Tropical Storm Talas

Pre-Landfall 2 | Summary
Posting Date: September 2, 2011, 1:45:00 PM

Current Situation Tropical Storm Talas, down from Category 1 strength yesterday, is approaching Japan today, and will make landfall on Shikoku island—the smallest and least populated of Japan’s four main islands—by roughly 21:00 UTC tonight (6am local time, September 3). Although Talas has weakened to tropical storm strength, it could still deliver heavy rainfall, though this precipitation will be heaviest (at up to 800 millimeters) in isolated, mountainous areas of Japan. As of the Japan Meteorological Agency’s (JMA) 18:40 UTC update today, Talas has maximum sustained winds of 108km/h, making it a relatively strong tropical storm. Exposure at Risk Japan has strict and well-enforced construction codes; modern structures are expected to withstand Talas’ forecast wind speeds with minimal damage, making the primary concern from Tropical Storm Talas flood damage. Flood damage in Japan is not automatically included in wind policies. In typical flood policies here, a specified payout is made only when the actual damage falls within a specified range. The vulnerability of buildings to flood damage varies by construction type. For a given flood depth, a residential wood-frame building is expected to sustain more damage than a residential masonry building. Concrete construction is less vulnerable to flood than steel or masonry. Commercial and apartment buildings usually have stronger foundations than residential buildings, and are thus better able to resist flood loads. Flood vulnerability also varies by building height. Because damage is usually limited to the lower stories of a building, high-rise buildings will experience a lower damage ratio—the ratio of the repair cost and the total replacement value of the building—than low-rise buildings because a smaller proportion of the building is affected. Reported Impacts Japan’s mountainous coast has enhanced precipitation on the north and east sides of Talas on its approach to Japan, creating moderate flood and landslide hazards. Indeed, Talas’s outer rain bands were already beginning to impact eastern and western parts of the country with precipitation yesterday (local time). On Honshu Island in the city of Shunan, in the western prefecture of Yamaguchi, rainfall of 66.5 millimeters per hour was observed Friday; this amount represents a September record for this location. The outer rain bands of Talas have also reached Hokkaido, Japan’s northernmost island; one house in Hokkaido has been flooded, according to early reports. Airlines have cancelled dozens of flights, Japan Railways has stopped some of its train service, and numerous expressways have been closed. One person surfing near the southern island of Tanegashima was missing and seven were injured in weather-related accidents in central and western Japan. According to current measurements from Tropical Rainfall Measuring Mission satellites, total accumulated precipitation of 100-200 mm is likely from Talas, while higher amounts of 400-800 mm are expected, but only in the sparsely populated mountains of Shikoku. Since Talas was and continues to be slow-moving, the JMA indicated it will likely bring moderate rainfall and tropical-storm force winds to a wide area of the archipelago of Japan. That said, because of the particular track of the storm northward across Japan (and not along the lengthy coast), the duration of strong winds and heavy rainfall will be reduced. Prior to landfall, the Joint Typhoon Warning Center (JTWC) described Talas as a “puzzling” storm. Its analysis revealed an unusual upper-level pattern with an upper low over the storm’s center and anti-cyclonic flow around the storm’s periphery. This structure has somewhat inhibited upper level outflow and deepening over the last day or so. Forecast Track and Intensity Talas is forecast to make landfall on Shikoku Island at 21:00 UTC (roughly 6am local time Saturday) and then travel north, crossing into Honshu Island several hours later. It will pass close to the cities of Kobe, Osaka, and Kyoto. After tracking northward across Japan, Talas is expected to exit into the Sea of Japan, where it will pick up speed as it interacts with an eastward-moving trough, and it will then recurve towards the northeast as it crests the subtropical ridge, currently located east of Japan. A second landfall is possible on Sunday anywhere from the Primorsky Krai region of far eastern Russia to the west coast of Hokkaido Island. Tropical Storm Talas’s track bears similarities to that of Tropical Storm Nathan, which crossed Japan in 1993, with little to no impact. Flood Hazard In the past fifty years, following several devastating flood events, the government of Japan has worked to protect the country against future flood losses. Today, large-scale flood control structures (LFCS) in Japan include dams, embankments, underground cisterns and super levees. Thus, flood risk in Japan depends on both the accumulated runoff (which is a function of precipitation level, topography, and soil conditions) and flood defenses, which vary by region. Talas, the year's 12th typhoon, is forecast to weaken after landfall. Given the relatively weak winds and moderate precipitation in populated areas, as well as the track of the storm—which will limit the duration of damaging wind and rain in Japan—AIR does not expect significant insured losses from Talas. As always, however, there remains uncertainty and the AIR Tropical Cyclone team will provide updates if warranted.

Pre-Landfall 2 | Downloads
Posting Date: September 2, 2011, 1:45:00 PM