What Is the Structure of a Typhoon? Dissecting the Eye, Eyewall, and Spiral Rainbands
A mature typhoon consists of three parts from the inside out: the typhoon eye, the eyewall, and spiral rainbands. The most intense wind and rain are not at the center, but in the eyewall region.
The Three-Layer Structure of a Typhoon
From satellite imagery, a mature typhoon resembles a giant rotating disk, typically 600–1,000 km in diameter. It is divided into three parts from the inside out:
1. Typhoon Eye (approximately 10–60 km in diameter)
The calm zone at the center of the typhoon. Subsiding air clears clouds and rain here, sometimes even revealing blue sky and stars. Although atmospheric pressure is at its lowest, the sea surface may still experience massive waves (as swells from all directions converge here).
2. Eyewall (the ring-shaped cloud wall surrounding the typhoon eye)
The most intense region of the entire typhoon—the strongest winds and heaviest rainfall occur here. The eyewall is composed of vigorous convective cloud towers that can reach heights of over 15 km. The "maximum wind speed near the center" mentioned in typhoon warnings actually refers to conditions within the eyewall.
3. Spiral Rainbands (extending hundreds of kilometers outward)
Banded rainfall areas rotating around the center, spiraling inward from the periphery. The intermittent weather experienced during a typhoon, characterized by bursts of heavy rain followed by lulls, results from these spiral rainbands passing over one by one.
Why You Should Not Go Outside When the Typhoon Eye Passes Over
When the typhoon eye passes over, wind and rain suddenly cease, leading many to mistakenly believe the typhoon has passed. In reality, this calm may last only tens of minutes. Subsequently, the eyewall on the opposite side arrives, instantly restoring gale-force winds and torrential rain with reversed wind direction—posing a severe risk of injury to those caught off guard. The correct approach is to wait until meteorological authorities officially lift the warning before going outside.
Eyewall Replacement Cycle: The "Tire Change" Process of Strong Typhoons
Strong typhoons often exhibit a "double eyewall" phenomenon: a new outer eyewall forms while the inner old eyewall gradually dissipates. During the replacement cycle, intensity temporarily weakens; once completed, the eyewall radius increases, expanding the range of strong winds. This is one of the challenges in forecasting typhoon intensity changes and is a common source of discrepancies among different agencies' forecasts featured on TyphoonSays.