The 2009 Pacific typhoon season was a below average season that spawned only 22 named storms, 13 typhoons, and five super typhoons. Despite this, it was a very deadly season, with the Philippines having experienced its deadliest season in decades due to the impact of typhoons Ketsana and Parma, while typhoon Morakot went on to become the deadliest storm to impact Taiwan in its modern history. The first half of the season was very quiet, whereas the second half of the season was extremely active. During August, Typhoon Morakot devastated Taiwan, killing nearly 800 people and being known for being the deadliest typhoon to impact the country. Typhoons Ketsana and Parma both affected the Philippines, bringing extreme flooding that killed more than 1400 people in total. Typhoon Nida during late November reached 1-minute winds of , which is the most intense in the basin since Typhoon Paka in 1997. The season ran throughout 2009, though most tropical cyclone tend to develop between May and November. The season's first named storm, Kujira, developed on May 3, while the season's last named storm, Nida, dissipated on December 3.

The scope of this article is limited to the Pacific Ocean to the north of the equator between 100°E and 180th meridian. Within the northwestern Pacific Ocean, there are two agencies which assign names to tropical cyclones which can often result in a cyclone having two names. The Japan Meteorological Agency (JMA) will name a tropical cyclone if it has 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 are active in the Philippine Area of Responsibility (PAR), 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 TSR forecastsDate Tropicalstorms TotalTyphoons IntenseTCs ACE Average (1965–2008) 26.6 16.7 8.6 300 March 16, 2009 25.6 16.0 6.7 247 May 7, 2009 27.5 17.6 9.1 319 July 6, 2009 28.0 18.1 10.3 359 August 4, 2009 26.0 18.2 10.6 367 Other forecastsDate ForecastCenter Period Systems January 4, 2009 PAGASA January–December <19 tropical cyclones March 18, 2009 HKO January–December 5–6 tropical cyclones April 20, 2009 GCACIC January–December 31 tropical cyclones June 18, 2009 GCACIC January–December 30 tropical cyclones June 30, 2009 CWB January–December 24–27 tropical cyclones May 1, 2009 VNCHMF January–December 6> tropical cyclones 2009 season ForecastCenter Tropicalcyclones Tropicalstorms Typhoons Actual activity: JMA 39 22 13 Actual activity: JTWC 30 24 15 Actual activity: PAGASA 22 12 8 During each season, 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 include the Tropical Storm Risk (TSR) Consortium of the University College London, Guy Carpenter Asia-Pacific Climate Impact Centre of the City University of Hong Kong (GCACIC) and Taiwan's Central Weather Bureau.

On January 4, PAGASA reported that they were expecting 19 or less tropical cyclones to affect the Philippines during 2009. During March, the TSR Consortium released their first forecast of the season and predicted that activity within the basin would be about 20% below normal with 25.6 tropical storms, 16 typhoons and 6.7 intense typhoons and an ACE index of around 247. Later that month the Hong Kong Observatory, predicted that the typhoon season in Hong Kong would be near normal with five to six tropical cyclones passing within of the territory compared to an average of 6. During April, the GCACIC issued its first seasonal forecast for the year and predicted that the season would see activity near its average with 31 tropical cyclones, 27 tropical storms, and 18 typhoons occurring during the season. The GCACIC also predicted that 4 tropical cyclones would make landfall on Southern China between April and August compared to an average of 3, they also predicted that no tropical cyclones would make landfall between August and December. On May 7, TSR increased its forecast to 27.5 tropical storms, 17.6 typhoons, 9.1 "intense" typhoons and an ACE index of about 311 units, after La Niña conditions weakened and confidence grew that La Niña conditions would not return during 2009. Later that month the Vietnamese National Center for Hydro Meteorological forecasts predicted that six or more tropical cyclones would affect Vietnam during 2009.

During June, the GCACIC reported that the total number of tropical cyclones had decreased from 31 to 30, and that the total number of typhoons had increased to 19, while there was no change to the number of tropical storms predicted to occur during the season. They also predicted that 3 tropical cyclones would make landfall on Southern China between July and December compared to an average of 4. On June 30, the Taiwan Central Weather Bureau predicted that the season would see activity near its average of 26.6, and predicted that between 24 – 27 tropical storms would occur over the Western Pacific. The Central Weather Bureau also predicted that of the 24-27 tropical storms forecast 3-5 of them would affect Taiwan. In their July and August forecasts TSR upped their prediction for the amount of intense typhoons by one to ten and eleven respectively, whilst predicting the same amount of tropical storms and typhoons. In July and August they also predicted that the season would now see activity about 20% above normal. After their initial prediction was surpassed by Tropical Depression Tino forming, PAGASA announced that they expecting two or three more cyclones to affect the Philippines, before the end of the year.

