The 1984 Pacific typhoon season had the second-latest start in the basin on record, only behind the previous year, 1983, by one day. Despite this, it was above average in terms of named storms and featured many intense storms. It ran year-round in 1984, but again all tropical cyclones formed between June and November. These dates conventionally delimit the period of each year when most tropical cyclones form in the northwestern Pacific Ocean. A total of 44 tropical depressions formed this year, of which only 27 became tropical storms and were assigned a name by the Joint Typhoon Warning Center. This made the season above average when compared to the long term mean of 25 storms per season. Additionally, tropical depressions that enter or form in the Philippine area of responsibility are assigned a name by the Philippine Atmospheric, Geophysical and Astronomical Services Administration or PAGASA. This can often result in the same storm having two names. This year, a total of 20 storms were named this way.
Of the 27 tropical storms, 16 reached typhoon intensity, and two reached super typhoon strength. Eight tropical cyclones moved into mainland China, four struck Vietnam, four moved through the Philippines, and one cyclone moved into South Korea. The second consecutive typhoon season with a late start, all of the season activity was contained between June and December, with August and October the most active months, contributing to half of the seasonal tropical cyclone count.
Season summary
Despite its late start, a total of 30 tropical depressions formed this year in the Western Pacific, of which 27 became tropical storms. A total of 16 storms reached typhoon intensity, of which 2 reached super typhoon strength. Three of the systems formed in June, four in July, seven in August, four in September, eight in October, three in November, and one in December. Eight tropical cyclones moved into mainland China, four struck Vietnam, four moved through the Philippines, and one cyclone moved into South Korea. The most damaging and deadly typhoon this season was Ike, which led to significant damage and two-thirds of the overall seasonal death toll, mainly from the Philippines. The longest lived cyclone was Bill, which persisted for two weeks during mid November. Despite the eight tropical cyclones moving into China, Hong Kong received only 18 percent of its annual rainfall from tropical cyclones, which was 35 percent below the annual average.
Systems
Tropical Storm Vernon
Tropical Storm Vernon, the first of the year, developed in the South China Sea on June 6. It moved northwest, and then westward in an environment of strong vertical wind shear, Vernon moved inland into Vietnam on June 10. Flooding of rice, sweet potato, and sesame crops in Quảng Nam-Da Nang province was caused by Vernon. Combined with 1983's late formation of Tropical Storm Sarah in June, this is only known time that two consecutive years had their first storm develop as late as June.
Severe Tropical Storm Wynne (Asiang)
The monsoon trough established itself across the South China Sea eastward into the Philippine Sea on June 14. A tropical disturbance formed within this trough on June 16 in the northern Philippine Sea. Moving westward for much of its existence to the south of a narrow subtropical ridge, an upper level high developed over the strengthening low level circulation early on June 19, which became a tropical depression that day. By that evening, the cyclone had strengthened into a tropical storm. Strong upper level ridging over mainland China led to easterly vertical wind shear, which limited intensification. The cyclone passed by the southern coast of Taiwan, which caused slight weakening as it entered the South China Sea. Passing south of Hong Kong, a U. S. Naval ship and Hong Kong both reported winds of 60 knots (110 km/h), with gusts to 82 knots (152 km/h) reported at Tate's Cairn and 70 knots (130 km/h) noted out at sea. Southwest flow to the south of Wynne led to flooding in Luzon, where 100 square kilometres (25,000 acres) of riceland was destroyed. Three fisherman drowned north of Luzon. Late on June 25, Wynne made landfall in China near the Luichow Peninsula, and then entered Gulf of Tonkin, made final landfall in Quảng Ninh Province and weakened rapidly inland.
The lowest sea-level atmospheric pressure observed in Tiên Yên during the storm was 987.8 hPa, recorded at 04:00 (UTC+7) on June 26.
Typhoon Alex (Biring)
On June 28, a surface circulation formed in the Philippine Sea. Development of the system began in earnest on June 30, and a tropical depression had formed early on July 1, with tropical storm status attained later in the day. A ridge to its north eroded, allowing Alex to move north-northwest towards Taiwan. Alex became the first typhoon of the season shortly before moving across the mountainous island. On July 5, extratropical transition of Alex had begun. By late in the day, it was an extratropical cyclone along a frontal zone in the Sea of Japan.
Severe Tropical Storm Betty (Konsing)
Development of this system was slow within the eastern portion of the monsoon trough. By midday on July 2, the disturbance was first noted about 1,020 kilometres (630 mi) southwest of Guam. The system moved northwest for much of its life cycle, initially following Alex and then the southwest side of the subtropical ridge. A broad tropical depression formed on the afternoon on July 5 within the disturbed weather area, weakening as it passed over Luzon. Late on July 7, ship reports indicated the system had become a tropical storm. The cyclone moved within the radar fence of Hong Kong near its peak intensity before making landfall 250 kilometres (160 mi) to its west-southwest during the early afternoon of July 9. Winds gusted to 70 knots (130 km/h) at Green Island. Weakening over the topography of China was rapid thereafter, and the system dissipated by early on July 10.
