2017 Pacific typhoon season

Season overview

By the number of systems, 2017 was a busy year in the western North Pacific, but its storms were weaker than usual. The Joint Typhoon Warning Center warned on 33 tropical cyclones, two more than its 25-year mean, with an above-average count of tropical depressions and tropical storms but a below-average count of typhoons and super typhoons. The season's accumulated cyclone energy was 164.9 in the site's archive, and the season article rates the year below average by that measure. It was also the first season since 1977 in which no typhoon reached Category 5 strength.

Ocean conditions help explain the pattern. Sea-surface temperatures in the central Pacific kept cooling after the strong 2015 El Niño. The equatorial Pacific stayed ENSO-neutral from January to September, and a weak La Niña developed late in the year. The monsoon trough reached east only to about 140°E, so formation shifted west: 24 of the 33 cyclones tracked by the Joint Typhoon Warning Center formed mainly west of 135°E, with fewer forming out in the open Pacific than in a typical neutral year. That western bias kept many storms short-lived and close to land.

Agency counts differ because they measure different things. The site counts 26 tropical storms and 13 typhoons using US one-minute sustained winds during the tropical stage, which matches the Joint Typhoon Warning Center's own totals. The Japan Meteorological Agency, which uses ten-minute winds, named 27 storms and ranked 11 of them as typhoons. It named Guchol, which peaked at only 30 kt in the US data, and ten-minute averaging generally gives lower wind speeds than one-minute averaging. The Philippine agency PAGASA counted only the 22 systems in its own area of responsibility.

Storm activity through the year

The first half of the year was quiet. A tropical depression near Mindanao in early January brought deadly flooding to the Philippines without reaching storm strength, and Tropical Storm Muifa, the first named storm, formed near Guam in late April and stayed away from land. No storm formed in May, and Tropical Storm Merbok came ashore near Shenzhen in mid-June. In early July, Typhoon Nanmadol crossed the Ryukyu Islands and struck Kyushu. In the US one-minute data it briefly reached 65 kt on July 3, making it the site's first typhoon of the year. By the Japan Meteorological Agency's ten-minute winds it remained a severe tropical storm, so its official first typhoon was Noru on July 23, the latest first typhoon since 1998.

Activity took off in the middle of July. Tropical Storm Talas formed in the South China Sea on July 14, and seven storms developed between late July and early August. On July 29, the remnants of Sonca, Haitang, Nesat and Noru were all active at once. Three of these summer storms, Noru, Kulap and Nalgae, formed unusually far north, above 25°N and east of 140°E. The Joint Typhoon Warning Center linked them to an extensive band of easterly flow and to exceptionally weak cross-equatorial flow during July and August.

August brought the season's most destructive landfalls on the South China coast, as Typhoon Hato and Tropical Storm Pakhar followed each other into the region within days. Typhoon Sanvu and Tropical Storm Mawar followed at the turn of the month. September was calmer, with Typhoon Talim heading for Japan and Typhoon Doksuri striking Vietnam. October brought a deadly tropical depression in northern Vietnam, then Typhoon Khanun and Typhoon Lan. As La Niña took hold in November, most storms tracked west into the Philippines and Vietnam. That pattern continued in December with Tropical Storm Kai-Tak and Typhoon Tembin, whose last tropical-stage observation on December 25 closed the site's record for the season.

Strongest storms

Typhoon Noru is the season's strongest storm on the site, peaking at 135 kt with a minimum pressure of 922 hPa on July 30. It formed as a weak subtropical system near 26°N, 160°E on July 19. It then looped for several days while interacting with Tropical Storm Kulap, and a burst of explosive intensification took it to Category 4. A shifting subtropical ridge carried it on a meandering track for more than 17 days before it recurved near Kyushu and crossed Honshu into the Sea of Japan. The Joint Typhoon Warning Center noted that both its own forecasts and the model consensus struggled with the track. It is also the season's longest-lived storm in the archive.

