Typhoon Mireille, named Rosing by PAGASA, was the costliest typhoon on record, until it was surpassed by Typhoon Doksuri in 2023. Striking Japan in September 1991, it became the 20th named storm of the 1991 Pacific typhoon season, Mireille formed on September 13 from the monsoon trough near the Marshall Islands. It moved westward for several days as a small system, steered by the subtropical ridge to the north. The storm rapidly intensified to typhoon status on September 16, and several days later passed north of Saipan in the Northern Marianas Islands. Mireille intensified further after deleterious effects from a nearby tropical storm subsided. On September 22, the American-based Joint Typhoon Warning Center (JTWC) estimated maximum 1-minute sustained winds of , and on the next day, the official Japan Meteorological Agency (JMA) estimated 10‑minute sustained winds of . The typhoon weakened slightly while turning northward, passing just east of Miyako-jima and later to the west of Okinawa. On September 27, Mireille made landfall near Nagasaki in southwestern Japan with winds of , the strongest since Typhoon Nancy in 1961. The storm accelerated to the northeast through the Sea of Japan, moving over Hokkaido before becoming extratropical on September 28. The remnants of Mireille continued to the east, passing through the Aleutian Islands of Alaska on October 1.
The typhoon first threatened Guam, although it passed well to the north of the island, bringing damaging winds to northern Saipan. The first part of Japan affected was Miyako-jima, where heavy rainfall and high winds damaged crops. Mireille lashed Okinawa with strong waves, while strong winds up to damaged power lines and trees. The typhoon ultimately caused damage in 41 of 47 prefectures of Japan, with overall damage estimated at $10 billion (1991 USD, $22.5 billion in 2023), making it the costliest typhoon on record at the time. Mireille produced record wind gusts at 26 locations, with a peak gust of in western Honshu. The winds caused record power outages across Japan that affected 7.36 million people, or about 13% of total customers. Mireille also left extensive crop damage totaling $3 billion, mostly to the apple industry, after 345,000 tons of apples fell to the ground and another 43,000 were damaged on the trees. The storm damaged over 670,000 houses, of which 1,058 were destroyed, and another 22,965 were flooded. Throughout Japan, Mireille killed 66 people and injured another 2,862 people, including ten deaths on a capsized freighter. Elsewhere, the typhoon killed two people in South Korea, and its remnants brought strong winds to Alaska.
Meteorological history
The origins of Mireille were from a poorly-organized area of convection, or thunderstorms, associated with the monsoon trough near the Marshall Islands on September 13. That day, the Japan Meteorological Agency (JMA) began tracking the system as a tropical depression. The system moved westward, developing a large increase in thunderstorms over the center on September 15. That day, the Joint Typhoon Warning Center (JTWC) issued a tropical cyclone formation alert, and issued their first advisory on Tropical Depression 21W at 00:00 UTC, estimating 1-minute sustained winds of . About six hours later, the agency upgraded the depression to Tropical Storm Mireille, after satellite imagery indicated the storm was very compact and intensifying quickly. The JTWC later determined in a post-storm analysis that Mireille had attained tropical storm status 12 hours earlier on the previous day. Also at the time of it attaining tropical storm status, Mireille was one of three storms in the basin, along with Tropical Storm Luke to the northwest and Typhoon Nat to the west in the South China Sea.
Only 12 hours after the JTWC issued the first warning, Mireille attained typhoon status at 12:00 UTC on September 16, and several hours later reached an initial peak intensity of . The small storm moved west-northwestward due to the influence of the subtropical ridge to the north. On September 17, the track shifted to the west-southwest, threatening Guam. The small typhoon turned more to the west, passing about north of Saipan on September 19, part of the Northern Marianas Islands north of Guam. For several days, Mireille failed to intensify due to wind shear from the larger Tropical Storm Luke to the north. After Luke weakened and progressed northward, Mireille was able to strengthen more gradually, as well as increase in size. On September 22, the typhoon strengthened into a super typhoon, which is an unofficial category used by the JTWC for storms reaching 1‑minute winds of at least , equivalent to a strong Category 4 hurricane on the SSHWS. According to the JMA, Mireille attained 10‑minute winds of on September 23.
Around the time of reaching peak intensity, Mireille turned more to the northwest along the southwestern periphery of the subtropical ridge. The increasing size began to impart wind shear in Typhoon Nat to the west, and the two storms underwent the Fujiwhara effect, in which Nat turned sharply southward while Mireille progressed toward the Ryukyu Islands of Japan. After maintaining peak winds for about 30 hours, Mireille began weakening, passing just east of Miyako-jima on September 26 with 10‑minute winds of , according to the JMA. That day, the typhoon accelerated to the northeast due to increasing mid-level winds from the southwest, passing west of Okinawa. According to the JMA, Mireille re-intensified slightly on September 27 to a secondary peak of , aided by unusually warm water temperatures in the East China Sea. The typhoon made landfall at that strength at 07:00 UTC between Saikai and Nagasaki along southwest Kyushu. The pressure at landfall was , the lowest in the country since Typhoon Trix in 1971.
