Tropical Storm Nangka Batters Japan with Heavy Rain, High Winds: AIR Report

July 20, 2015

Catastrophe modeling firm AIR Worldwide’s report on Typhoon Nangka notes that it “made landfall July 16, 2015, at 23:07 Japan Standard Time (JST) (14:07 UTC) with a central pressure of 965 mb near Muroto City, on the eastern coast of Shikoku Island, Japan. It was the 11th typhoon of the season.

According to AIR, “typhoons are the most frequent type of natural disaster to cause property loss in Japan. While winds are typically the predominant driver of loss from most typhoons, Japan does have strict and well-enforced construction codes and significant structural damage from Nangka is unlikely.

“In Japan, wind damage is typically automatically covered under standard fire insurance policies, but flood damage is not, despite the fact that Japan regularly experiences “wet” storms that deliver extreme precipitation and flooding that contribute substantially to damage. Property owners who want flood coverage can purchase it as an add-on to a standard policy or select a comprehensive policy.”

Dr. Anna Trevino, scientist at AIR Worldwide, noted that “maximum sustained wind speeds were estimated at just over 120 km/h (75 mph) at landfall, the equivalent of a Category 1 tropical cyclone on the Saffir-Simpson scale.

“The storm moved slowly northward across Shikoku and made a second landfall at Kurashiki in the Okayama Prefecture just past 6:00 a.m. JST on July 17, 2015, (21:00 UTC, July 16, 2015) with maximum sustained winds of 80 km/h (50 mph). As of 12:50 UTC Nangka had a forward speed of 25 km/h (16 mph), and had moved off Tottori Prefecture. Nangka continues to impact Japan with tropical storm–force winds and torrential rain. Sustained winds were estimated at 65 km/h (40 mph) with gusts of 90 km/h (56 mph).”

AIR’s report said the “highest wind gust reported was 153 km/h (95 mph), at Muroto just before midnight on July 17, JST, about an hour after the storm made landfall. Sustained winds in the area reached 122 km/h (76 mph). A wind gust of 124 km/h (77 mph) was recorded at Komatsushima Air Base in Tokushima Prefecture, at 3:24 a.m. JST on July 17. In Nagoya, winds reached 74 km/h (46 mph), while Tokyo reported winds up to 58 km/h (36 mph). Winds reaching 63 km/h (39 mph) affected several other cities including Osaka.”

In addition the report explained that as the storm interacted with the mountainous regions of Japan and a stationary front, “it produced extremely heavy rainfall. Rainfall rates reached 77.5 mm/h [3 inches per hour] in Kawauchi, Fukushima Prefecture. In Kamikitayama, south of Osaka, 740 mm [just under 29 inches] of rain has already fallen, while 690 mm [26.91 inches] has fallen in Odie, Mie Prefecture. Umaji, Kochi Prefecture, has reported rainfall totals of 660 mm [25.74 inches]. Sediment disaster alerts (landslides) have been issued for south-central coastal areas, including Tokyo.”

Dr. Trevino indicated that “tropical Storm Nangka is expected to continue moving northeastward through the Sea of Japan and weaken due to increasing vertical wind shear and continued interaction with land. Strong winds and torrential rain are expected to impact both coasts of Japan during the next few days, with warnings issued for central and south-central areas of Honshu, including the cities of Osaka, Kyoto, Nagoya, Kobe, and Toyko. The affected region includes several other cities such as Kochi, Oita, and Okayama. Rough winds have created dangerous surf along much of both the eastern and western coastlines of Japan.”

AIR also noted that the “storm is impacting all of Japan’s main islands, with warnings issued for the south-central areas of Honshu, including Osaka, Kobe, Nagoya, and other major cities. The warnings are also in effect in Tokyo, which has been impacted with heavy rains and flooding. Prior to the storm 4,000 people were evacuated from Kochi Prefecture due to the potential of mudslides.

“On Thursday, approximately 500,000 were advised to evacuate; currently evacuation is advised for nearly 100,000 people located in western Japan. In Kobe, more than 30,000 households have been advised to evacuate. Government officials are warning that some areas could see up to 1 meter of rainfall. Up to 25 mm per hour was still falling in some areas as of July 17.

“Reported building damage has been mostly due to flooding, although several homes have also reported some wind damage. About 130 homes have flood damage, mostly in the prefectures of Tokushima, Wakayama, and Tochigi, although some have been reported in Tokyo. Nearly 60 homes, mostly in Tokushima Prefecture, have reported flood damage above the first floor level.

Dr. Trevino concluded with a warning from the Japan Meteorological Agency, which “is forecasting heavy rains to continue over the next few days bringing continued risk of flooding and landslides.”

Source: AIR Worldwide

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