The 2015 Northwest Pacific Typhoon Season: Already a Record-Breaker

While the Atlantic hurricane season is expected to be below average this year, the North Pacific is smashing records. Fuelled by the strengthening El Niño conditions, the Accumulated Cyclone Energy (ACE)—used to determine how active a season is by measuring the number of storms, their duration and their intensity—continues to set unprecedented highs for the 2015 season.  According to Dr. Philip Klotzbach, a meteorologist at Colorado State University, the North Pacific ACE is 30% higher for this time of year than at any other time since 1971.

Philip J. Klotzbach, Colorado State University

To date, there have been 12 named Northwest Pacific storms, of which three have strengthened to Category 5 super-typhoon status, and two have strengthened to Category 4 typhoon. Typhoon Maysak was the first of the super-typhoons to develop and is reportedly the strongest known storm to develop so early in the season—it eventually passed over the northern Philippines in late March as a tropical depression. Super-Typhoons Noul and Dolphin followed in quick succession in May, with Noul scraping the northern tip of the Philippines, and Dolphin tracking directly in-between the islands of Guam and Rota.

China is recuperating after getting hit by Typhoons Linfa and Chan-Hom only days apart. Linfa made landfall on July 9, bringing strong winds and heavy rainfall to Hong Kong and southern China’s Guangdong province. Two days later, Chan-Hom brought tropical storm-force winds and heavy rainfall to Taiwan and the Japanese Ryukyu Islands before briefly making landfall as a weak Category 2 storm over the island of Zhujiajian in the Zhejiang province. Prior to landfall, Chan-Hom was anticipated to pass over Shanghai, but swung northeast and missed China’s largest city by 95 miles. Despite this near-miss, Chan-Hom still stands as one of the strongest typhoon to have passed within 100 miles of the city in the past 35 years.

Typhoon Nangka, the first typhoon to hit Japan this season, intensified to a Category 4 storm before ultimately making landfall as a Category 1 storm over the Kochi Prefecture on Shikoku Island, Japan. Although Nangka’s strength at landfall was weaker than originally forecast, the high level of moisture within the system caused significant rainfall accumulations, leading to widespread flooding and the threat of landslides. While there was an initial fear of storm surge in Osaka Bay, there has been limited damage reported.

This record-breaking season has been strongly influenced by the strengthening El Niño conditions, which can be characterised by several physical factors including warmer sea surface temperatures, a higher number of Category 3-5 typhoons, and a greater proportion of typhoons that follow recurring or northward tracks—all of which have been evident so far this year.

With El Niño conditions expected to continue intensifying the storms to come, this season highlights the necessity for a basin-wide multi-peril model, connected through an event-based approach and correlated geographically through a basin-wide track set. These will be featured in the new Japan typhoon model, due out next year, followed by the South Korea and Taiwan typhoon models. The RMS China typhoon models currently models typhoon wind, inland flood and surge for a correlated view of risk.

As El Niño conditions continue to bolster the Northwest Pacific typhoon season, RMS will be monitoring the situation closely. In September, RMS will be releasing a white paper on ENSO in the West Pacific that will provide further insight into its affects.

Manager, Business Solutions, RMS
As a member of RMS' model solutions team, Nikki works to guide more informed usage of catastrophe models and enhance understanding of model uncertainty. This requires interaction with the market, as well as other important stakeholders such as regulators and rating agencies, to help RMS develop tools that capture the evolving needs of the risk management industry. Based in London, her primary focus is on supporting the RMS Asian modeling suite and in facilitating client understanding of catastrophe models for risk management in the region. Nikki holds a BSc in Physical geography from Liverpool John Moores University and an MSc Geophysical hazards from University College London

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