Tropical Storm Merbok (2011)

The 2011 Pacific typhoon season was a below average season that produced a total of 21 named storms, 8 typhoons, and four super typhoons. This season was much more active than the previous season, although both seasons were below the Pacific typhoon average of 26. The season ran throughout 2011, though most tropical cyclone tend to develop between May and October. The season's first named storm, Aere, developed on May 7 while the season's last named storm, Washi dissipated on December 19.

The season was also much deadlier and destructive than the previous season. Typhoon Muifa affected many countries during August. Tropical Storm Talas and Typhoon Roke made landfall over in Japan and were the most destructive since 2009. Typhoon Nesat was the most powerful to strike China since 2005. Tropical Storm Washi, a late but weak cyclone, affected southern Philippines and killed 2546 people.

The scope of this article is limited to the Pacific Ocean to the north of the equator between 100th meridian east and the 180th meridian. Within the Northwestern Pacific Ocean, there are two separate agencies who assign names to tropical cyclones which can often result in a cyclone having two names. The Japan Meteorological Agency will name a tropical cyclone should it be judged to have 10-minute sustained wind speeds of at least anywhere in the basin. Whilst the Philippine Atmospheric, Geophysical and Astronomical Services Administration 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 even if the cyclone has had a name assigned to it by the Japan Meteorological Agency. Tropical depressions that are monitored by the United States' Joint Typhoon Warning Center are given a number with a "W" suffix.

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Seasonal forecasts

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 Guy Carpenter Asia-Pacific Climate Impact Centre (GCACIC), of the City University of Hong Kong, the Tropical Storm Risk (TSR) Consortium of the University College London, and the Taiwan's Central Weather Bureau.

During January 2011, the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) predicted that between twenty and twenty-three tropical cyclones were likely to develop and/or enter the Philippine area of responsibility during 2011. On March 20 the Hong Kong Observatory, predicted that the typhoon season in Hong Kong would be near to above normal with six to nine tropical cyclones passing within of the territory against an average of around 6. On March 30, the TSR Consortium released their first forecast of the season and predicted that the basin would see a near average season with 27.8 tropical storms, 17.5 typhoons, 7.8 "intense" typhoons and an ACE index of about 275. In early April, the China Meteorological Administration (CMA) predicted that between 24 and 26 tropical storms would develop or move into the basin during the year, which it noted was higher than the previous total of 14. They also predicted that between seven and nine tropical storms would make landfall on China, with the first landing taking place before June 29 and the last landing taking place after October 7. On April 26, the Thai Meteorological Department predicted that two tropical storms would affect Thailand during 2011, with one affecting Upper Thailand during August or September, while one was expected to move through Southern Thailand during October or November.

During May within its first outlook for the year, the GCACIC predicted that the season would be near average with 31 tropical cyclones, 27 tropical storms and 17 typhoons developing during the season. They also predicted that seven tropical cyclones would make landfall on Southern China, between May and December, compared with an average of five while predicting that six tropical cyclones during the whole year compared to an average of four tropical cyclones. TSR revised its initial prediction during May and subsequently predicted that 28.0 tropical storms, 17.7 typhoons, 7.6 "intense" typhoons and an ACE index of about 266. In late June after a near-normal start to the season Taiwan's Central Weather Bureau predicted that the season, would be near average of 25.7 with 22–26 tropical storms occurring over the basin during 2011. Between three and five of the systems were predicted to affect Taiwan, compared to an average of around 3.6. Within its July forecast update, the GCACIC predicted that seven tropical cyclones would make landfall on Southern China, between July and December compared to an average of four and that there would now be 16 typhoons due to the strength of the India-Burma trough. They also predicted that seven tropical cyclones would pass within of the Korean Peninsula or Japan, during July and December compared to an average of around three. Within its July update, TSR predicted that the ACE index would be about 194, after raising its prediction for the number of tropical storms to 28.0, typhoons to 18.1 and intense typhoons to 8.4. On August 4, TSR subsequently slightly revised these predictions within its final update for 2011 to 28.2 tropical storms, 17.9 typhoons, 8.0 "intense" typhoons and an ACE index of about 281.

Seasonal summary

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from:01/01/2012 till:05/01/2012

During April two tropical depressions developed but they failed to intensify into tropical storms. Tropical Storm Aere (Bebeng) then developed on May 5, and after causing PHP 2.25 billion in damage to Northeastern Luzon and Eastern Visayas, the name Bebeng was retired by PAGASA. The second tropical storm of the season then developed on May 19, and affected the Philippines, Taiwan and Japan before becoming extratropical to the east of Japan.

