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Typhoon Ketsana

Pacific typhoon in 2009

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Typhoon Ketsana.
NASA · Public domain

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The sixteenth tropical storm and eighth typhoon of the season, Ketsana formed early about 860 km (530 mi) northwest of Palau on September 23, 2009. Initially, it was downgraded to a low pressure area by the Japan Meteorological Agency (JMA), but after drifting through favorable conditions, it intensified the next day and was categorized as a tropical depression by the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA), and was given the name Ondoy after entering the Philippine Area of Responsibility. The Joint Typhoon Warning Center (JTWC) issued a Tropical Cyclone Formation Alert on the depression. It was then upgraded to a tropical depression by the JMA later that morning before the JTWC followed suit early on September 25, designating the depression as 17W. Soon, the depression strengthened into a tropical storm, and was given the name Ketsana by the JMA. Shortly after, it made landfall over the Philippines, and as it moved into the South China Sea, the storm intensified while moving towards the west. It peaked as a Category 2-equivalent typhoon before ultimately making landfall on Vietnam at peak intensity on September 29, dissipating on the next day.

While Ketsana made landfall north of Metro Manila as a tropical storm, it enhanced the southwest monsoon, bringing record-breaking rainfall and flooding across the Philippines' capital. At least 464 deaths and $237 million (₱11.1 billion) were attributed to the typhoon, making it the most devastating tropical cyclone to hit Metro Manila, surpassing Typhoon Patsy (Yoling) in 1970. Flood water levels also reached a record 20 feet (6.1 m) in rural areas. In response to this, President Gloria Macapagal Arroyo declared a "state of calamity" encompassing most of Luzon after at least 86 people were initially reported dead in landslides and other incidents. Recovery efforts from the storm's onslaught would later be hampered by Typhoon Parma, which made landfall in the Philippines roughly a week after Ketsana.

Meteorological history

On September 23, 2009, the Japan Meteorological Agency (JMA), reported that a seasonal tropical depression had formed about 860 km (530 mi) to the northwest of Palau. The Joint Typhoon Warning Center (JTWC) then reported later that day that the depression had a developing low-level circulation center and was in a favorable environment with low vertical wind shear. The JMA then reported that the depression had weakened into an area of low pressure. However, early the next day, as deep convection started to consolidate around the low-level circulation center, the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) reported that the low-pressure area had become a tropical depression and assigned it a local name of Ondoy. Later that morning, the JTWC issued a Tropical Cyclone Formation Alert as central convection had continued to organize around a consolidating elongated but exposed low-level circulation center. The JMA then re-upgraded Ondoy to a tropical depression later that morning before the JTWC followed suit early on September 25, designating it as Tropical Depression 17W when it was located about 400 nm east of Manila in the Philippines. At this stage, the system was moving along the southern side of the subtropical ridge and had good poleward outflow into a tropical upper tropospheric trough (TUTT) cell.

Throughout September 25 the intensification of Ondoy was hampered by the system moving into an area of moderate vertical wind shear and by an upper-level trough of pressure that was moving over the system. But later that day the JTWC upgraded it to a tropical storm despite its low level circulation center being partially exposed. The JMA followed suit early the next day, assigning the international name of Ketsana and the international designation of 0916 to the storm. PAGASA then reported that Ketsana had made landfall on Northern Luzon near the boundary of the Philippine provinces of Aurora and Quezon. As a result of making landfall, its low-level circulation center had become fully exposed, but as the storm moved into the South China Sea, it dramatically deepened and expanded while moving west and was upgraded to a severe tropical storm by the JMA early on September 27.

During September 27, Ketsana gradually developed further and was upgraded to a typhoon by the JTWC and the JMA early the next day, as multiple convective bands were continuing to consolidate more tightly around the low-level circulation center, leading to the formation of a disorganized eye. Typhoon Ketsena then intensified quickly under favorable conditions, reaching peak windspeeds later that day of 165 km/h (103 mph) (1-min winds) and 140 km/h (87 mph) (10-min winds) which made it a Category 2 typhoon on the Saffir–Simpson scale. Ketsana then made a second landfall on Quảng Nam in Vietnam, at 0600 UTC on September 29 at its peak intensity. It then rapidly weakened into a Severe Tropical Storm, with the JTWC issuing its last advisory later that day; however, the JMA continued to monitor Ketsana as a Severe Tropical Storm until later that day, when it downgraded it to a Tropical Storm before further downgrading it to a Tropical Depression early the next day when the center of the depression was located over Laos. The JMA monitored the storm as a weak tropical depression until late on September 30, when it released its final advisory.

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