Season summary

The season started with Tropical Depression Auring east of the Philippines, which was then followed by Tropical Depression Bising a month later. After 2 months of inactivity, Tropical Depression Crising and Typhoon Kujira forms, and Kujira becoming the first major typhoon of the season, and was followed by the development of Typhoon Chan-hom in the South China Sea, and hit Pangasinan and crossed the Philippines. In mid-June, Severe Tropical Storm Linfa and Tropical Storm Nangka form and hit the Philippines.

It was followed 1 month later by Tropical Storm Soudelor, which passed through the Batanes Strait and headed for China, and followed by Tropical Depression Huaning which hit Taiwan. Typhoon Molave and Tropical Storm Goni head for China, while Typhoon Morakot becomes the most-costliest storm in Taiwanese history. Tropical Storm Etau briefly forms, and followed by Tropical Depression Maka from the Central Pacific basin, while Typhoon Vamco develops into a Category 4 but barely affects any major landmass. Krovanh peaks as a severe tropical storm, while Dujuan heads northeastward, and not affecting any landmass. Tropical Storm Mujigae forms in the South China Sea, which is followed by Typhoon Koppu, which crossed Northern Luzon. Typhoon Ketsana drops record rainfall in the Philippines, and is followed by Typhoon Parma which drops more rainfall to the already saturated Philippines. Typhoon Melor becomes a Category 5 while Nepartak briefly forms as a tropical storm, and Lupit becomes another Category 5 and nearly hits the Philippines before heading northeast. Typhoon Mirinae hits Central Luzon, causing more damages and misery to the Philippines. Tropical Depression Tino and Urduja briefly form, and Typhoon Nida (Vinta) becomes the strongest and final named storm of the season, which is then followed by a weak tropical depression in late December 2009. Due to many typhoons hitting the Philippines, the 2009 Pacific typhoon season was the costliest season for the Philippines on record.

Systems Tropical Depression Auring

Tropical Depression Auring formed as a tropical disturbance late on December 30, 2008, to the southeast of Manila in the Philippines. Over the next few days the disturbance gradually developed before early on January 3, both PAGASA and the JMA, reported that the disturbance had intensified into the first tropical depression of the season with PAGASA assigning the name Auring to the depression. As the depression was moving into a high level of vertical wind shear, it did not develop any further and late on January 5 as the baroclinic zone approached Auring, it was downgraded to a low-pressure area by PAGASA before the JMA followed suit the next day as it was declared as dissipated by the JTWC.

Heavy rain from Auring produced severe flooding in the eastern Philippines. Two people were killed and nine others were left missing. A total of 305 homes were destroyed and another 610 were damaged. In addition, an estimated of rice and of corn were damaged. About 43,851 people were affected by the depression and damages were estimated at PHP  ( USD).

Tropical Depression Bising

Early on February 12, PAGASA reported that a low-pressure area located about to the east of Surigao City in the Philippines had intensified into a tropical depression. During that day the depression gradually moved towards the west with its peak windspeeds estimated at . Early the next morning after the depression had made landfall on Dinagat Island, PAGASA released its final advisory as the depression had weakened into an area of low pressure.

An estimated 473 passengers and several vehicles were stranded in Liloan and Ormoc due to ferry cancellations. In Cebu, an estimated 1,600 passengers were also stranded due to the depression. Late on February 13, the remnants of Bising brought scattered rainshowers across Southern Luzon, Bicol Region, and Visayas, then dissipated. The rainfall led to mudslides on Cebu Island which blocked the Cebu Transcentral Highway.

Tropical Depression Crising

On April 29, the JTWC reported that an area of deep convection had persisted near the center of an elongated low-level circulation center, in area of low vertical windshear, about , to the west of Manila in the Philippines. Deep convective banding was curving into an eastern southern edges of the disturbance. During the day the disturbance gradually consolidated further under the influence of an anticyclone, as a result of this the JTWC issued a Tropical Cyclone Formation Alert on the system. Early the next morning PAGASA upgraded the disturbance to a tropical depression and named it as Crising as it reached its 10-minute peak windspeeds of . Later that day the JTWC reported that Crising's low-level circulation center has weakened and was now poorly organized as it underwent a Fujiwhara effect with what was to become Typhoon Kujira (Dante). PAGASA kept issuing advisories on Crising until it weakened into a low-pressure area early on May 1.

Heavy rains produced by the outer bands of Crising caused flooding in western areas of the Philippines, affecting an estimated 2,500 people. The worst flooding occurred in Lucena City where ten villages were isolated. Areas along the Bucon and Inalmasinan Rivers were inundated and sustained significant crop losses. Several animals reportedly drowned in the region. Several roads were impassable due to landslides or were washed out by floodwaters. One bridge was destroyed in the town of Mercedes.

Typhoon Kujira (Dante)