Typhoon Pedring

Typhoon Nesat, known in the Philippines as Typhoon Pedring, was the most powerful tropical cyclone to directly impact China since 2005. It also struck the Philippines during the 2011 Pacific typhoon season, killing 98 people. It is the 17th named storm, the 11th severe tropical storm, the 7th typhoon and overall, the 30th tropical cyclone to be monitored by the Japan Meteorological Agency(JMA) during the year. Nesat came exactly two years after Typhoon Ketsana made landfall in the Philippines as the most devastating typhoon in the 2009 Pacific typhoon season with a damage of 1.09 billion and 747 fatalities. Nesat was also the first of twin tropical cyclones to batter the Philippines within one week during September 2011, the second was Nalgae.

The low pressure area that was to become Nesat developed on the evening of September 21, to the east-southeast of Palau. The Joint Typhoon Warning Center (JTWC) originally anticipated Nesat would become a Category 4 super typhoon on the Saffir–Simpson Hurricane Scale (SSHS) with winds exceeding (1-min sustained). However, because of a cold anomaly, the system only reached a maximum 1-min sustained wind speed of making it a powerful Category 4 typhoon. Nesat made landfall over the Luzon region of the Philippines and the maximum sustained winds dropped to . The system continued to weaken with convective banding loosely wrapped into the partially exposed low-level circulation center(LLCC). The winds continued to drop and eventually reached (1-min sustained) which made it a minimal typhoon on the SSHS. On September 29, by the time Nesat managed to re-develop a ragged eye, it made landfall over Wenchang in Hainan, China and started weakening again. Due to the rapid weakening, the JTWC ceased advisories on the storm, soon afterwards. Later that evening, the JMA downgraded Nesat to a tropical low over land and issued their final warning on the system.

As Nesat neared the Philippines, the local government ordered the evacuation of residents living in low-lying areas, cancelled flights and suspended classes on all levels. Several provinces were placed under Signal Number 2 and 1. China's flood control authority activated their emergency response system so that they can cope up with the upcoming typhoons Nesat, and Nalgae. The authority requested local governments in relevant areas to closely monitor both the typhoons and keep the public aware of what is happening. They initiated a level IV typhoon response program and sent two working teams to the provinces of Guangdong and Hainan so that they can assist people in all the preparations that they have to make. Ships were recalled, flight and ferry services were suspended and schools were shut as the strongest typhoon to directly impact Hainan in 2011 was approaching its final landfall. Macao's public transportation system was also suspended after typhoon signal No. 8 was hoisted by most local meteorological authorities. In Hong Kong, many functions and activities were canceled or postponed because of the fast approaching storm.

Early on September 27, Typhoon Nesat struck the Philippines with a maximum 1-min sustained wind speed of and killed four people after pinning them under a collapsed wall in Valenzuela. The residents of Manila had no other choice but to wade through waist-deep floodwaters, dodging branches and flying debris as the typhoon sent surging waves as tall as palm trees over seawalls, completely submerging neighborhoods. The typhoon made landfall before dawn triggering instant response. Officials in Albay province said that "About 112,000 people were ordered to leave their homes in five towns prone to flashfloods and landslides in central Albay province. Among the hardest hit provinces were Isabela and Aurora where most of the population was directly dependent on agriculture. Very similar to what happened after Typhoon Ketsana, a state of calamity was declared in Luzon in order to undertake an emergency procedure in order to ensure safe and timely water releases from the dams. Nesat approached China just one day after the preparations for it started. Because of the low strength of the storm, the damages from Nesat to China were expected to be near US$50 million. The typhoon then hit Vietnam and weakened into a tropical storm.

Meteorological history

During September 21, the Joint Typhoon Warning Center (JTWC) reported that a tropical disturbance had developed at the eastern end of a monsoon trough, about to the southeast of Melekeok on the island of Palau. The disturbance had a well defined low level circulation centre with convection flaring around it and was located in a region of moderate vertical windshear. Over the next 24 hours the depression moved towards the northeast, while gradually developing further. The Japan Meteorological Agency and the JTWC then reported during September 23 that the disturbance had developed into a tropical depression, with the latter designating it as Tropical Depression 20W.

