Remnants of Koppu (Lando) Drenching the Philippines; Flooding, Mudslides Possible

Nick Wiltgen
Published: October 20,2015



 

The ex-tropical storm Koppu, known as Lando in the Philippines, has drenched the country's main northern island of Luzon with locally more than 40 inches of rain since this past weekend. Although what's left of the system is moving slowly away from the northern Philippines, additional heavy rain is possible through Wednesday, which could contribute to more flooding.
Several deaths have been blamed on Koppu and thousands of others have been displaced. For the latest news on impacts from Koppu, click the link below.
(MORE: Philippines Feeling Destructive Impacts of Koppu)
Among the hardest-hit areas are the eastern coastal towns of Baler and Casiguran, where significant building damage has been reported. Some of the most widespread flooding has been 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.
Power outages were reported province wide this weekend in Pangasinan, Cagayan, Isabela, Quirino, Nueva Vizcaya, Aurora, Nueva Ecija, Apayao, and Kalinga, according to the Philippines National Disaster Risk Reduction and Management Council.

Enhanced Satellite

Flood, Mudslide Threat from Days-Long Deluge

Koppu (Lando) has been a particularly worrisome flood risk because of its very slow movement near the northwest coast of Luzon the last few days.
Rainfall potential in a tropical cyclone is largely a function of the cyclone's forward speed, not its wind intensity.

Rainfall Totals

In northwestern Luzon, Baguio had 1077.8 millimeters (42.43 inches) of rainfall as of Wednesday morning, with a couple inches of additional rain possible through Wednesday.
Therefore, we could still see additional mudslides and life-threatening flooding over parts of northwestern Luzon.
Rainbands in tropical cyclones can easily produce more than 2 inches of rain per hour. With additional lift for the moist air provided by Luzon's mountainous terrain, extreme storm totals of 20 to 40 inches (500 to 1,000 millimeters) have fallen over parts of Luzon, particularly the Cordillera Autonomous Region encompassing the mountain ranges of northwestern Luzon.

Rainfall Forecast

The aforementioned city of Baguio is very prone to extreme rainfall in this type of scenario. 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.
In August 2015, Typhoon Goni brought more than 28 inches (700 mm) of rain to Baguio and nearby parts of northwestern Luzon in three days, even though it never made landfall in the country. The rain unleashed flash floods and mudslides that accounted for most of the storm's death toll of 33 in the Philippines.
Locally damaging winds may persist for the next day or so thanks to the system's slow movement. The strongest winds will tend to be near the coast.
Given moist soil from the torrential rain, falling trees will continue to be a threat, even in areas that don't see the strongest winds.
(FORECASTS: Manila)

Future Beyond the Philippines

Koppu will track slowly northward through this week, starting near the northern Philippines and continuing toward the vicinity of Taiwan and the southernmost islands of Japan.

Koppu: Track Forecast

Koppu is forecast to remain weak, due to its prolonged interaction with land in Luzon. However, we could see heavy rainfall in Taiwan and Japan's Ryukyu Islands
Winds should be at levels well below those required to cause significant damage in Taiwan and southern Japan, where most of the infrastructure is built to withstand extremely strong typhoons.
(FORECASTS: Taipei)

Rapid Intensification Occurred This Weekend

Favorable winds aloft, spreading apart from the center of the typhoon, helped the super typhoon strengthen as very warm seawater fed moisture and warm air into its core of powerful thunderstorm activity.
Koppu (Lando) may have attained Category 5 equivalent status prior to landfall, but there was no official advisory at the time of landfall from the Joint Typhoon Warning Center.
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.
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).
(WATCH: What Does the Cone of Uncertainty Mean?)
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.

Koppu's Landfall

Koppu (Lando) made landfall as a super typhoon near Casiguran in Luzon's Aurora province at 1 a.m. local time Sunday morning after a long-feared rapid intensification. The U.S. military's Joint Typhoon Warning Center estimated its top sustained one-minute winds at 150 mph (240 kph) before landfall, the equivalent of a Category 4 on the Saffir-Simpson Hurricane Wind Scale.
Based on JTWC data, Koppu (Lando) is the strongest landfalling tropical cyclone on Luzon in five years. The most ominous threat for the Philippines, however, should be its prolific rainfall as it grinds across the mountains and valleys of Luzon, the main island of the northern Philippines and home to almost half of the country's 98 million people.
Meteorologists Jonathan Erdman, Quincy Vagell and Chris Dolce contributed to this story.