Typhoon Soudelor 2015

Pre-Landfall 2 | Summary
Posting Date: August 7, 2015, 1:15:00 PM

Meteorological Summary and Forecast
Soudelor has been unable to re-attain its lifetime peak intensity, which was achieved on August 4, when the JMA estimated the typhoon’s minimum central pressure as 900 mb and maximum 10-minute sustained wind speeds of 212 km/h (233 km/h 1-minute sustained). Since that time, Soudelor has passed over a patch of ocean with relatively low oceanic heat content (OHC) as indicated by the red oval in Figure 2. OHC is a measure of the total integrated heat energy in the upper ocean, and it is a more comprehensive metric than sea surface temperature (SST) for gauging the energy available to a tropical cyclone. Atmospheric and oceanic conditions appear favorable for some intensification prior to landfall in Taiwan, as wind shear remains low and Soudelor recently passed over a warm ocean eddy with locally high OHC. Nonetheless, Soudelor is a large tropical cyclone, which tends to reduce the likelihood for rapid intensification, and possible entrainment of dry air into the storm core on the western side may also inhibit re-intensification. The JMA forecast indicates that Soudelor will maintain its present intensity through landfall, after which rapid weakening will commence.

Soudelor is expected to produce very heavy rainfall on Taiwan as the system interacts with mountainous terrain. Model forecasts from the Global Forecast System indicate widespread rainfall amounts of greater than 250 mm will occur. Impressive rainfall totals are already being observed as Soudelor’s outer bands have begun to impact Taiwan (Figure 3); as of 01:36 Taiwan Standard Time (TST) on August 8, 17 stations are reporting rainfall totals of more than 200 mm with 4 stations reporting more than 300 mm. Fortunately, Soudelor is not a slow-moving system, reducing the potential for extreme rainfall totals like those of Typhoon Morakot in 2009. Taipei, the capital of Taiwan and its largest city, will likely miss the strongest winds associated with Soudelor, but heavy rainfall and flooding is still a threat. The typhoon’s heavy rainfalls could also trigger landslides on the steep, mountainous terrain of eastern Taiwan. Finally, storm surge is a threat on the right (north) side of the storm track, particularly to areas where the terrain is relatively flat, such as Yilan County.

Soudelor is forecast to weaken rapidly after landfall in Taiwan due to interaction with the island’s high terrain, eventually making a second landfall over the mountainous province of Fujian in China.

Exposure at Risk
While not directly in Soudelor’s anticipated track, the northeast of the country, where the capital Taipei is located, is likely to be most affected because of the relatively high concentration of exposures there. Any deviation of the storm from its forecast track to the north will result in more serious impacts for Taipei, while deviation to the south would tend to lessen the impact to exposures in Taiwan.

At the estimated wind speeds of Typhoon Soudelor, Taiwan’s building stock is expected to fare reasonably well, with limited instances of significant structural damage. Storm surge may affect coastal communities while inland flooding is expected to cause significant damage to some low-rise structures, and minor roof and wall cladding damage from wind is likely. However, landslides could cause considerable damage, as they did in 2009 when Typhoon Morakot’s extreme rainfalls caused landslides that devastated the village of Xiaolin. Nearly 450 people were killed, buildings were destroyed, roads were buried, and other infrastructure, such as bridges, were compromised.

The low- to mid-rise buildings of Taiwan typically have reinforced concrete frames with brick infill walls. Some masonry residential buildings can also be found, although these are usually built prior to 1950. 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 façades, although some are steel.

Taiwan’s residential buildings usually have commercial establishments on the ground 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 only date back to 1970 or later because 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.

Pre-Landfall 2 | Downloads
Posting Date: August 7, 2015, 1:15:00 PM