Typhoons Facts: Tropical Cyclones in Northwestern Pacific

Facts about Typhoons

The summer weather brings with it the typhoons that lash the islands of the Northwest Pacific and the coastal regions of East Asia.

Just as the South Pacific cyclone season occurs during the Southern Hemisphere summer, so the Northwest Pacific’s typhoons are also most likely to strike when the weather is hottest and sea temperatures highest. In the Northern Hemisphere, the peak time for typhoons runs from June to November, parallel with the North Atlantic Hurricane Season.

No Defined Pacific Typhoon Season

Because the waters of the northwest Pacific where typhoons form are warm all year round, tropical cyclones can strike at any time. There is no ‘typhoon season’ as such, but the people of the region know that the summer is the time to be prepared.

The US State Department travel advisory signals for another year the increased likelihood that typhoons will affect Japan, Korea, Taiwan, China, South East Asia, and the islands that dot the Western Pacific Ocean north of the equator. According to the advisory, the region experiences an average of 31 typhoons each year, “about half of which have the potential to cause severe destruction.” The advisory provides solid common-sense advice and some useful links to learn more about the Pacific’s typhoons.

Typhoon Formation

Typhoons form at sea when the warm waters of tropical latitudes meet atmospheric conditions particularly conducive to an upsurge in wind strength, the system escalating as the air forced upwards rapidly cools. The resulting tropical depressions created by this combination of conditions then generates typhoons which follow a path that can range from straight towards land to the west, through to a westerly then north and east direction in a curved path. The further north the typhoon starts, the more likely it is to follow such a curved path, caught by the earth’s rotational effect known as the Coriolis force.

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The typhoon path and direction will naturally determine where they will strike populated areas. Typhoons on relatively straight courses that keep them in the lower latitudes pose a risk to the Philippines, South East Asia, and Southern China, while typhoons curving northwards may threaten Taiwan, Korea, and Japan.

All the combinations required for typhoon formation are rare in the non-summer months, but can nevertheless exist then as well.

Frequency of Pacific Typhoons

Advances in weather defense systems and early warning technology have meant that loss of life from tropical cyclones has reduced markedly over recent years. Nevertheless, typhoons still cause deaths each year, as well as considerable economic damage. The incidence of typhoons is a cause for considerable climate study, with the El Nino weather pattern shown to be a contributing factor in both the number of tropical storms in the northwestern Pacific and the path they tend to take.

The Tropical Storm Risk Consortium (TSR) comprises experts in the fields of insurance, risk management, and seasonal climate forecasting. According to a TSR report, the forecast for typhoons is for near-average activity. Intense typhoons (hurricane category 3 to 5) are calculated at a potential 9.2 compared to the average since 1965 of 8.6. Typhoons of lesser strength are forecast to be slightly below the long-term average.

TSR has also compiled a report showing that Northwest Pacific typhoons were 10% to 20% below the long-term average, with seven intense cyclones. The most destructive tropical storms were in the Philippines, where Ketsana in late September and Parma in early October killed over 600 people and caused US$300 million in damage.

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Mainland Japan’s only major typhoon of 2009 was Melor, which did damage estimated at US$1.5 billion. Morakot brought severe flooding to Taiwan in August, while Ketsana also caused fatalities in Vietnam, Cambodia, Thailand, and Laos.

Predicting Typhoons, Hurricanes, and Tropical Cyclones

A network of cyclone monitoring sites around the globe uses the latest satellite and weather radar technology to track and analyze cyclones as they develop. Complex computer modeling is used to predict the paths and impacts of cyclones. This scientific work has saved countless lives over recent decades, particularly in developed countries.

The United Nations agency World Meteorological Organization (WMO) plays an important role in overseeing the international framework under which national meteorological centers work together to help alert populations vulnerable to active typhoons and other tropical storms.

Predicting the path and possible destructiveness of typhoons is critical to preparing the general public for the coming onslaught. Equally important are the authorities’ ability to apply their civil defense procedures effectively, and their programs of rehabilitation once the typhoons have passed.


Wmo.int, Fact Sheets

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