A typhoon is the regional term for a mature tropical cyclone that forms over the Northwest Pacific Ocean and affects East Asia, including the Japanese archipelago. These powerful weather systems are a recurring feature of the Japanese climate, bringing intense rainfall and destructive winds mostly during the late summer and early autumn. The Japanese word for this weather phenomenon is taifū, and the country maintains a sophisticated system to track and prepare for their arrival.
Understanding Typhoon Nomenclature and Structure
The name a tropical cyclone receives depends on where it forms, though the underlying meteorological process is the same. Storms in the North Atlantic and Northeast Pacific are called hurricanes, while those in the South Pacific and Indian Ocean are referred to as tropical cyclones. For Japan, located within the Northwest Pacific basin, the term typhoon is the standard.
These massive systems are powered by the energy released when warm, moist air rises from the ocean surface and condenses, forming towering clouds and creating a central area of extremely low pressure. The Earth’s rotation, known as the Coriolis force, causes the inflowing air to be deflected, resulting in the characteristic counterclockwise spin in the Northern Hemisphere. This rotation organizes the storm into distinct structural elements: the central, relatively calm eye; the surrounding eyewall of the most intense winds and rainfall; and the outer spiral rainbands.
The Japan Meteorological Agency (JMA) uses a distinct classification scale to communicate a storm’s intensity. The JMA classifies a tropical cyclone as a “typhoon” when its maximum sustained winds, averaged over 10 minutes, reach 118 kilometers per hour or more. Within this category, the JMA further differentiates by wind speed: a “Very Strong” typhoon has winds ranging from 157 to 193 kilometers per hour, and a “Violent” typhoon exceeds 194 kilometers per hour. Japan primarily refers to these storms by a number corresponding to the order of their formation in the year, rather than using personal names.
Geographical Patterns and Seasonal Timing
The typical typhoon season in Japan runs from May through October, with peak activity occurring during the late summer months of August and September. These storms originate in the warm waters of the Western Pacific and are steered north or northwest by atmospheric currents, often curving toward the Japanese islands. This timing coincides with the period when ocean water temperatures are highest, providing the necessary energy for these systems to maintain their strength.
Exposure to these storms is not uniform across the Japanese archipelago, as the southern islands are significantly more vulnerable to direct hits. Okinawa Prefecture, situated far to the south, frequently experiences the highest number of typhoons each year. Moving north, the larger main islands of Kyushu and Shikoku are the next most-affected regions. Honshu, the largest island, generally only experiences heavy rain and strong winds from weakened storms or those tracking far offshore. The northernmost island of Hokkaido is the least impacted, as typhoons often lose power over cooler waters before reaching it.
Japan’s Official Warning and Safety Systems
The nation’s primary defense against these storms is the warning system administered by the Japan Meteorological Agency (JMA). The JMA tracks the storms and issues various advisories and warnings based on forecast wind speeds and expected precipitation. This information is then integrated into a five-level alert system managed by local governments to guide public action.
The system starts with lower-level advisories that encourage citizens to check weather forecasts and prepare emergency kits. When a storm is imminent, local authorities issue a Level 3 warning, signaling the elderly, disabled, and others who require time to evacuate to move to a designated shelter. The most serious warning is a Level 4 Evacuation Order, which mandates that all residents in identified at-risk zones must immediately evacuate to a safe location.
Warning Levels
The JMA reserves the “Emergency Warning” for phenomena of extraordinary magnitude, such as a “Violent” typhoon, expected to significantly exceed regular warning criteria. A Level 5 alert is issued when a disaster is already occurring, urging people to take immediate safety measures to protect their lives, such as moving to the highest floor of a sturdy building.
Preparation
Citizens are advised to secure loose outdoor objects, stock up on food and water, and monitor official channels. Strong typhoons frequently cause widespread disruption to public transportation, including the suspension of high-speed rail and air travel.