Most years, the typhoon season peaks in September, as illustrated by the recent Typhoon No. 9, called Fitow, which killed two, and Typhoon No. 11, also known as Nari, which approached Okinawa last week.

The seasonal turbulence remains a threat to Japan despite improvements in meteorological satellites and weather forecasting technology — and some experts theorize that global warming may have altered its characteristics.

Following is some basic information on typhoons:

How many typhoons are there annually?

The Meteorological Agency defines a typhoon as any tropical cyclone with wind speeds above 61.9 kph and is generated in a U-shaped area surrounded by the international date line, 100 degrees east longitude and the equator.

The major distinction between typhoons and hurricanes, which affect Central and North America, is in their place of origin.

According to the Meteorological Agency, there was an average of 26.7 typhoons a year between 1971 and 2000, with 10.8 of them reaching within 300 km of the Japanese archipelago. During this time span, an average of 2.6 typhoons made landfall annually.

Why is September considered the peak of the typhoon season in Japan?

In fact, statistics show that more typhoons develop in August than in any other month, but weather conditions in September in the vicinity of Japan help them reach the archipelago.

While typhoons prior to the peak season have a propensity to head westward because of the powerful trade wind, in September the presence of high pressure systems in the Pacific area pushes the turbulence northward. Typhoons are then blown eastward toward Japan due to strong winds blowing from continental Asia.

In addition, typhoons in September tend to join forces with autumn’s seasonal precipitation front above Japan.

What was the most destructive typhoon ever to hit Japan?

The worst typhoon in recorded history was 1959’s Typhoon No. 15, later named the “Ise-wan” (Ise Bay) Typhoon by the Meteorological Agency. The colossal storm, which at times generated wind speeds of more than 180 kph, made landfall in Wakayama Prefecture on Sept. 26. It took 5,098 lives and left nearly 39,000 people injured, while 40,000 houses and buildings were completely destroyed. It was the largest number of deaths caused by a natural disaster in Japan until the 1995 Great Hanshin Earthquake killed 6,434 people.

Experts have suggested that the damage caused by the Ise-wan Typhoon was aggravated by the geographical characteristics of Ise Bay, which induced high storm surges, and a lack of disaster-prevention measures by the central and local governments.

How strong are typhoons?

Studies show that the energy unleashed by an average typhoon can reach a force 100 times greater than that generated by the atomic bomb dropped on Hiroshima.

However, the force of typhoons usually wanes through friction with sea or land surfaces, and is also influenced by temperatures and wind force in the surrounding atmosphere.

What is the driving force of a typhoon?

Typhoons are typically formed in areas with water temperatures above 27 degrees, because their power source is latent heat, or the energy released from vaporized water when it condenses and forms clouds, and which stimulates a typhoon’s formation.

Warm ocean water not only nourishes the turbulence but also heats the surrounding air. Because a high temperature is equal to lighter air, such a condition decreases air pressure in the area and causes winds to blow inward.

Does global warming influence the size or frequency of a typhoon?

In theory, global warming will facilitate typhoon development as it expands areas with high water temperatures. Some experts suggest that recent destructive hurricanes, including Katrina and Rita, were strengthened by global warming.

Takehiko Yamamura, author of more than 10 books on disaster prevention and the director of the private think tank Disaster Prevention System Institute, warns that the higher the water temperature near Japan gets, the more power a typhoon can sustain before striking the country.

However, other studies suggest the opposite and argue that warmer climates may diminish typhoons, because high temperatures tend to spawn various wind speeds and wind directions at different altitudes in the atmosphere. Such conditions, known as wind shear, are believed to spread, and therefore weaken, the power of hurricanes and typhoons.

Although a report by the Meteorological Agency in 2005 indicated that ocean temperatures have risen 0.48 degree in the last 100 years, no definitive conclusion has been made regarding the effect that global warming has on typhoons.

Can typhoons be tamed?

Unlike earthquakes, which are erratic, typhoons have become predictable because of the improvement in meteorological forecasts — and there have been attempts to tame them before they cause further damage.

One method tried by the U.S. government’s National Oceanic and Atmospheric Administration between 1962 and 1983 was to scatter iodide from an airplane in the air surrounding a hurricane when it developed over the ocean. Theoretically, the tactic would diffuse the power of the hurricane through premature precipitation.

However, the experiments, known as “Project Stormfury,” did not provide any definitive conclusions.

In Japan, studies to modify typhoons have been halted because of concerns over the possible decrease of annual precipitation.

How are typhoons named?

Beginning in 2000, typhoons which originate in the northwest Pacific or South China Sea have been named by a Typhoon Committee consisting of the Economic and Social Commission for Asia and the Pacific, and the World Meteorological Organization.

This group includes Japan and 13 other Asian countries, and employs a list with some 140 names on it, starting with “Damrey” (elephant in Thai) and running through “Saola” (the name of a rare antelope in Vietnamese).

Fitow, the name given the recent typhoon that hit Japan, was the 37th name on the list. It means flower in the Yapese language used in Micronesia.

What can we do to prevent damage?

Although typhoons caused thousands of deaths from the 1930s to 1950s, advancements in disaster prevention, such as positioning breakwaters, have reduced their potential for damage, according to Yamamura of the Disaster Prevention System Institute.

“It is still vital that each and every one of us has a handle on the area they live in, including the location of nearby rivers,” he said. “Emergency goods such as radios should be stockpiled as well.”

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