Typhoon Lan matched Noru's 135 kt and 922 hPa on October 21 in the site's archive. It was the only other super typhoon in the Joint Typhoon Warning Center's count. The Japan Meteorological Agency ranks Lan as the year's strongest storm on the strength of its lower ten-minute pressure estimate. Three more storms reached major typhoon strength of 96 kt or more: Typhoon Talim peaked at 120 kt on September 14, Typhoon Banyan at 110 kt over the open ocean in mid-August, and Typhoon Hato at 100 kt on August 23 as it approached the Pearl River Delta. Typhoon Doksuri came close at 95 kt before its landfall in Vietnam.

Notable landfalls and impacts

Typhoon Hato was the costliest storm of the season. Hong Kong raised its highest warning signal, Hurricane Signal No. 10, for the first time since 2012. In Macau, high tides pushed floodwater into low-lying streets and underground car parks, and 12 people died. In total, 24 deaths were attributed to the typhoon. Reported losses reached about US$4.34 billion in mainland China, US$1.55 billion in Macau and US$511 million in Hong Kong, all in 2017 US dollars. A few days later, Tropical Storm Pakhar struck the same coast, and 12 deaths were linked to it.

Vietnam was struck repeatedly. Tropical Storm Talas killed 14 people there in July. Days later, Tropical Storm Sonca came ashore in Quảng Trị, and its rain caused floods in northeastern Thailand that killed 23 people. Typhoon Doksuri struck Quảng Bình in September, killing 15 people in Vietnam and causing about US$720 million in damage. In October, a tropical depression caused the worst flooding of the year in northern and north-central Vietnam, with 100 deaths and about US$572 million in damage. In November, Typhoon Damrey struck Khánh Hòa as Da Nang prepared to host the APEC summit. At least 112 deaths were reported, and damage topped US$1 billion. All figures are reported deaths and damage in 2017 US dollars.

The Joint Typhoon Warning Center counted five cyclones affecting mainland Japan and one affecting Okinawa. Typhoon Nanmadol's rain, with the stormy weather that lingered after it, was blamed for 41 deaths. Typhoon Noru came ashore while weakening and caused about US$100 million in losses. Typhoon Talim reached Kyushu as a tropical storm on September 17, killing 5 people and causing about US$750 million in damage. Typhoon Lan brought the heaviest losses to Japan in October, with 17 deaths on the mainland and total economic losses estimated at US$2 billion. All figures are in 2017 US dollars.

The Philippines suffered most at the end of the year. Tropical Storm Kai-Tak caused flooding in the central Philippines in mid-December, swamping 80 of Tacloban's 130 villages. The disaster agency confirmed 83 deaths and about US$74.3 million in infrastructure and agricultural damage. Typhoon Tembin followed days later and became the season's deadliest storm. A ferry sank in rough seas, killing five people, and flooding and landslides on Mindanao killed 261 more, 135 of them in Lanao del Norte. Damage was estimated at about US$42 million in 2017 US dollars.

Retired names and other records

The names Hato and Lan were used for the first time in 2017, replacing Washi and Vicente. After the season, the ESCAP/WMO Typhoon Committee retired Hato, Kai-Tak and Tembin because of the deaths and damage they caused, replacing them with Yamaneko, Yun-yeung and Koinu from 2019. PAGASA also retired its local names Urduja and Vinta, used for Kai-Tak and Tembin, after each caused more than ₱1 billion in damage.

The site's archive holds 34 tracks for the year. That is more than the 33 cyclones the Joint Typhoon Warning Center warned on, because it includes one brief system with no wind estimate that is left out of the counts. The Japan Meteorological Agency tracked 41 tropical depressions, several of them weak systems that neither US agency data nor the site's storm counts include. The remnants of Tropical Storm Kirogi went on to help form Cyclone Ockhi in the North Indian Ocean.