The 2003 Pacific typhoon season was a below-average annual cycle of tropical cyclogenesis in the northwestern Pacific Ocean, exhibiting the development of 45 tropical depressions, of which 21 became named storms; of those, 14 became typhoons. Though every month with the exception of February and March featured tropical activity, most storms developed from May through November. During the season, tropical cyclones affected the Philippines, Japan, China, the Korean Peninsula, Indochina, and various islands in the western Pacific.
The season ran year-round, with the first storm, Yanyan, developing west of the Marshall Islands on January 15. In April, Typhoon Kujira became one of the longest-lasting Pacific typhoons in history and attained climatological records for its unusually early impacts. Typhoon Imbudo in July killed 85 people when it struck the Philippines and China. It was followed soon after by Tropical Storm Koni, which hit the same countries as well as Vietnam. August was a highly active month for tropical cyclogenesis, with five named storms. In September, Typhoon Maemi became the strongest tropical cyclone of the season, with a minimum barometric pressure of 910 mbar (hPa; 26.87 inHg). Maemi later struck South Korea, becoming one of the country's costliest typhoons after causing US$4.8 billion in damage. In October, two typhoons – Ketsana and Parma – existed simultaneously while staying away from land In late November, Typhoon Lupit devastated areas of Yap State in the Federated States of Micronesia. The season closed with the dissipation of a tropical depression east of the Philippines on December 27.
The scope of this article is limited to the Pacific Ocean, north of the equator and west of the International Date Line. Storms that form east of the date line and north of the equator are called hurricanes; see 2003 Pacific hurricane season. Tropical storms formed in the entire northwest Pacific basin are assigned a name by the Tokyo Typhoon Center. Tropical depressions in this basin monitored by the Joint Typhoon Warning Center (JTWC) have the "W" suffix added to their number. 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 (PAGASA). This can often result in the same storm having two names.
Seasonal forecasts TSR forecastsDate Tropicalstorms TotalTyphoons Ref Average (1972–2001) 26.1 16.3 March 5, 2003 26.2 16.6 April 11, 2003 26.7 17.1 May 6, 2003 26.0 16.3 June 10, 2003 25.8 16.1 July 4, 2003 26.3 16.7 August 5, 2003 27.0 17.5 Actual activity ForecastCenter Tropicalstorms Typhoons Ref JMA 21 14 JTWC 23 17 PAGASA 21 14
On March 5, 2003, meteorologists from the University College London at the Tropical Storm Risk (TSR) Consortium issued a forecast for the typhoon season, noting the likelihood of near average tropical cyclone activity as a result of projected neutral sea surface temperatures. The forecast indicated the potential for 26.2 tropical storms, compared to the 10– and 30-year average of 27.8 and 26.3 storms, respectively. The following month, the group raised their forecast for tropical storms to 26.7, indicating a slightly above average season. Over next two months, however, fluctuations in sea surface temperatures, particularly those in the Central Pacific, caused the group to revise their predictions downward and indicated the probability for a slightly below average typhoon season in their June forecast. A rise in sea surface temperatures in the following months prompted the forecasting group to once again raise their forecasts to indicate a near-average season in their final August forecast update, which predicted 27 tropical storms. The group was very accurate in their forecasts, with their April and August forecasts being the most accurate.
Similarly, meteorologists working with the City University of Hong Kong issued a seasonal projection on April 24, 2003, indicating the likelihood of a normal or below normal season with 29 total tropical cyclones, 26 tropical storms, and 16 typhoons. As with the TSR, the group primarily based their forecast numbers on the prevailing status of the El Niño-Southern Oscillation. The City University of Hong Kong revised their forecasts on June 24, 2003, indicating a slight increase of total tropical cyclones to 30. The group was also accurate in their forecasts for the entirety of the Northwest Pacific, though their specialized forecasts for the South China Sea were substantially off.
During the year, the Japan Meteorological Agency (JMA) issued advisories on tropical cyclones west of the International Date Line to the Malay Peninsula, and north of the equator; this was due to the agency's status as the official Regional Specialized Meteorological Center, as designated by the World Meteorological Organization in 1989. The JMA issued forecasts and analyses four times a day, beginning at 00:00 UTC and continuing every six hours. The JMA issued forecasts based on a climatological tropical cyclone forecast model. The agency estimated 10 minute sustained winds and barometric pressure based on the Dvorak technique and numerical weather prediction. The JTWC also issued warnings on storms within the basin, operating from Pearl Harbor in Hawaii to represent the interests of the United States Armed Forces in the Indian and Pacific Oceans.
Season summary
The Accumulated Cyclone Energy (ACE) index for the 2003 Pacific typhoon season as calculated by Colorado State University using data from the Joint Typhoon Warning Center was 337.4 units. Throughout the season, sea surface temperatures within the western equatorial Pacific were above normal, including those in the South China Sea. Areas of convection persisted year-round in the lower latitudes, particularly around the Philippines. Atmospheric divergence was also prevalent in the same regions, resulting in enhanced tropical cyclogenesis east of the Philippines in 2003; the mean region of development of tropical systems during the year was more southwest than the 1971–2000 30-year average. In 2003, the JMA monitored 21 tropical cyclones of at least tropical storm intensity; of those, 14 reached typhoon intensity. Though the number of tropical storms was below average, the ratio between tropical storms and typhoons was 66% greater than normal. The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) monitored one tropical depression and one tropical storm that were not monitored by the JMA.
