The 2005 Pacific typhoon season was the least active typhoon season since 2000, producing 23 named storms, of which 13 became typhoons (including 4 super typhoons). It was an event in the annual cycle of tropical cyclone formation, in which tropical cyclones form in the western Pacific Ocean. The season ran throughout 2005, though most tropical cyclones typically develop between May and October. The season's first named storm, Kulap, developed on January 13, while the season's last named storm, Bolaven, dissipated on November 20. The season's first typhoon, Haitang, reached typhoon status on July 13, and became the first super typhoon of the year three days later.
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, one from the JMA and one from PAGASA. The Japan Meteorological Agency (JMA) will name a tropical cyclone should it be judged to have 10-minute sustained wind speeds of at least anywhere in the basin, while the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) assigns names to tropical cyclones which move into or form as a tropical depression in their area of responsibility located between 135°E and 115°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 number with a "W" suffix.
Seasonal forecasts
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 included the Tropical Storm Risk (TSR) Consortium of University College London, PAGASA and Taiwan's Central Weather Bureau. Some of the forecasts took into consideration what happened in previous seasons and the La Niña conditions that were observed during the previous year.
On March 14, TSR published their extended range forecast for the 2005 season, in which the anticipated that they would see tropical activity slightly below the average. They predicted that there would be a total of 25-26 tropical storms and 16 typhoons. The TSR, however, forecast that their number of intense typhoons would go slightly above the average, bringing their prediction of 10 intense typhoons. Their main reasons behind this is due to weaker trade force winds occurring in many parts of the basin, and there would be an enhanced cyclonic vorticity over the northwestern part of the Pacific. On April 27, the GCACIC made their first forecast for the season, expecting about 24 tropical storms developing, in which 15 of them would strengthen into typhoons. By May 5, TSR published their first forecast, still predicting a near average typhoon season. Around this time, 27-28 tropical storms, 17-18 typhoons and 9 intense typhoons were predicted, with the slight increase of the number of tropical storms were due to a slight increase in temperatures within the Niño 3.75 region.
TSR's second forecast was released on June 7, now predicting a slightly above average season, with the only change for their predicted cyclone numbers was a slight increase of intense typhoons to 9.4. The GCACIC made their second and final forecast for the season on June 24, slightly increasing their numbers to 25 tropical storms and 16 typhoons. The TSR maintained their predictions after their third forecast update on July 5. Sea-surface temperatures within the Pacific were predicted to be more warmer than that predicted back in the May forecast. On August 5, TSR released their fourth and final forecast for the season, still remaining the same numbers along with the same reasonings.
Seasonal summary
The Accumulated Cyclone Energy (ACE) index for the 2005 Pacific typhoon season as calculated by Colorado State University using data from the Joint Typhoon Warning Center was 309.9 units.