Typhoon

A typhoon is a powerful storm that forms between 180° and 100°E in the Northern Hemisphere. These storms have very strong winds, at least 119 km/h (74 mph), and are called typhoons in a region known as the Northwestern Pacific Basin. This area makes up almost one third of all the world's storms like this.

The Pacific Ocean is split into three parts for tracking these storms. The main office for giving out weather forecasts for typhoons is in Japan. Other groups that help watch for typhoons are in Hawaii, the Philippines, and Hong Kong. These groups work together to name the storms.

Typhoons can form at any time of the year in this part of the world, but they are most common between June and November. They need warm ocean water, moist air, and other weather conditions to develop. On average, this area sees more typhoons than any other place on Earth. The Philippines often feels the biggest impact, but China and Japan are also affected. Some of the worst typhoons in history have hit China. From 1950 to 2022, this region had about 26 named storms each year, with around 17 of them becoming strong typhoons.

Nomenclature

Etymology

The word "typhoon" may have come from Chinese or Persian-Hindustani languages.

One idea is that it comes from the Chinese words for "winds which last long." These words were first used in China in the year 1124. Over time, the words changed and were used in different parts of China. Foreign sailors later used the word "typhoon."

Another idea is that "typhoon" comes from a word in Persian and Hindustani that means "storm." This word may have come from an ancient Greek story about a creature named Typhôn. The word appeared in French in 1504 and in English books as early as 1588.

Intensity classifications

See also: Tropical cyclone scales

A tropical depression is the smallest kind of tropical storm. It has wind speeds up to 33 knots (38 mph; 61 km/h). When the winds grow stronger than 34 knots (39 mph; 63 km/h), it becomes a tropical storm and gets an official name.

If the storm gets even stronger, with winds of 48 knots (55 mph; 89 km/h), it is called a severe tropical storm. When the winds reach 64 knots (74 mph; 119 km/h), it is called a typhoon, the strongest category used by the Japan Meteorological Agency.

Since 2009, the Hong Kong Observatory has used three levels for typhoons: typhoon, severe typhoon, and super typhoon. A typhoon has winds from 64–79 knots (74–91 mph; 119–146 km/h). A severe typhoon has winds of at least 80 knots (92 mph; 150 km/h). A super typhoon has winds of at least 100 knots (120 mph; 190 km/h).

The United States' Joint Typhoon Warning Center sometimes calls typhoons with winds of at least 130 knots (150 mph; 240 km/h) "super typhoons." However, they measure winds over a shorter time than the Japan Meteorological Agency, which can make their numbers look higher.

Genesis

See also: Tropical cyclogenesis

For a typhoon to form, there are six important things needed: warm ocean water, unstable air, lots of moisture, enough turning force to create a low-pressure center, a starting point or disturbance, and calm winds high up in the sky. Warm ocean water, about 26.5 °C or higher, is very important because it helps keep the storm strong. The storm also needs to be at least 500 km away from the equator.

Most typhoons start in a special wind pattern called the monsoon trough. Even with the right conditions, a storm won’t form without a starting point near the ocean surface. The winds high up in the sky also need to be calm for the storm to develop well. Usually, typhoons in the Pacific have two streams of air moving away from the storm, one going north and one going toward the equator.

Frequency

Nearly one-third of the world's big storms called tropical cyclones start in the western Pacific Ocean. This area sees the most storms of all places on Earth. These storms, known as typhoons, can form any time of the year but are most common from August to October, matching the busy months for storms in the Atlantic hurricane seasons. This area also sees some of the strongest storms ever recorded.

In the Philippines, there are fewer storms in February, but the number grows each month until it peaks from July through October, with September being the busiest month for these storms around the archipelago. Even though storms slow down in November, some very strong ones can still happen, like Typhoon Haiyan. The parts of the Philippines most often hit by these storms are northern and central Luzon and eastern Visayas.

Paths

See also: Monsoon trough

Most big storms called typhoons start on the side closer to the equator and then move toward the north. They often form in a special area in the northwest Pacific Ocean called typhoon alley. When the subtropical ridge shifts due to El Niño, the paths of these storms also change.

Typhoon paths usually go in three ways:

• A straight path that affects the Philippines, southern China, Taiwan, and Vietnam.
• A curved path that affects the eastern Philippines, eastern China, Taiwan, Korea, Japan, and the Russian Far East.
• A path going straight north, only affecting small islands.

A very few storms, like Hurricane John, can become typhoons if they move from the Eastern/Central Pacific into the western Pacific.

Basin monitoring

Within the Western Pacific, the RSMC Tokyo-Typhoon Center, part of the Japan Meteorological Agency, has been in charge of giving warnings for the whole area since 1989 and naming storms since 2000. Each country's weather service is responsible for warnings about tropical storms that could affect their land. For example, the Philippine Atmospheric, Geophysical and Astronomical Services Administration handles warnings for the Philippines, and the Hong Kong Observatory does so for Hong Kong.

Names for typhoons come from 14 southeast and east Asian countries and regions, as well as the United States. These names are listed in a specific order and are used one after another. If a typhoon causes damage, the affected area can ask to retire the name, and a new one is chosen. Typhoons are usually named after animals, flowers, or signs of the zodiac, though the Philippines uses both human names and other objects. Japan and some other countries also number the typhoons. Storms moving from the central Pacific keep their original name but are called typhoons instead of hurricanes.

Records

The year with the most typhoons in the Western Pacific was the 1964 Pacific typhoon season, when 39 storms formed. Usually, there are around 15 seasons with 30 or more storms. The year with the least typhoons was the 2010 Pacific typhoon season, with only 14 storms.

The strongest typhoon ever recorded was Typhoon Haiyan, with winds reaching 314 km/h (195 mph) before it hit the central Philippines in 2013. Typhoon Tip in 1979 was the most powerful typhoon by pressure, with a minimum pressure of 870 hectopascals. Typhoon Morakot in 2009 caused huge amounts of rain in Taiwan, flooding many areas and breaking rainfall records.