Typhoon Tembin Approaching Taiwan: AIR Analysis

August 24, 2012

According to catastrophe modeling firm AIR Worldwide, Typhoon Tembin, the 14th of the 2012 Pacific season, is “heading slowly for southern Taiwan, and is expected to make landfall in the early morning of Friday, August 24. Its path could, however, be affected by Bolaven, another typhoon around 990 miles [1584 kms] to the east.”

Tembin is “likely to make landfall with sustained winds of less than 70 knots [80.555 mph, 129 km/h], but its slow progress and interaction with coastal mountains mean that it is likely to deliver torrential rain over southern Taiwan.”

AIR said that even though “significant damage is not expected in any of the areas affected by Tembin, some occasional damage may be seen to metal roof coverings or building envelopes. Damage from flash floods or mudslides is also possible and to protect crops farmers urgently harvested ahead of the storm’s arrival.

“72-hour precipitation accumulations near the center of Tembin are as high as approximately 300 mm (TRMM). Given the typhoon’s slow movement and enhancement due to interaction with coastal mountains, higher precipitation totals are likely to occur over Taiwan. Taiwan is a mountainous and steeply sloped country (74 percent of the country has elevations above 100 meters [app. 300 feet], or below 100 meters with slopes greater than 5 percent) with some of the largest river discharges, per unit drainage area, in the world. Debris flow and landslide mitigation, combined with gully erosion control, and slope protection have been implemented to cope with these hillside zones.”

According to AIR, “low- to mid-rise buildings in Taiwan usually have reinforced concrete frames with brick infill walls. Some masonry residential buildings can also be found, although these are usually built prior to 1950 and are often designed in the Japanese style. In recent years, these residences have given way to mid-rise apartment buildings and three-story street houses (tow tien), with both types generally of masonry construction. Most of the buildings in Taiwan are fairly new however and recent residences tend to be high-rise complexes built in clusters. These are predominantly reinforced concrete, many with ceramic facades, although some are steel (Su, 2002). Taiwan’s residential buildings usually have commercial establishments on the first floor, while the upper stories are used for residential purposes. The mixed occupancy use in Taiwan makes the vulnerability of residential and commercial lines of business very similar.”

The analysis described commercial and industrial buildings in Taiwan as usually dating “to 1970 or later, since before that time the country relied more heavily on agriculture. These buildings are therefore generally built to better structural standards (Su, 2002). About half of Taiwan’s commercial and industrial stock is made of steel while the rest is mostly reinforced concrete. As described above, the vulnerability of Taiwan’s commercial and industrial buildings is similar to residential, due to the prevalence of mixed-occupancy buildings.”

AIR added that it expects the storm “to maintain intensity prior to landfall with atmospheric conditions that are generally favorable through the time of landfall (low shear and warm sea surface temperatures). The only factor detrimental to intensification is interaction with Taiwan. Short-term fluctuations in the intensity of strong typhoons due to internal processes are always possible and hard to predict, and it is possible that Tembin could increase in intensity prior to landfall, although any such growth is likely to be modest.

“Tembin is expected to weaken as it passes over Taiwan, on a west-southwest track. After reemerging over water, steering winds are weak and the storm may turn back towards Taiwan.”

Source: AIR Worldwide

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