The typhoon quickly weakened while continuing northeastward through Kyushu and western Honshu, and started to become an extratropical cyclone; during the process, the wind field expanded, aided by moist air from the southwest and cold air from the northwest. It accelerated further over the Sea of Japan, and late on September 27, Mireille made a second landfall in Japan along southwestern Hokkaido at 22:00 UTC, with 10‑minute winds of still at typhoon status. Crossing the island, the typhoon weakened to tropical storm status early on September 28, and shortly thereafter became fully extratropical in the Sea of Okhotsk. The powerful remnants of Mireille continued eastward, crossing the Aleutian Islands on September 29 and crossed the International Date Line shortly thereafter. That day, a pressure of was observed in the Pribilof Islands of Alaska. Powerful winds battered vessels in the region, with the Merchant Pride reporting peak sustained winds of . After crossing the dateline, Mireille's remnants turned northeast and struck the Seward Peninsula on October 3 before moving over Arctic Alaska. The system then moved over the Arctic Ocean where it was last noted on October 4.
Preparations and impact Early tropical cyclone computer models anticipated Mireille would pass close to Guam, prompting officials to undergo preparations for the storm. The storm ultimately passed north of Saipan, causing damage along the island's northern portion. Mireille knocked over trees and damaged over 70% of Saipan's crops while also eroding coastal roads.
In South Korea, two people were killed with two others reported missing. A South Korean freighter rode out the storm at the port in Hakata Bay. It breached along the breakwater, causing it to sink, killing all 10 crew members. The Japan Coast Guard launched a search and rescue mission for two days.
Later, the remnants of Mireille moved through the Aleutian Islands toward the end of September, bringing strong winds to the islands, including gusts over at Amchitka.
Japan Ahead of the storm, the JMA issued 99 typhoon bulletins, warning residents about Mireille. There were 236 warnings related to storm surge, high winds, waves, and flooding. In Hiroshima, most residents were aware of the approaching storm, about 70% of residents did not expect significant effects. In general, residents were unprepared for the storm, partly due to the lack of recent storms. Transportation in Japan was disrupted after 480 domestic flights cancelled, stranding 58,000 individuals, and road, rail, and ferry traffic was halted. In Hokkaido, 207 schools were closed due to the storm.
Mireille was the strongest typhoon to hit Japan since Typhoon Nancy in 1961, causing heavy damage in 41 of 47 prefectures. It was the third storm to strike Japan in two weeks. Damage was heaviest on Kyushu where the storm made landfall. Because the storm moved northeastward through the Sea of Japan, the eastern quadrant of the storm crossed over much of the country, which is where the strongest winds in tropical cyclones are located. The high winds downed trees, damaged roofs, and left record power outages, affecting 7.36 million people, or about 13% of total customers. In some areas, the power outages lasted as little as three minutes. The storm damaged over 670,000 houses, of which 1,058 were destroyed, and another 22,965 were flooded. Power outages caused at least five factories to shut down production. Along the coast, the typhoon damaged 930 ships, with dozens sunk or blown ashore. Most of the damage was related to agriculture or forests. Sea spray heavily damaged fruit trees and rice paddies. Crop damage amounted to $3 billion, mostly to the apple industry, after 345,000 tons of apples fell to the ground and another 43,000 were damaged on the trees. Most farms lost 80% of their crop, potentially taking 10 years to regrow. Persistent cloudiness and rainfall following the storm diminished sunlight by 50%, furthering crop damage. There were 62 deaths in Japan and 2,862 injuries, including the deaths on the South Korean freighter, making it the deadliest typhoon there in 10 years. About 80% of the deaths were male, and 70% were over 60 years old. Most of the deaths were related to wind-blown debris, falling due to the wind, or being trapped or struck by fallen objects. The $6 billion in insured losses and $10 billion in overall damage made Mireille the costliest typhoon on record as of January 2015, according to Munich Re.
When Mireille moved through western Japan, it brought strong winds and heavy rainfall. The highest sustained wind was at Nomozaki, Nagasaki, and gusts nearby peaked at . Misawa Air Base along northern Honshu reported winds of at least for five hours, with a peak gust of . This was the highest wind report at the station since records began in 1946. The strongest wind gusts occurred concurrently with a sudden drop in atmospheric pressure, primarily from Kyushu and extending east-northeastward into the Chūgoku region of Honshu. Mireille produced record wind gusts at 26 locations and record sustained winds at 12 locations. At landfall, Mireille produced winds of at least across a diameter of . About two-thirds of the wind stations reported the strongest winds from the west after Mireille passed the area. Winds were lightest in eastern Honshu, Mireille also dropped heavy rainfall, mostly on Shikoku, peaking at at Kito, Tokushima. In nearby Kōchi Prefecture, the heaviest hourly rainfall total was , the highest in the nation for the storm. The rains caused at least 13 landslides and flooded rivers in four locations. However, effects from rainfall were limited due to the storm's fast forward motion. Mireille also struck around the time of high tide, causing extensive storm surge along the coast.