After Tropical Storm Banyan dissipated during October 14, no tropical storms or typhoons were observed within the basin until Tropical Depression 27W developed into Tropical Storm Washi during December 15, due to high vertical windshear and a strong northeast monsoon.

Systems

Tropical Depression 01W

On April 1, the JMA reported that a tropical depression had developed within an area of moderate vertical wind shear about to the southeast of Ho Chi Minh City in Southern Vietnam. Over the next day, the system gradually developed further, before the JTWC initiated advisories on the system and designated it as Tropical Depression 01W. However, within hours of this, the depression became devoid of convection as wind shear buffeted the system. This prevented the cyclone from intensifying beyond depression status as it remained nearly stationary. The JMA continued to monitor the system as a tropical depression for another day before issuing their last warning on the system.

Tropical Depression 02W (Amang)

On March 30, the JMA began monitoring an area of low pressure located southwest of Yap. By April 2, the system developed a low-level circulation, though convection appeared disorganized. Exhibiting good outflow within a region of weak wind shear, the low was anticipated to develop further over the following several days as it drifted west-northwestward. After briefly stalling early on April 3, the storm turned towards the east. Additionally, the JMA considered the system sufficiently organized to be declared a tropical depression. As the system was located to the west of 135°E, PAGASA began issuing advisories on the depression as well, assigning it the name "Amang". Tracking northeastward, the depression eventually developed enough convection to be declared Tropical Depression 02W by the JTWC on April 4. However, this was expected to be brief as a decaying frontal boundary approached from the west and prompted the system to undergo an extratropical transition. This intensification prompted the National Weather Service (NWS) in Tiyan, Guam to issue a tropical storm warning for the islands of Agrihan, Pagan and Alamagan. Interacting with the front and high wind shear, the system became partially exposed and elongated as it moved over cooler waters. Early on April 6, the JTWC issued their final advisory on the depression as it began to dissipate over open waters.

Tropical Storm Aere (Bebeng)

On May 3, the JTWC started to monitor a tropical disturbance that had developed within a monsoon trough about to the west of Palau. At this time the disturbances low level circulation center was weak and unorganized, while a minimal amount of deep convection was observed around the system. Over the next couple of days the depression gradually developed further in an area of low vertical wind shear before it was declared a tropical depression by the JMA and the JTWC during May 6. In the same evening, PAGASA upgraded the low pressure into a tropical depression and assigned its local name 'Bebeng'. On the afternoon of May 7, JMA upgraded the depression to a tropical storm and assigned the name 'Aere'. During the early morning of May 12, the JMA downgraded Aere to a tropical depression while south of Kyushu Island as it became a weak extratropical cyclone. It's extratropical remnants finally dissipated on May 15.

Throughout the Philippines, multiple agencies activated their emergency plans as the storm approached. The Armed Forces of the Philippines, the Philippine National Police, and the Philippine Coast Guard were all placed on standby to deploy to areas struck by Aere once the storm passed. Several ports were affected by the storm, stranding 1,379 passengers by the afternoon of May 7. According to the National Disaster Risk Reduction and Management Council, at least 35 people have been killed and two more are missing as a result of Aere. Agricultural losses are estimated at PHP1.37 billion (US$31.7 million). Widespread flooding and landslides damaged homes, blocked off roads and severed communications. In Catarman, Northern Samar, of rain fell in just 24 hours, resulted in significant flash flooding.

Typhoon Songda (Chedeng)

A weak non-tropical system formed within the Intertropical Convergence Zone on May 17, as it moved in a westward direction. On May 19, the JTWC reported that an area of low pressure had persisted about to the southeast of Yap. As the system moved towards the northwest under the influence of a subtropical ridge of high pressure, it rapidly consolidated in an area of light to moderate vertical wind shear. The JMA then started to monitor the system as a tropical depression later that day, before the JTWC designated it as Tropical Depression 04W early on May 20. The JTWC then reported later that day that the depression had intensified into a tropical storm with wind speeds of , however, it later reported that it had overestimated the wind speeds and consequently lowered the storm's status to a tropical depression, based on observations from Yap island. Late on May 21, both the JMA and the JTWC reported that the depression had now become a tropical storm with the JMA naming it as Songda. Over the next couple of days, the system gradually intensified further while moving northwest into PAGASA's area of responsibility. PAGASA named it as Chedeng. At 1200 UTC on May 24, the JTWC reported that Songda had intensified into a typhoon. 12 hours later, the JMA followed suit while the system was located about to the southeast of Manila in the Philippines. It rapidly intensified into a Category 5 typhoon. On the afternoon of May 29, Songda became extratropical south of Shikoku Island. The extratropical remnants of Sonda later crossed the International Date Line, which was later absorbed by another extratropical cyclone on June 4, and later dissipated completely over Alaska.

