Storm surge: Biggest threat from tropical cyclone (SunStar)

(UPDATED) Typhoon Yolanda (international name: Haiyan) has just demonstrated how big waves generated by strong winds can engulf communities similar to a tsunami whenever there is a major earthquake.

Tacloban City, for one, was devastated as waves as high as 20 feet upturned cars and drowned animals and people who failed to escape the rampaging waters. Local officials say the death toll in Leyte alone can reach 10,000.

Until now, the Philippine Atmospheric Geophysical and Astronomical and Services Administration (Pagasa) still does not have an official figure on the height of the storm surge that hit the city last Friday.

“But based on eyewitness accounts, it’s fair to say that storm surge was the reason behind the high death toll there,” said weather forecaster Jori Loiz.

No warning?

The disaster did not come without warning. Pagasa had said Yolanda, packing sustained winds of 235 kilometers per hour (kph) with gusts of 275 kph when it touched land, can generate maritime surges of up to seven meters or 23 feet.

The Department of Science and Technology’s Project NOAH (Nationwide Operational Assessment of Hazards), meanwhile, forecast a wave height of 4.5 meters in Tacloban, 3.8 meters in Ormoc City (also in Leyte) and 5.3 meters in Matarinao Bay in Eastern Samar, where Yolanda first made landfall.

Even the Manila Observatory, an independent research institution based in Quezon City, wrote in its technical report on November 7, prior to Yolanda’s landfall, that the typhoon could bring a lot of rainfall which could cause flashfloods, inundated low-lying areas, as well as storm surges and swells in the coastal areas.

How do storm surges occur?

Storm surges happen when the weather disturbance produces a rise of water way above the predicted astronomical tide, according to the United States National Weather Service.

As an archipelago, the Philippines is vulnerable to storm surges but the effect is dependent on several factors such as the storm’s pressure, size, intensity, forward speed and angle of approach to coast, shape of coastline, width and slope of the continental shelf and local features.

Other countries like the United States also had horrifying experiences from storm surges. In 2008, Hurricane Ike generated 15 to 20-feet storm surge, bringing extensive damage to parts of Texas. Three years prior, the infamous Hurricane Katrina dumped 28-feet high water in Louisiana.

Katrina left 1,500 people dead.

Other disasters in Leyte

Tacloban, a city of 200,000, has an elevation of around three meters, making it a shoo-in victim of abnormal water height. Footage shown by television networks also suggests that structures and houses in the city were not disaster-proof, thus, storm surges were too much to bear.

The Manila Observatory wrote in its technical report prior on November 7 that Eastern Visayas region had already been affected by severe disasters in the past.

Tropical Storm Uring (Thelma) that ravaged Ormoc City, Leyte in November 1991 and the mudslides in Guinsaugon, Southern Leyte on February 2006 claimed a total of 6,300 lives, the Manila Observatory said.

The two weeks of torrential rain in 2006 loosened the soil, which caused an entire side of the mountain to slide down and buried a large swath of the area, it said.

The location and the kind of land — mountainous with a narrow coastal plain where most of the population is concentrated — heightened the hazards in the area, the Manila Observatory said in its report.

“Landforms on the island of Leyte are characterized to be highly sheered, fractured and unstable,” it added.

Weather education

Project NOAH chief Dr. Mahar Lagmay told Sun.Star that Pagasa was able to forecast Typhoon Yolanda accurately, including the possible storm surges.

“They predicted the length and amount of wind the rainfall including the hazards, landslides, pati ‘yung storm surge height and amount of rain were also predicted,” said Lagmay.

He also said that while it is important to get the forecast right, it is up to the public to be able to understand the significance of the forecast.

“Kailangan i-inform din ang tao where to go. Dapat may educational campaign sa mga ganitong klaseng calamity… It should start from the people though; it is not Pagasa’s duty (alone). Dapat alam na ng tao kung pano i-handle ang mga concerns nila,” he said.

He also said that proper communication of weather information is vital to minimize disasters, “Communication is very important. Make the people understand that it’s not just science. (We need to make the public understand) how to digest those information.” (with reports from Third Anne Peralta/SFP/Sunnex)

This article was originally published in on November 11, 2013

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