Super Typhoon Yolanda: The recipe of a perfect tropical cyclone (Sunstar-Manila)

Monday, November 18, 2013

THE super typhoon that caused mass devastation across large parts of the Philippines was a “perfect tropical cyclone” that broke many world records, said meteorologists from around the world.

The death toll from Super Typhoon Yolanda (Haiyan) continued to rise nine days after it wreaked havoc in the Visayan region. As of November 17, the official count was at 3,976, with 1,590 still missing.


The Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa) said that at its peak, Yolanda’s wind speed was around 255 kilometers per hour (kph). But the US Navy’s Joint Typhoon Warning Center’s forecast was even higher at 315 kph, about the speed of a single-propeller aircraft.

The state weather bureau Pagasa raised Public Storm Warning Signal Number 4 over several areas, a rare occurrence when cyclones struck the Philippines. Yolanda is also Category 5 in Saffir-Simpsons Hurricane Scale, capable of causing “catastrophic damage.”

Yolanda’s diameter, at 600 kilometers (km), was a record-holder. Satellite images during Yolanda’s wrath showed that the super typhoon covered the entire Philippine archipelago, bringing rain to most parts of the country.

Perfect condition = recipe for disaster

Dr. Gerry Bagtasa of the University of the Philippines Institute of Environmental Science and Meteorology said the conditions were perfect to turn Typhoon Yolanda into a massive cyclone.

Cyclones form if a combination of several factors, including low atmospheric pressure, higher sea surface temperature and high moisture content, are satisfied.

Cyclones are huge rotating wind systems with low atmospheric pressure. They produce cloudy weather and bring rain or snow. (In the United States, they are called hurricanes while in the Philippines, they are tropical cyclones – tropical depression to super typhoons, depending on wind speed). Their intensities are measured according to their forecast wind speed.

“[There was] nothing to stop Yolanda to intensifying. It never hit a mountainous area to break its wind speed. Everything fell into place,” said Bagtasa.

He added Yolanda formed a bit farther from the Philippines so it had time to accelerate.

“Before it even entered the Philippine Area of Responsibility (PAR), it’s already a typhoon,” said Bagtasa.

But it wasn’t just Yolanda’s violent winds and massive diameter that caused disaster; the typhoon killed thousands of people and left millions in Eastern Visayas homeless because it generated storm surges.

Storm surge

But what exactly are storm surges? (See related story.)

A storm surge is an abnormal rise of water during a cyclone. The Storm Surge unit of the Department of Science and Technology’s Project NOAH (Nationwide Operational Assessment of Hazards), a two-month old unit, has been educating people about the hazard involved in storm surges.

Project NOAH’s Engineer John Phillip Lapidez told Sun.Star in an interview, “Storm surge is the rising of water during a storm, aside from the tide (caused by the gravitational pull of the sun or moon).”

If the storm surge hits the coastal area during high tide, it is more dangerous, said Lapidez.

Storm surge plus tide level is called storm tide, he added.

But there are at least four factors that affect how huge the impact of a storm surge will be, including the storm’s wind speed and intensity.

Lapidez said, “The stronger the wind, the stronger the surge.”

Yolanda, Lapidez said, is this year’s strongest cyclone in the world.

Another factor is the ocean’s depth with respect to the sea level, and the slope of the coastline.

“If the coast is gently sloping, then it is more prone to storm surges,” Lapidez explained. (See animation.)

Tacloban City in Leyte, one of the worst hit by Yolanda, has a gently sloping coast, said Lapidez.

Lapidez also said that Pagasa as well as Project NOAH forecast that the height of the storm surge to hit Eastern Visayas could reach even five meters – about two storeys high.

He also said, for as long as the storm is still within the area, the waves could continuously hit the coastal area.

Lapidez said, “We (Project NOAH) had given data and forecast to the National Disaster Risk Reduction and Management Council (NDRRMC), even if the term ‘storm surge’ may be unfamiliar, we made it clear that these areas should expect water to rise up to five meters. Whatever you call it, it’s still high.”

Meanwhile, Bagtasa added that five meters worth of seawater could cause disaster due to its volume alone.