Although Songda remained offshore, heavy rains within the typhoon's outer bands impacted the Philippines, causing significant flash flooding and landslides. Four fatalities are attributed to the system there. Further north, Okinawa experienced intense wind gusts, measured up to , along with torrential rain. Extensive damage took place across the area with losses reaching ¥23.2 billion ($287 million); however, there were no fatalities. As it became extratropical, Songda brought heavy rains from Kyushu to eastern Honshu, causing significant flooding. At least 13 people were killed in the country and an estimated 400,000 had to be evacuated around Tokyo alone.

Tropical Storm Sarika (Dodong)

On early June 8, an area of low pressure formed about west of Cebu City, Philippines. As it moved towards the Mindoro Strait the JMA and JTWC began to monitor the system. In the early morning hours of June 9, the Philippines' PAGASA upgraded the system to a tropical depression and reported the storm center to be about west of Dagupan in the Philippines. The next day, the JMA and JTWC upgraded the tropical depression into a tropical storm, with the JMA naming it Sarika. During the morning of June 11, the JTWC downgraded Sarika to a tropical depression after making landfall in Shantou, China. The JTWC soon issued their final advisory on Sarika. Sarika made landfall on mainland China with winds of .

As a result of the storm, 23 people were killed in Xianning, and ten more were declared missing. Damages from Sarika are estimated at $248 million.

Tropical Storm Haima (Egay)

Two tropical disturbances formed in an area of convection and moderate vertical wind shear east of Mindanao, Philippines on June 13. Both of them started to interact with each other and the other one absorbed the moisture of the other disturbance. On June 15, the JTWC started to monitor an area of disturbed weather within that disturbance that was located about , to the southeast of Manila, Philippines. Over the next couple of days the system gradually developed further, before late on June 16, the JMA, JTWC and PAGASA, all reported that the system had developed into a tropical depression, with PAGASA naming it as Egay. Egay continued to develop during June 17, as it moved towards the northeast, and on June 18, the JTWC reported that Egay had intensified into a tropical storm. Fluctuations in intensity occurred over the next several days, before the JMA reported that the system had strengthened into a tropical storm on June 22, naming it Haima. The JTWC also followed suit, by upgrading it to a tropical storm again.

During the evening of June 23, the JTWC downgraded Haima to a tropical depression after making landfall in Zhanjiang, Guangdong, China but upgraded it to a tropical storm again on June 24,. Early on June 25, Haima became a tropical depression after moving inland in Vietnam. As it made landfall over Hanoi, Vietnam, the JTWC and the Hong Kong Observatory downgraded Haima to a low-pressure area.

Severe Tropical Storm Meari (Falcon)

Early on June 20, an area of low pressure about , east of the Philippines began to be monitored by both the JTWC and JMA. That evening, the JTWC issued a Tropical Cyclone Formation Alert. Soon afterwards, PAGASA upgraded the system into a tropical depression, naming it as "Falcon". At the time of the upgrade, Falcon was located about , east northeast of Cebu City. During the evening of June 21, the JTWC also reported that Falcon had strengthened into a tropical depression. On June 22, both the JTWC and the JMA upgraded Falcon into a tropical storm, and the JMA named it Meari. Meari left the Philippines with 2 deaths and 5 people missing. On the afternoon on June 24, the JMA upgraded Meari to a severe tropical storm as it passed Okinawa, Japan.

On June 26, Meari rapidly moved to the Yellow Sea but slowly passed Weihai, Shandong, China, and then the JMA downgraded Meari to a tropical storm on the same day. On June 27, the JTWC downgraded Meari to a tropical depression before it made landfall on North Korea, and the JMA reported that Meari became a low-pressure area later.