Typhoon Cary
Initiated by the tropical tropospheric trough (TUTT), an area of convection was first noted southeast of the upper trough in an area with favorable upper level divergence on July 2 near 18N 168E. The disturbance moved west-southwest and evolved into a tropical depression late on July 6 and a tropical storm soon after. The cyclone moved northwest towards a break in the subtropical ridge and reached typhoon status late on July 9 forming a large eye about 55 kilometres (34 mi) in diameter. Rapid development continued for another 12 hours as it slowly moved through the ridge axis. The cyclone turned northeast late on July 10 as it began to be sheared significantly from the northwest. Shearing relented on July 11 allowing the eye to reform, this time 75 kilometres (47 mi) wide. As the typhoon progressed more poleward, increased vertical wind shear and the entrainment of cooler and drier air began its extratropical transition. By late on July 14, Cary had become an extratropical cyclone. The nontropical system then moved westward, eventually dissipating south of Japan.
Typhoon Dinah
For two weeks after Betty and Cary, a high pressure dominated the northwest Pacific, with no sign of a monsoon trough. A cold front dropped into the area from the north, and remained stationary across much of the central North Pacific just north of Wake Island for nearly a week. An area of convection along the tail of the old frontal boundary formed on July 21, and closed off a wind circulation just northwest of Wake Island. Drifting westward, the system did not develop considerably until July 23. By late on July 24, it became a tropical depression. Intensifying while moving west-southwest, the system became a typhoon late on July 25 with a 55 kilometres (34 mi) wide eye.
Meanwhile, Tropical Storm Ed was approaching from the northwest and the ridge north of Dinah moved east, which turned the typhoon northwest. For 48 hours between July 26 and July 28, Dinah and Ed were between 1,165 and 1,670 kilometres (724 and 1,038 mi) from one another, and fujiwhara interaction did impart a slight change onto Dinah's track. On July 27, while the cyclones were at their closest approach, Dinah weakened due to the more dominant outflow from Ed. The westerly shear led to a change in track to the east-northeast for Dinah. On July 28, once the cyclones moved farther apart, Dinah restrengthened rapidly and reached its maximum intensity by noon on July 29. Moving north-northeast around the western fringe of the subtropical ridge, Dinah's motion accelerated, moving close to Marcus Island late that afternoon, causing extensive vegetation damage. The coast guard station on the island sustained US$30,000 in damage (1984 dollars) when sustained winds reached 63 knots (117 km/h), with gusts to 89 knots (165 km/h). Weakening as it continued to move north-northeast, Dinah regained tropical storm status on July 31. Veering more northeast and interacting with a nearby upper trough in the Westerlies, Dinah became an extratropical cyclone late on August 1. The nontropical cyclone moved off the east, eventually crossing the International Date Line.
Typhoon Ed
Ed formed along the tail of a weakening cold front just south of Japan on July 23. It took a day to become detached on satellite pictures, and become a tropical disturbance. On the morning of July 25 a surface circulation had formed and the cyclone became a tropical depression. By July 26, it became a tropical storm. Initially it moved southeast during this period of strengthening as it approached Typhoon Dinah. As a shortwave trough in the Westerlies approached Ed, the cyclone turned north and moved away from Dinah. Ridging built in quickly behind the shortwave, and the cyclone turned west-northwest; a course it would maintain until landfall in mainland China. Strengthening continued, and Ed became an intense typhoon just south of Kyūshū. As it moved across the East China Sea, cooler waters and drier air led to weakening. Late on July 31, Ed made landfall 110 kilometres (68 mi) north of Shang-Hai as a strong tropical storm. Turning northwest after landfall, Ed moved along the Chinese coast and gradually weakened. By late on August 1, it had dissipated as a tropical cyclone. The Korean ship Ishlin Glory sank in the Korea Strait on July 29, which led to one death and 11 others declared missing. The launch of the weather satellite GMS-3 was delayed by this typhoon's passage nearby Japan.
Severe Tropical Storm Freda (Ditang)
The tail end of a trough extending southwest of Dinah west of Guam led to the development of this system. A tropical disturbance formed there on August 2 and developed a surface cyclone in the Philippine Sea later that day. A broad surface cyclone, the system tracked northwest and slowly developed. By late on August 5, it became a tropical depression. During the morning of August 6, it strengthened into a tropical storm while maintaining its broad center and a pair of circulation centers. The new northern center became dominant overnight. The system jumped northwest and quickly moved through the Formosa Straits before striking mainland China very early on August 8. Two died in Taiwan due to Freda. After two days inland, Freda finally dissipated as a tropical cyclone, but its cloud pattern remained identifiable for an additional day or two thereafter.
Tropical Depression 09W (Edeng-Gloring)
A broad surface low formed in the near equatorial trough on August 7 about 1,225 kilometres (761 mi) south of Guam. Moving northwest, the disturbance slowly organized as it moved into the southeast portion of the monsoon trough. On August 10, the low jogged northward for a day towards an upper-level low northwest of Taiwan. Late on August 11, the low became a tropical depression, which was named Edeng by PAGASA and designated 09W by the Joint Typhoon Warning Center. It then moved west-northwest along the northern side of the monsoon trough as a sheared system due to moderate southerly flow aloft. A new circulation center developed, which led to PAGASA renaming the system Gloring as it neared the southern coast of Taiwan. The depression ultimately merged with a low-pressure area over the South China Sea, which would develop into Tropical Storm Gerald.