Super Typhoon Koppu (Lando) Leaves Behind Massive Flooding in Philippines (RECAP)

Former Super Typhoon Koppu, known as Lando in the Philippines, was downgraded to a remnant area of low pressure Wednesday morning (Oct. 21) as it drifted over that country's small northernmost islands. Koppu drenched the country's main northern island of Luzon with as much as 43 inches of rain during its slow, meandering journey across the country.

Dozens of deaths were blamed on Koppu, and thousands of people were displaced.

(MORE: Filipinos Tally Destructive Impacts of Koppu)

Among the hardest-hit areas were the eastern coastal towns of Baler and Casiguran, where significant building damage was reported. Koppu made landfall in Casiguran early Sunday, Oct. 18.

Some of the most widespread flooding was reported in the province of Nueva Ecija, including the inland city of Cabanatuan, about 60 miles north of Manila. The Associated Press reported that some villagers in the province were trapped in their homes and on rooftops.

The area around Baguio City was also hit hard, as expected, by extremely heavy rainfall that caused several deadly mudslides.

Power outages were reported province-wide during the height of the storm in Pangasinan, Cagayan, Isabela, Quirino, Nueva Vizcaya, Aurora, Nueva Ecija, Apayao, and Kalinga, according to the Philippines National Disaster Risk Reduction and Management Council. The outages affected an estimated 9 million people, or nearly one-tenth of the entire population of the Philippines.

Flood, Mudslide Threat from Days-Long Deluge

Koppu (Lando) was well-anticipated as a worrisome flood risk because of its very slow movement near the northwest coast of Luzon.

Rainfall potential in a tropical cyclone is largely a function of the cyclone's forward speed, not its wind intensity, so the risk of severe flooding was anticipated well in advance.

As Koppu (Lando) meandered slowly just off the northwestern coast of Luzon, the wind circulation around it drove moisture-laden air from the South China Sea directly into the north-south mountain ranges of the Ilocos and Cordillera regions. With additional lift for the moist air provided by Luzon's mountainous terrain, rainfall totals topped 20 inches over parts of Luzon, particularly the Cordillera Autonomous Region encompassing the mountain ranges of northwestern Luzon.

The main city in the Cordillera region, Baguio, reported more than 43 inches (1,090 millimeters) of rain during the storm, of which more than 32 inches (800 mm) fell in a 24-hour period Monday and early Tuesday.

Baguio is no stranger to extreme rainfall from slow-moving tropical cyclones. It received more than 2,200 millimeters (87 inches) of rain in four days from a tropical cyclone in 1911. More recently, Typhoon Pepeng (international name Parma) dumped 73 inches of rain in seven days on Baguio in October 2009, unleashing severe flooding and mudslides that killed 465 people in other parts of northwestern Luzon.

Heavy rainfall also occurred across much of Central Luzon, an administrative region encompassing several provinces north of Manila. However, the two primary weather observation sites – Casiguran and Cabanatuan – stopped reporting data during the height of the storm. Estimates from NASA's Global Precipitation Measurement satellite indicated at least 10 inches (250 mm) of rain fell across a broad swath including those areas.

Much of that water then drained into the Cagayan River valley, leading to extensive flooding of one of the Philippines' major agricultural production regions.

The Philippine government said Wednesday that agricultural losses alone amounted to at least 6.3 billion pesos (about $135 million in U.S. currency).

Rapid Intensification Before Landfall

As Koppu (Lando) first approached the east coast of northern Luzon, favorable winds aloft spreading apart from the center of the typhoon helped it to strengthen quickly as very warm seawater fed moisture and warm air into its core of powerful thunderstorm activity.

Koppu (Lando) made landfall as a super typhoon near Casiguran in Luzon's Aurora province at 1 a.m. local time Sunday morning, Oct. 18. There was no official advisory at the exact time of landfall from the U.S. military's Joint Typhoon Warning Center, but several hours earlier JTWC had estimated Koppu's top sustained one-minute winds at 150 mph (240 kph), the equivalent of a Category 4 on the Saffir-Simpson Hurricane Wind Scale.

According to NOAA's "best track" database, only 11 Category 5 equivalent super typhoons have made landfall in Luzon since 1952. The last to do so was Megi, exactly five years ago to the day of Koppu's landfall (Oct. 18, 2010).

The Japan Meteorological Agency, which uses a different intensity scale and a 10-minute average for computing sustained wind speeds, rated Koppu (Lando) a "very strong typhoon," its second-highest category, with maximum sustained winds of 100 knots (115 mph) at the time of landfall. JMA estimated the typhoon's minimum central pressure upon landfall to be 920 millibars.

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Because it is one of the most tropical cyclone-prone coastlines on Earth, settlement along the east coast of northern Luzon is quite sparse. A large part of the coastline is virtually uninhabited, but Koppu (Lando) crossed the coast south of the most desolate zone and instead hit Aurora, a province of about 200,000 people that hugs the eastern coastline of Luzon northeast of Manila.

Meteorologists Jonathan Erdman, Quincy Vagell and Chris Dolce contributed to this story.

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