on April 25, while the season's last named storm, Tembin, dissipated on December 26. This season also featured the latest occurrence of the first typhoon of the year since 1998, with Noru reaching this intensity on July 23.
The scope of this article is limited to the Pacific Ocean, to the north of the equator between 100°E and the 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. PAGASA assigns unofficial names to tropical cyclones which move into or form as a tropical depression in their area of responsibility, located between 115°E–135°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 numerical designation with a "W" suffix.
Seasonal forecast
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 include the Tropical Storm Risk (TSR) Consortium of University College London, PAGASA, and Taiwan's Central Weather Bureau. The first forecast of the year was released by PAGASA during January 20, 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 two to four were expected to develop or enter the Philippine Area of Responsibility between April and June. On March 23, the Hong Kong Observatory predicted that the tropical cyclone season in Hong Kong would be near-normal, with four to seven tropical cyclones coming within 500 km (310 mi) of the territory, compared to an average of six, which was revised to six to nine tropical cyclones in August.
On May 5, Tropical Storm Risk (TSR) issued their first forecast for the season, anticipating an activity of slightly above normal with 27 named storms, 17 typhoons and 10 intense typhoons, including an accumulated cyclone energy (ACE) of 357. On June 26, Taiwan's Central Weather Bureau (CWB) predicted a normal season with 21–25 tropical storms developing over the basin, while three — five systems were expected to affect Taiwan itself. On the same day, the Thai Meteorological Department (TMD) predicted that 2 tropical cyclones would move towards the northern or northeastern parts of Thailand during August or September. On July 6, TSR released their second forecast for the season, reducing the predicted numbers to 25 named storms, 15 typhoons, and 7 intense typhoons, with an ACE Index of 250. During the same day, the PAGASA issued their second and final outlook for the season for the period of July–December, where six to nine tropical cyclones were expected to develop or entered their area of responsibility between July and September, while three to five were forecast during October to December. During August 8, the TSR released their third and final forecast for the season, slightly raising their forecast named storms to 26, with 14 reaching typhoon intensity and 7 reaching intense typhoon intensity. ACE Indices were slightly raised to 255.
Season summary
The first half of the season was relatively inactive, with only seven systems developing, of which only two intensified into tropical storms. The first tropical depression developed on January 7 and was named Auring by PAGASA. Another 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 to have received a local name from PAGASA. Heavy rains from the depression caused flooding that killed ten people in Cebu, Philippines. Shortly after Crising dissipated, the first tropical storm of the season, Muifa, formed. Since it was not strong and located away from all major land areas, it caused no damage. No systems formed during the month of May, the first such occurrence since 2013. The next named storm, 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. Typhoon Hato was 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. Typhoon Lan was the strongest tropical cyclone in the basin in 2017, going on to strike Japan, causing $2 billion in damages.
In November, La Niña 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.
Systems
Tropical Depression 01W (Auring)
On January 7, both PAGASA and the JMA reported that Tropical Depression Auring developed about 400 km (250 mi) to the northeast of Davao City on Mindanao, Philippines. During that day, the system moved along the southern periphery of a subtropical ridge of high pressure, before the JTWC initiated advisories on the system and designated it as Tropical Depression 01W. It later made landfall in the Philippines the next day, and was assessed to have degenerated into a remnant low by the JTWC. The JMA tracked the system until it emerged into the South China Sea. By January 15, the JTWC re-issued advisories as it was located to the east of Vietnam. However, convection dissipated due to wind shear and land interaction, the JTWC issued their final warnings on January 16.
Flooding from Auring killed a total of 11 people. Damages from Tropical Depression Auring were totaled at ₱7.14 million (US$144,000) from agriculture and fishing in Negros Occidental.
Tropical Depression Bising
On February 3, a tropical depression developed near Palau. The PAGASA would later name it as "Bising" as the depression was present at the Philippine Area of Responsibility. The storm would meander around the Philippine Sea, until the depression started to weaken when its LLCC became exposed, while moving north-northeast. The agency would not notice its weakening until the next day, when they issued their last advisory.
Tropical Depression 02W (Crising)
A tropical depression formed over Palau on April 13. On the next day, the JTWC designated the depression as "02W"; on the best track, the depression was a remnant low at this time. Hours later, the PAGASA would name it "Crising" as the depression was present at the Philippine Area of Responsibility. The depression would later shrink its size while approaching the Visayas region. On the following day, the agency reported that "Crising" slightly intensified while moving near the Samar provinces; the intensification of the storm would prove only momentarily and weakened again. The JTWC would later discontinue advisories on the storm; on its best track, the system remained as a disturbance. The PAGASA discontinued the advisories on the system as it was nearing landfall on 13:00 UTC (9:00 pm PHST) over Hernani, Eastern Samar. The remnants of the depression crossed the region and into the South China Sea. At 18:00 UTC on April 18, the JTWC would upgrade the disturbance as 02W; operationally, the system was kept as a disturbance. The status would be short-lived, as the JTWC declared 02W as a disturbance. The remnants would later linger around, dissipating on April 20, while in the Luzon Strait.
As of April 17, at least 10 people were reported to be killed in Cebu by flooding caused by the system. Total damages throughout the Philippines reached ₱84.8 million (US$1.7 million), mostly from Danao, Cebu.
Tropical Storm Muifa (Dante)
During April 22, the JMA started to monitor a tropical depression that had developed near Guam. After moving westward for a couple of days, the JTWC began issuing advisories, and designated the storm 03W. By April 25, 03W organized and began consolidating further as the JMA upgraded the depression to a tropical storm, giving it the name Muifa. Muifa entered the Philippine Area of Responsibility the following day, and was named Dante by PAGASA. The storm, however, started moving northwards and immediately tracked out of the area by April 27. Following this, both the JMA and the JTWC downgraded Muifa to a tropical depression. Muifa fully dissipated early on April 29, and the JMA issued their final advisory on the storm.
Severe Tropical Storm Merbok
On June 10, the JMA started to track a tropical depression to the west of Manila, Philippines. After the system entered a region favorable for further development, the depression rapidly organized, prompting the JTWC to start issuing advisories and give it the designation of 04W. A few hours later, 04W had intensified into a tropical storm, receiving the name Merbok as it starts to move in a north-northwestward direction. On June 12, Merbok reached its peak intensity with 10-minute winds of 100 km/h (60 mph) and a minimum pressure of 985 hPa, shortly before making landfall in Eastern Shenzhen. On June 13, the JMA issued its final warning on Merbok, as the system dissipated over China.
Sustained winds of 51.3 knots (95.0 km/h; 59.0 mph) and a minimum pressure of 990.3 hPa (29.24 inHg) were recorded in Hong Kong as the eye passed nearby. Across Guangdong Province, 32 homes were destroyed, 122,000 people reported property damage, and 13,000 hectares of crops flooded. Total economic losses in South China were counted to be CN¥600 million (US$88.3 million).