Heavy rains from the storm's outer bands triggered significant flooding and landslides in South Korea. At least nine people were killed and three others were reported missing across the country. In North Korea, heavy rains from the storm caused widespread flooding and damage. At least 160 homes were destroyed and 50,000 hectares of crops submerged. Several reports of confirmed fatalities arose but no details on how many were given to news agencies.

Tropical Depression Goring

Late on July 8, an area of low pressure formed about east of Aurora. The center was north of Basco, Batanes. On the morning of July 9, JMA upgraded the system to a tropical depression. It was located northeast of Cagayan. In the afternoon, PAGASA upgraded the low-pressure area into a tropical depression and named it Goring. After making landfall on Fujian, China, it dissipated on the evening on July 10. However, the JMA classified the system as a tropical depression until the evening of July 10.

Typhoon Ma-on (Ineng)

An area of convection spawned a small area of low pressure on the morning of July 9. It became a tropical disturbance as it passed over the warm waters of the Pacific Ocean. On July 11, both the JMA and JTWC upgraded the tropical disturbance to a tropical depression which was located near Minamitorishima. On July 12, both the JMA and JTWC upgraded the system to a tropical storm and named it Ma-on. Early on July 13, the JMA upgraded Ma-on to a severe tropical storm and later that day strengthened into a typhoon. After absorbing Tokage, Ma-on reached its peak intensity on July 16. The PAGASA named it Ineng on July 17.

While Ma-on was affecting Japan, the JTWC downgraded it to a tropical storm in the evening on July 19, before making landfall on Tokushima later in the day. The JMA downgraded Ma-on to a severe tropical storm after it made landfall in Wakayama early on July 20. The JTWC downgraded Ma-on to a tropical depression on July 21, and discontinued advisories the following day. The JMA downgraded Ma-on to a tropical storm early on July 23 and transitioned into an extratropical cyclone east of the Tōhoku region the next day.

Tropical Storm Tokage (Hanna)

On July 11, the JTWC started to monitor a tropical disturbance that had developed within a poorly organized monsoon trough about to the northwest of Hagatna, Guam. Over the next couple of days, the disturbance moved towards the west and despite the system being in an area of low vertical wind shear, deep convection surrounding the system struggled to organize around the disturbances low level circulation center. However, by 06:00 UTC on July 13, it had organized enough for the JMA to declare the disturbance a tropical depression. Over the next two days, the system continued to move towards the west and gradually consolidated further. The JMA then named the system as Tokage, as it had developed into a tropical storm and reached its 10-minute peak wind speeds of . PAGASA then initiated advisories on the system and named it Hanna, before the JTWC designated the system as Tropical Depression 09W and initiated advisories on the system, while it was at its 1-minute peak wind speeds of . However, by this time Tokage was already interacting with Typhoon Ma-on, with Ma-on's outflow exposing Tokage's low level circulation center, and displacing convection to the west. The JMA, PAGASA and the JTWC then issued their final advisories on the system later that day as the remnants of Tokage was absorbed into Ma-on, due to the Fujiwhara effect late on July 15.

Severe Tropical Storm Nock-ten (Juaning)

Early on July 22, an area of low pressure formed to the east of Philippines. The system gradually drifted west over the next few days and late on July 24, the JTWC started monitoring the system as a Tropical Depression. Early the next day, the JMA upgraded the area of low pressure into a Tropical Depression. A few hours later, the PAGASA started monitoring the tropical depression and named it 'Juaning'. The system continued to drift westwards and strengthened rapidly, that on midnight, that day, the JMA further upgraded the system into a Tropical Storm, naming it Nock-Ten. Early on July 27, the JMA reported that Nock-ten continued to strengthen and upgraded it into a Severe Tropical Storm. A few hours later, the JTWC reported that Nock-ten rapidly intensified to a category 1 typhoon and made its landfall over northern Aurora (province) and started weakening. Later the same day, the JMA reported that Nock-ten has exited the Luzon island at Candon maintaining severe tropical storm strength. However, overnight, the storm rapidly weakened and the JMA downgraded it into a minor tropical storm the next day. However, on July 29, the storm gradually regained strength and approached south China coast at Qionghai, China. Later that day, the storm strengthened over land and headed north towards Hainan's provincial capital region Haikou. Over the next day, the storm drifted to the west and made landfall over Northern Vietnam. The storm weakened rapidly and at midnight that day, the JMA, issuing their final warning on the system, downgraded it into a tropical low.

The provinces of Albay

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