Japan - Typhoon Shanshan

8 Aug 2018

Typhoon Shanshan will bring disruptive weather to much of northern and central Honshu as it makes a close approach to the island's east coast over the course of Aug. 8-9. As of 0000 JST Aug. 8, the system's center of circulation was located approximately 483 km (300 miles) southeast of Yokosuka, Kanagawa Prefecture. The latest forecast models suggest that, although the typhoon may not make actual landfall on mainland Japan, it will approach within about 90 km (56 miles) of Chiba Prefecture before turning northwards and closely following Honshu's east coast toward Sendai. Meteorologists project that Shanshan will begin weakening early Aug. 9 as it makes a second turn to the northeast, heading well back out to sea where it will diminish into an extra-tropical low northeast of Hokkaido by Aug. 10. 

Weather Warnings 
As of late Aug. 7, the Japan Meteorological Agency (JMA) is maintaining severe weather warnings and advisories for high waves, dense fog, thunderstorms, storm surges, and gale force winds in parts of eastern Honshu and Hokkaido. Authorities will likely issue new alerts or update/extend existing advisories as Shanshan draw closer - the proximity of the center of circulation to land will ultimately determine how significant the weather-related impacts will be. Current models suggest that Tokyo, as well as the Chiba, Fukushima, and Ibaraki prefectures, will likely be hardest-hit by inclement weather associated with the system. 

Hazardous Weather 
Parts of eastern Honshu from Shizuoka to Sendai, including the greater Tokyo area, will likely experience sustained winds of over 63 kph (39 mph) Aug. 8-9. Higher wind gusts of up to 115 kph (70 mph) are possible depending on the track of the storm. Widespread rainfall totals of 5-10 cm (2-4 inches) are likely in eastern Honshu, with the highest totals of over 13 cm (5 inches) possible in parts of Chiba and Shizuoka prefectures. Heavy rainfall could cause flash and areal flooding in low-lying communities near watercourses, as well as in urban areas with easily overwhelmed stormwater drainage systems. Sites located downstream of large reservoirs or rivers may be subject to flash flooding after relatively short periods of intense rainfall. Rain-induced landslides pose an additional threat in hilly or mountainous locations. 

Depending on Shanshan's track, moderate storm surge and coastal flooding are possible near the path of the center of circulation. Areas previously affected by heavy rainfall carry an elevated risk of inundation and/or debris flow, particularly where soil has become overly saturated. This risk extends to parts of eastern Japan that were recently impacted by the passage of Typhoon Storm Jongdari. 

Shanshan will contribute to ground, air, and maritime transport disruptions in eastern Japan through at least Aug. 10. Floodwaters may render some bridges or roadways impassable, impacting ground travel in and around affected areas. Strong winds could down trees or spread debris, which could damage infrastructure (including power lines) or impede access to important thoroughfares. Disruptions to rail transport, including underground networks, are possible during periods of severe inclement weather. High winds are likely to trigger flight delays and cancellations at regional airports, including - but not limited to - those serving Hakodate (HKD), Tokyo (HND, NRT), and Sendai (SDJ). Hazardous sea conditions could prompt the temporary suspension of ferry services and port operations, including in Ishinomaki Bay, Tokyo Bay, Sagami Bay, and the Tsugaru Straits. 

Disruptions triggered by inclement weather and resultant hazards, such as flooding, could persist well after conditions have improved. If there is severe damage to infrastructure, repair or reconstruction efforts may exacerbate residual disruptions. 

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