“Each liter of water weighs approximately one kilogram. Imagine carrying five gallons of water. It’s heavy. Then imagine a huge wave thousands or even millions of gallons coming to the coast. Even if it doesn’t move fast, once it hits a wall, the wall will surely break,” Bagtasa explained.

The Philippines, an archipelago, is prone to storm surges. But not all coastal areas are vulnerable to storm surges, clarified Lapidez.

Cyclones entering PAR start from the eastern part of the country and head toward the west. Those areas that are in the path of the cyclones are considered more vulnerable than the other coastal areas, said Lapidez.

Why were Samar and Leyte the worst-hit?

The Manila Observatory, an independent research organization, wrote a paper prior to Yolanda’s landfall to assess the disaster risk of areas expected to be hit by Yolanda based on hazard, exposure and vulnerability. The hazards posed by Super Typhoon Yolanda include storm surge, landslides and floods. Exposure was measured through population density. Vulnerability, the Manila Observatory said, was measured through each province’s poverty incidence.

“Leyte and Samar were the provinces at high risk to Yolanda firstly due to their location, since these provinces were directly hit by the typhoon and thus experienced the intense winds. The very strong winds and the direction of the winds together with other factors… led to the high storm surges that these areas experienced. Unfortunately, there were no mountains on the path before it made landfall, which could have reduced the wind speeds when it reached these areas,” the Manila Observatory said.

The research institution also said that some parts of Southern Samar, which were in the direct track of Yolanda, have poverty incidence of at least 40 percent, making the population more vulnerable to disasters.

According to their assessment, Leyte also has a relatively high vulnerability to disasters, noting that its poverty incidence is between 30 and 40 percent.

“They have large populations living in urban centers located in low elevation coastal zones. This means that their lifeline services and transport (air, land sea) infrastructure are concentrated and located to serve primarily these areas,” the Manila Observatory said.

It added, “If local government is immobilized by the impact of the hazards, the breakdown in these flows becomes even more severe. In urban areas, where population density is high and inequality of incomes may be present, civil unrest is possible. Moreover, people in the peri-urban areas tend to flock to the main or capital city, or, where they believe they can get assistance, medicine, food and water.”

Bracing for disasters

Disasters occur when hazards impact vulnerable people, according to the International Federation of the Red Cross. The Project NOAH’s head, Dr. Mahar Lagmay, has always believed that while hazards cannot be taken away, disasters can be minimized.

Bagtasa said there have been studies proving that the ocean’s temperature continue to rise over past decades.

“There are still no concrete proofs the link between cyclones intensity with global warming,” said Bagtasa.

But there is a link between higher sea level, rising ocean temperature and global warming, he said.

Bagtasa also said that most of the cyclones with greater intensities were attributed to better forecasting and better technology to measure the strength of cyclones.

“Satellite images now have higher resolutions, we have better forecasting equipment than ten years ago which makes measurements more accurate,” said Bagtasa.

“It is possible that we may have experienced storms with Yolanda’s intensity in the past, we just didn’t have enough records to tell,” Bagtasa said.

The Manila Observatory told Sun.Star, “We note that in recent years that the sea surface temperatures have been higher than normal. This fuels the strength of the tropical cyclones when these travel the seas before they hit land.”

It also said, “(T)here were 15 typhoons which crossed the Visayas – Mindanao area with intensities of greater than or equal to 240 kph since the 1950s or in the last 60 years. Of these 15, four happened in the 1990s to the present.”

“The lack of coping capacity of local government and the general population in the immediate period following of a disaster of this magnitude is a major dimension of vulnerability which should be addressed in the future. Land use planning, services and infrastructure design should be integrated with vulnerability and risk reduction. Low elevation coastal areas need clear and specific risk reduction intervention programs,” the Manila Observatory said.

It added, “The Philippines has over 10 million people living in LECZs and most are in the metropolitan areas or fast growing cities. Information also needs to be shared among the different agencies to devise a more comprehensive plan of action before and after the disaster.” (Sunnex)

This article was originally published in Sunstar Manila on November 13, 2013.

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