AIR Worldwide Discusses Expected Damages From Typhoon Phanfone

October 6, 2014

An ominous storm from the outset, Typhoon Phanfone is now on track to impact large areas of Japan with damaging winds and substantial rainfall, from Osumi and the southeastern coast of Kyushu to Shikoku and Honsh, according to Boston-based catastrophe modeling firm AIR Worldwide.

Although no longer a super typhoon, Phanfone is expected to cause widespread disruption as it proceeds northeastward toward Tokyo.

Mount Ontake, the site of a deadly volcanic eruption September 28, is predicted to receive heavy rainfall that will result in dangerous debris and ash flow.

According to the Japan Meteorological Agency (JMA), Phanfone was located at 31.1 N 132.9 E, as of 11 UTC 5 October. The JMA estimates that Phanfone has a minimum central pressure of 945 mb and maximum 10-minute sustained wind speeds of ~92 mph.

“Despite remaining offshore of the Japanese mainland, Phanfone has produced impressive rainfall totals throughout a large portion of Japan,” said Dr. Kevin Hill, senior scientist at AIR Worldwide.

“Nakatane, in Kagoshima prefecture, recorded 340.5 mm of precipitation in the 48-hour period preceding 11 UTC 5 October. Portions of Tokyo have already received over 300 mm, well in advance of Phanfone’s center. Current wind speeds across Japan are modest, since the center of Phanfone remains offshore. The strongest reported wind gust at 11 UTC was ~50 mph, in Kochi prefecture. Earlier, Phanfone did produce wind gusts of up to ~100 mph in North Daito Island,” he said.

‘Phanfone is expected to rapidly transition into a strong cold-core low-pressure system in the next 24 hours, as it enters the mid-latitude baroclinic zone and encounters increasing wind shear, he said. “While increasingly hostile environmental conditions and the extra tropical transition process will cause Phanfone’s maximum wind speeds to decrease, the storm will still be capable of producing very heavy rain and strong winds well away from its center.”

According to AIR, at the expected wind speed levels, non-engineered structures may experience some damage to roof covering damage. Some poorly constructed wood-frame homes may experience moderate to high-level cladding and roofing damage, involving loss of roof covering, as well as the removal of porch coverings and awnings, and some these homes can even be destroyed.

Masonry homes and well-constructed wood-frame homes could have some damages to roof covering (tiles or shingles), wall siding, soffit panels, and gutters. Some poorly built and poorly maintained industrial buildings can lose roofing and siding, especially from windward corners, rakes, and eaves and can even collapse. For engineered structures, structural damage is not expected. Some apartment building and shopping center roof coverings could experience moderate levels of damage, and wall sidings may also experience some moderate levels of wind damage.

Perhaps a greater threat is damage from flooding, which will vary 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.

Water damage to machinery and contents drives most flood loss; because damage is usually limited to the lower stories of a building, high-rise buildings will experience a lower damage ratio than low-rise buildings because a smaller proportion of the building is affected.

According to AIR, typhoons are the most frequent cause of property loss in Japan. Winds are the predominant driver of loss, although Japan does have strict and well-enforced construction codes.

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 they can select a comprehensive policy.

Source: AIR Worldwide

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