Typhoon Tembin

Pre-Landfall 1 | Summary
Posting Date: August 23, 2012, 1:40:00 PM

Current Situation

Typhoon Tembin, the 14th typhoon 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, local time. Its path could, however, be affected by Bolaven, another typhoon around 990 miles east of Taiwan. Tembin formed on August 16 as a tropical disturbance southeast of Taiwan and was upgraded to Tropical Storm status on August 19. When it was 250 kilometers east of Taitung, Tembin had a radius gale force winds of 180 kilometers, packed winds gusting to 144 kilometers an hour, and was moving west at six kilometers per hour. Tembin is likely to make landfall with sustained winds of less than 70 knots but its slow progress and interaction with coastal mountains mean that it is likely to deliver torrential rain over southern Taiwan. Conscious of its lack of preparedness when Typhoon Morakot struck Taiwan in 2009, the government has put up to 50,000 soldiers on alert equipped with inflatable boats and amphibious vehicles to help with relief efforts in areas likely to be impacted by the typhoon. Workers were sent home in the eastern city of Hualien, where all flights were cancelled. Schools were closed in Hualien, Taitung and in parts of Kaohsiung county in the south. Farmers urgently harvested crops ahead of the storm's arrival, and windows were boarded up at many homes and businesses in eastern Taiwan to minimize damage. The authorities evacuated 3,000 residents from mountainous areas anticipating torrential rain that could cause landslides.

Flood Hazard

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 than over open water. Taiwan is a mountainous and steeply sloped country (74% of the country has elevations above 100 m, or below 100 m with slopes greater than 5%) 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.

Exposure at Risk

In Taiwan, low- to mid-rise buildings 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, 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. 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 commercial and industrial buildings in Taiwan usually date 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. About half of Taiwan’s commercial and industrial stock is made of steel while the rest is mostly reinforced concrete. Although significant wind 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.

Forecast Track and Intensity

The storm is expected to maintain intensity prior to landfall with atmospheric conditions that are generally favorable through the time of landfall with 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 even 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. The AIR tropical cyclone team is monitoring Typhoon Tembin closely and will provide updates as warranted by events.

Pre-Landfall 1 | Downloads
Posting Date: August 23, 2012, 1:40:00 PM