Early on September 24, the JMA further upgraded 20W to a tropical storm and named it Nesat. Nesat continued to drift west with expanding deep convection around the entire system and consolidating convection around the LLCC. The mid-level warm anomaly near the system continued to intensify and convective banding near the LLCC became more and more tighter. As a result, the JMA upgraded Nesat to a severe tropical storm on September 25. Nesat was originally expected to have undergone rapid intensification until September 25, but the JTWC later reported that the sea surface temperatures was a little less than expected and Nesat could not strengthen rapidly. However, Nesat was still strengthening. With an extremely well developed equatoward outflow, Nesat already had a windspeed of (1-min sustained). Late on September 25, the JMA further upgraded Nesat to a typhoon.

On September 26, an image from Advanced Microwave Sounding Unit (AMSU), a multi-channel microwave radiometer installed on meteorological satellites depicted that Nesat developed an eye like feature approximately east-northeast of Manila, Philippines. At that time, it had a 1-min sustained wind speed of with deep convection primarily over the western semicircle of the system. The system rapidly deepened and quickly developed a ragged eye and mesoscale anticyclone aloft generating an exceptionally excellent all-around outflow. Also, the system had a highly symmetric radial outflow. The JTWC Originally anticipated Nesat to become a Category 5 super typhoon on the SSHS with winds exceeding (1-min sustained). However, because of a cold anomaly, the system only reached a maximum 1-min sustained wind speed of making it a minimum Category 4 typhoon.

Early on September 27, Nesat made landfall over the Luzon region of Philippines. As a result, the eyewall got eroded and the maximum 1-min sustained winds dropped to . The system approached land at nearly . However, later on that day, the LLCC started to get re-consolidated with convection as Nesat quickly moved west and re-emerged over water. At that time, it was located near the southern periphery of a deep layered subtropical steering ridge and moved towards the southwest and the winds further dropped to because of land interaction. Though the system has maintained overall central deep convection, subsidence persisted along the northwest quadrant which caused further drop in wind speed. Upper level analysis indicated that Nesat was to the south of a ridge axis in an area of moderate vertical wind shear. The system continued to weaken with convective banding loosely wrapped into the partially exposed LLCC. The winds continued to drop and eventually reached (1-min sustained) which made it a minimal typhoon on the SSHS. Though the weakening, Water vapour imagery showed that the typhoon was still maintaining excellent outflow towards the equator and improving outflow towards the pole. Nesat maintained a relatively large area of gale-force winds. Animated infrared satellite imagery depicted that the storm was expanding in size and convective banding continued to move further and further away from the LLCC. The LLCC was also relatively large, elongated and cloud free.

On September 29, by the time Nesat managed to re-develop a ragged eye, it made landfall over Wenchang in Hainan, China and started weakening again. Because of the poor shape and disorganization at the LLCC, the typhoon could only maintain a maximum 1-min sustained windspeed of . Even after the landfall, Nesat maintained vigorous convection all around the LLCC and did not weaken too much when compared to the reactions after the Philippine landfall. There was a sea-surface temperature of approximately and a slight vertical wind shear of near the system's center at that time. The JTWC anticipated the storm to gradually drift over the Gulf of Tonkin and make landfall over Vietnam with a 1-min sustained wind speed of at least . Early on September 30, Nesat made its final landfall over northern Vietnam with a 1-mim sustained windspeed of and a well-defined, tightly wrapped LLCC, and soon it started weakening. Due to land interaction, the convection around the system started decaying rapidly. Due to the rapid weakening, the JTWC ceased advisories on the storm, soon afterwards. Later that evening, the JMA downgraded Nesat to a tropical low over land and issued their final warning on the system.

Preparations and impact

Philippines

As Nesat neared the Philippines, the Philippine government ordered the evacuation of residents living in low-lying areas, cancelled flights and suspended classes on all levels. By the morning of September 26, some 111,000 people in the flood-prone areas of the Albay Province

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