Typhoon Koppu (Lando) Lashing Philippines; Flooding, Mudslides Possible

Nick Wiltgen
Published: October 18,2015




 

Typhoon Koppu, known as Lando in the Philippines, is drenching the country's main northern island of Luzon and will continue to do so for several days, bringing a risk of life-threatening flash floods and mudslides.
Among the hardest-hit areas are the eastern coastal town of Baler, where significant building damage was reported Sunday morning; and the inland city of Cabanatuan, about 60 miles north of Manila, where widespread flooding was reported and several rescues requested.
Power outages were reported province wide in Pangasinan, Cagayan, Isabela, Quirino, Nueva Vizcaya, Aurora, Nueva Ecija, Apayao, and Kalinga, according to the Philippines National Disaster Risk Reduction and Management Council. At least two deaths have been blamed on Koppu and several others are missing. For the lastest news on impacts from Koppu, click the link below.
(MORE: Philippines Feeling Destructive Impacts of Typhoon Koppu)
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.

Enhanced Satellite

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.
Koppu's outer rainbands lashed parts of the Philippines Friday and Saturday while winds in its inner core continued to power up. The powerful tropical cyclone is expected to trace a painfully slow and dangerously rainy path near the northwestern coast of Luzon early this week.
As of Saturday night local time, sustained winds had reached as high as 67 mph at Baler, both on the east-central coast of Luzon. Higher winds likely occurred in the sparsely populated region hit by the eye of the typhoon.

Catastrophic Flood Threat from Days-Long Deluge

Koppu (Lando) is a particularly worrisome flood risk because it is expected to move very slowly near the northwest coast of Luzon the next few days.
Rainfall potential in a tropical cyclone is largely a function of the cyclone's forward speed, not its wind intensity.
Computer model guidance and official forecasts from the U.S. Joint Typhoon Warning Center and the Japan Meteorological Agency suggest the center of Koppu (Lando) may hover over or near Luzon through Tuesday or possibly Wednesday.
The first rainbands began wrapping into eastern parts of Luzon Friday. As of 8 a.m. Monday local time, the city of Virac, on an island just off the southeast end of mainland Luzon, had already picked up 179.4 millimeters (7.06 inches) of rainfall since the start of Friday.

Rainfall Totals

In northern Luzon, Baguio had 208.3 millimeters (8.20 inches) of rainfall as of Monday morning, with at least 2 feet of additional rain possible in the coming days.
Casiguran reported 127.0 millimeters (5.00 inches) of rainfall as of Saturday night before the station stopped reporting, possibly due to extreme winds.
With Koppu's rainbands covering Luzon and slow movement of the storm, the island could be looking at several days of heavy rainfall from Koppu/Lando before what's left of it finally drifts farther north.
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) are likely over parts of Luzon, particularly the Cordillera Autonomous Region encompassing the mountain ranges of northwestern Luzon.

Rainfall Forecast

One city particularly prone to extreme rainfall in this type of scenario is Baguio, which 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.
Astronomical as those figures may sound, forecasts from two of the world's best-performing computer models – the American GFS and the European ECMWF models – earlier predicted peak rainfall totals far exceeding 50 inches (1,270 millimeters) in the mountains lining the northwestern coast of Luzon.
Since then, the center of Koppu's circulation has moved farther west than most of the models had anticipated. In addition, despite the serious flooding in some areas, rainfall amounts observed so far have come in well below expectations for most of northern Luzon.
As a result, it does not appear that extreme rainfall totals will occur over as a large an area as earlier feared.
Still, the basic ingredients are still in place – westerly onshore winds south of Koppu's center blowing east into a north-south mountain range with a fairly steep rise in elevation. Furthermore, with Koppu's center potentially hovering offshore instead of inland, its winds may not wind down as quickly as once thought.
Therefore, there is still a threat of very heavy rainfall, leading to additional mudslides and life-threatening flooding, over parts of northern Luzon.
The government of the Philippines, which has recently undertaken considerable effort to improve its disaster management system, is actively planning ahead, anticipating the potential for serious flash flooding and mudslides.
(MORE: Filipinos Prepare for Typhoon Lando)
Some 15 to 20 million people live in the area of northern Luzon north of Manila, many of them in cities with steep hillsides or flood-prone rivers, and in some cases both.
Also worrisome is the potential for torrential rainfall in Metro Manila, one of the world's most densely populated cities with an estimated population of some 12 million people on an area of land the size of New York City minus Staten Island. Locally heavy rain could trigger dangerous flash flooding there.
(FORECASTS: Manila)

Rapid Intensification Occurred

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.

Sustained Wind Forecast

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?)

Typhoon Koppu: Track Forecast

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.
With the center of Koppu (Lando) having jumped all the way across Luzon and into the South China Sea, its winds may be a bit slower to weaken than previously thought. Locally damaging winds may persist for several days 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 significant threat, even in areas that don't see the strongest winds. Widespread power outages have already occurred.
The Philippine weather agency, PAGASA, had hoisted Storm Signal No. 4 for Aurora province and the southern half of Isabela province. There are no longer any areas under the No. 3 or No. 4 storm signals, which warn of winds exceeding 120 and 170 kph (75 and 106 kph), respectively.
As of PAGASA's 5 a.m. bulletin Monday, Storm Signal No. 2 remained in effect for much of northwestern and far northeastern Luzon, including the provinces of Benguet, Cagayan, Nueva Vizcaya, Ilocos Sur, La Union, Ilocos Norte, Abra, Pangasinan, Ifugao, Mountain Province, Kalinga and Apayao. This means winds of 61 to 120 kph (39 to 75 mph) are possible within 24 hours.
Storm Signal No. 1 for 30- to 60-kph (19- to 38-mph) winds remains hoisted for the rest of northeastern and central Luzon as well as for Metro Manila.

Future Beyond the Philippines

Typical of tropical cyclone forecasts beyond three days, uncertainty exists in the future track of Koppu (Lando) once it departs the Philippines.
Some forecast models show Koppu taking a painfully slow northward track this week, starting near or over the Philippines and continuing toward the vicinity of Taiwan, the southernmost islands of Japan.
Koppu would likely be much weaker, following its prolonged interaction with land in Luzon, but this would bring exceptionally heavy rainfall to Taiwan and, to a lesser degree, southern Japan.
High surf and storm surge would also be potential problems. However, unless Koppu spends far less time over land than currently expected, its residency over Luzon should reduce its winds to 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)
Meteorologists Jonathan Erdman, Quincy Vagell and Chris Dolce contributed to this story.
MORE: Typhoon Koppu Photos