Systems Tropical Storm Yanyan
On January 11, a tropical disturbance originated near the International Date Line. Steered by a subtropical ridge to its north, the system tracked westward and developed into a tropical depression on January 15, west of the Marshall Islands. The convection, or thunderstorms, waxed and waned. The JMA upgraded the depression to Tropical Storm Yanyan on January 18, stimating peak 10 minute winds of 65 km/h (40 mph). The JTWC estimated 1 minute winds of 95 km/h (60 mph). Around that time, the storm stalled east of the Mariana Islands and curved sharply northeastward into a less favorable environment. The JMA downgraded Yanyan to tropical depression status on January 20, before reclassifying the system as extratropical cyclone. Strong wind shear decoupled the low-level circulation center from the convection. On January 21, both the JTWC and JMA discontinued the monitoring of Yanyan.
Typhoon Kujira (Amang)
A tropical depression formed on April 9, which moved westward. It strengthened into Tropical Storm Kujira on Apil 11, which attained typhoon status three days later. Late on April 15, Kujira reached its peak intensity with winds of and a minimum barometric pressure of 930 mbar (hPa; 27.46 inHg). Afterward, the typhoon's intensity fluctuated as it passed east of the Philippines and Taiwan, with eventual weakening as it turned to the north. On April 24, Kujira was downgraded to tropical depression strength as it made landfall on Kyushu. Afterward, Kujira transitioned into an extratropical cyclone on April 25, which persisted until crossing the International Dateline.
Shortly after developing, Kujira caused two fatalities in Pohnpei in addition to minor agricultural and infrastructural damage; similar effects were felt in Guam.b Kujira was the first typhoon since 1978 to prompt typhoon warnings in Taiwan. It brought significant rainfall to the island. Effects from the typhoon were most significant in Japan, particularly in the Ryukyu Islands. Strong winds, rain, and waves caused US$230,000 (¥27.8 million) in agricultural damage on Ishigaki Island. One person was killed due to injuries resulting from the waves. In Kyushu, heavy rainfall, peaking at in Ōita Prefecture, was reported.
Typhoon Chan-hom
A tropical depression formed on May 19 to the southwest of Chuuk. A day later, it strengthened into Tropical Storm Chan-hom while moving generally to the north, steered by a shortwave trough. On May 23, Chan-hom attained typhoon status, as it developed an eye. That day, Chan-hom reached peak winds of and a minimum pressure of . Chan-hom began to intake dry air beginning on May 25, resulting in weakening as it accelerated to the northeast. Increased wind shear striped convection from the center. Early on May 27, Chan-hom transitioned into an extratropical cyclone, which dissipated south of the Aleutian Islands the following day.
As a tropical storm, Chan-hom caused some damage to homes and crops on Chuuk, mostly due to heavy rains brought forth by the storm. Offshore, a 1,040 ton fishing vessel, the Nien Feioch, sank during the storm. The ship was valued at $16 million. Winds from the typhoon fanned volcanic ash from the recently erupting Anatahan volcano towards Guam, prompting precautionary measures. Ashfalls were reported on the island, forcing the cancellation of several flights.
Severe Tropical Storm Linfa (Chedeng)
A tropical depression formed off the western coast of Luzon on May 25, quickly strengthening into Tropical Storm Linfa. The storm executed a small clockwise loop before hitting Luzon on May 27. Linfa weakened over land before restrengthening over open waters. It reached its peak intensity on May 29 with maximum sustained winds of and a barometric pressure of 980 mbar (hPa; 28.94 inHg). Linfa transitioned into an extratropical cyclone on May 30, which moved through Japan and later dissipated in the Sea of Okhotsk on June 4.
The erratic and slow movement of Linfa off the western Philippines was the catalyst for extreme rainfall and flooding, killing 41 persons in the archipelago. Precipitation peaked at near Dagupan. Rising floodwaters resulted in the temporary shutdown of government offices and numerous mudslides. In addition, strong winds caused widespread power outages. Overall damage from Linfa in the Philippines amounted to ₱192.3 million (US$3.65 million). The floods also displaced 8,367 people in 1,686 families and destroyed 178 homes. Linfa and its extratropical remnants later brought torrential rainfall and widespread flooding to Japan, particularly in southwestern regions. Rainfall there peaked at . Flood damage was worst in Kōchi and Tokushima Prefectures, where several buildings were destroyed by floodwater. Other locations in Japan experienced considerable agricultural damage as well as numerous landslides. Overall, Linfa caused roughly $28.2 million in damage, much of which occurred in Japan, though the entirety of deaths associated with the cyclone took place in the Philippines.
Severe Tropical Storm Nangka (Dodong)