Typhoon Sanba

Pre-Landfall 1 | Summary
Posting Date: September 17, 2012, 6:15:00 AM

Typhoon Sanba, which formed as a tropical depression in the western Pacific on September 10, strengthened rapidly (central pressure dropped from 975 mb to 915 mb in 12 hours) on Friday to become the strongest tropical cyclone yet of 2012. Sanba maintained super typhoon status for several hours on its approach to the Japanese island of Okinawa, packing sustained winds of 233 km/h (145 mph), gusts of near 320 km/h (200 mph), and a central pressure that bottomed out at 900 mb as it bypassed the northern Philippines well to the east. Sanba was the most intense typhoon since 2010’s Super Typhoon Megi, which had a central pressure of 885 mb. Fortunately, super typhoons (or Category 5 hurricanes) tend to be short lived. Late Friday, Sanba began an eyewall replacement cycle and by Saturday, the storm was encountering increased vertical wind shear. By the time Sanba crossed Okinawa, on Sunday morning local time, winds had dropped to 194 km/h (120mph). Sanba’s forecast track toward South Korea has remained remarkably stable. However, the storm is entering cooler ocean temperatures and has already weakened and now has 10-minute sustained winds of near 162 km/h (100 mph). Further weakening is expected and Sanba is likely to make landfall along the south central coast of South Korea near Kosong—about 70 km west of Busan—around 10:00 a.m. local time Monday at Category 2 strength (hurricane equivalent). Note, however, that there remains considerable uncertainty in both the forecast track and intensity for Typhoon Sanba. According to the Japan Meterological Agency at 12:45 a.m. UTC, Typhoon Sanba is currently traveling north at 35 km/h (22 mph). The eye of the storm is smaller than it was at its peak, but it has also become less clearly defined. Sanba has also become less symmetrical as it encounters strong westerlies. Vertical wind shear is now 20-30 knots, and should become even stronger as the system embeds into the subtropical jet stream. Precipitation from Sanba is already affecting the southern coast of South Korea. The total precipitation amounts from the storm are expected to be 200 mm in low-lying coastal regions but higher in the mountains by perhaps a factor of two. The rapid forward speed of Sanba and continued acceleration will help keep accumulations down. Sanba will begin weakening rapidly after landfall and begin undergoing extratropical transition as it accelerates northeastward across northern Korea. China's meteorological authority has warned of stormy conditions and up to 120 mm of rain in parts of Heilongjiang and Jilin provinces. Sanba is not currently expected to make landfall across any of the main islands of Japan.

Reported and Expected Damage

This was the second time in less than three weeks that Okinawa has had to deal with typhoon conditions. On August 26, a Category 3 Typhoon Bolaven crossed the island, but caused little damage to Okinawa's predominantly concrete building stock, which is well prepared to handle storms of this intensity. Although damage assessments from Sanba have just begun—no reports of major damage have yet been issued. In advance of the storm's arrival, transportation to and from the region by both sea and air had been brought to a standstill. Early footage from Japan’s national broadcast station, NHK, show flooded streets in the capital, Naha, but little in the way of structural damage. Some damage can be expected from downed trees and flying debris, as well as to non-structural elements such as awnings and signage. Sanba may cause more extensive damage when it makes landfall on the Korean Peninsula. Some damage to non-engineered wood frame buildings is expected, particularly to roof envelopes. Engineered structures could suffer minimal damage to windows and cladding due to wind-borne debris. In South Korea, ships took shelter in ports and ferry services have been suspended in advance of the storm’s arrival. Sanba will be the third storm to affect South Korea in the last two months. On August 28, Bolaven made landfall north of Pyongyang, the capital of North Korea, resulting in 60 fatalities. The AIR tropical cyclone team continues to monitor Typhoon Sanba closely and will issue additional updates tomorrow, after the storm has crossed into the Korean Peninsula.

Pre-Landfall 1 | Downloads
Posting Date: September 17, 2012, 6:15:00 AM