Tropical Storm Danas

Pre-Landfall 1 | Summary
Posting Date: October 8, 2013, 1:50:00 PM

After pounding Okinawa with the outer reaches of its 230 km/h winds Monday evening local time, Typhoon Danas has weakened to tropical storm strength and it is passing through the Korea Strait into the cooler waters of the Sea of Japan, where it is expected to weaken further.

Current Conditions

As of the Japan Meteorological Agency’s (JMA) 1700 UTC analysis today (2:00 a.m. local time), Tropical Storm Danas had maximum 10-minute sustained winds of 92 km/h with gusts up to 130 km/h. Danas’s center was located about mid-way in the Korea Strait about 240 km from the city of Hiroshima in Japan and 100 km from Busan in South Korea. Danas’s tropical storm force winds extend outward about 110 km to the northeast and 60 km to the southwest. It is currently moving to the northeast at about 35 km/h.

Tropical Storm Danas began as a tropical depression northeast of Guam on October 3 and became a tropical storm late the next day. By the time it passed just north of Okinawa on October 7, Danas had winds of 184 km/h (10-minute sustained)—a Category 4 storm on the Saffir-Simpson Hurricane Wind Scale. Typhoon Danas arrived at the island prefectures of Okinawa and Kagoshima on the heels of Typhoon Fitow, which impacted the region just three days earlier. After leaving Okinawa, Danas weakened to Category 1 status as it approached the Korea Strait, and it has since weakened further.

Exposure at Risk

Minimal structural damage from wind is expected from Tropical Storm Danas once it makes landfall in northern Honshu. In the countryside, wood frame homes dominate residential construction. Many have heavy, clay tile roofs meant to prevent damage from wind. At Danas’s forecast wind speeds, these buildings are expected to possibly have minor roof damage and little or no structural damage. Larger multi-family apartment buildings, and commercial and industrial structures, are generally engineered and made of reinforced concrete or steel, making them even less vulnerable to Danas’s winds. Modern urban structures are similarly expected to experience little or no damage.

Thus, the chief remaining impact from Danas is expected to be damage from heavy precipitation and the effects of flooding and mudslides, mostly in the relatively circumscribed northern part of Honshu—Tohoku—where Danas is now expected to make landfall. The vulnerability of buildings to flood damage varies by how they are constructed. 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 single-family buildings, and are thus better able to resist flood loads. Given Danas’s current speed of forward movement (45 km/h), however, there may be less rainfall accumulation than anticipated earlier.

Reported Impacts

At Okinawa, the two typhoons in three days, Fitow and Danas, dropped as much as 23 centimeters of rain on the island. No significant damage has been reported, however. On Yoron Island in Kagoshima Prefecture northeast of Okinawa, Danas’s strong winds shattered the town hall’s windows and damaged a wall. Throughout the region, about 30,000 homes lost power. Naha International Airport on Okinawa canceled 85 flights, while 107 domestic flights were canceled throughout southern Japan. The 100,000 barrel-a-day Nishihara oil refinery and also the Mizushima refinery on Okinawa halted their operations, and shipping to the island was also halted.

In the southern Korean peninsula, the Busan Port Authority canceled the only ferry service between Busan and Jeju Island; other ferry service was also canceled, including to cities as far away as Osaka. Danas is only the fourth “October Typhoon” to impact Korea since 1950; the last October typhoon was in 1998. As Danas approached the Korea Strait, China issued an orange alert for its nearby coastal region, the second-highest warning level for dangerous waves.

Forecast Track and Intensity

The 24^th typhoon of the current Northwest Pacific tropical cyclone season, Danas became the fourth strongest tropical cyclone to develop anywhere this year when it reached Category 4 status. Prior to Danas entering the Korea Strait, however, it began to experience shear to its north. The system also began undergoing extratropical transition. As Danas leaves the Strait it will encounter more shear and even cooler sea surface temperatures. It is forecast to become embedded within a mid-latitude trough and complete its extratropical transition in the next 24 hours.

It is then that Danas is forecast to make landfall in northern Honshu and then emerge back over the Pacific Ocean. Danas continues to produce heavy rainfall, which is the main impact expected from the storm. The AIR Tropical Cyclone Team is continuing to follow Tropical Storm Danas and will report as conditions may warrant.

Tropical Storm Danas forecast track

Pre-Landfall 1 | Downloads
Posting Date: October 8, 2013, 1:50:00 PM