What is a Typhoon Wind Circle? How to Interpret the 7, 10, and 12-Level Wind Circles?

The meaning of wind circle radii and defense guidelines.

Wind Circles: The "Sphere of Influence" Map of a Typhoon

In typhoon warning information, the Level 7, Level 10, and Level 12 wind circles refer to the radius of the area surrounding the typhoon center where the average wind speed reaches that specific level (measured in kilometers). It answers a straightforward question: At what distance from the typhoon center will winds of a certain strength be experienced?

• Level 7 Wind Circle (≥13.9 m/s): Entering this range means significant strong winds begin. Tree branches may snap, walking becomes difficult, and marine operations must cease.
• Level 10 Wind Circle (≥24.5 m/s): Destructive gale-force winds. Simple structures begin to suffer damage, and people should stay indoors.
• Level 12 Wind Circle (≥32.7 m/s): Hurricane-force destruction. This is the core impact zone for direct hits and the primary focus for defensive measures.

Why Are Wind Circles Drawn as "Irregular Circles"?

The wind circles you see on TaifengSays track maps are often irregular shapes with different radii in four quadrants: for instance, the northeast radius might be 300 km, while the southwest is only 150 km. There are three main reasons for this:

• Movement Superposition: In the Northern Hemisphere, wind speeds on the right side of the typhoon's forward path are superimposed with its movement speed, making the right semicircle naturally larger.
• Asymmetric Environmental Flow: Features like the edge of the Subtropical High or monsoon surges can "fuel" winds on one side more than the other.
• Land Friction: The wind circle on the side closer to land is weakened and contracted due to terrain friction.

Therefore, do not just look at how far the typhoon center is from you; check which quadrant you are in. Even if the distance to the center is the same, cities located on the side with the larger wind circle may suffer much heavier impacts.

How to Use Wind Circles for Defense Decisions?

• Open the typhoon track map and identify the relationship between your city and the forecast path + swept area of the wind circles.
• If the Level 7 wind circle will sweep over → Stop outdoor activities, secure and store loose items.
• If the Level 10 wind circle will sweep over → Avoid going out unless necessary, check windows and doors, and prepare for potential power outages.
• If the Level 12 wind circle will sweep over → This indicates a direct hit. Follow government evacuation orders and stay away from windows.

The Relationship Between Wind Circles and Warning Signals

Local typhoon warning signals (Blue, Yellow, Orange, Red) are issued based on the estimated time of impact from the wind circles: A blue warning is typically triggered when an area is expected to be affected by the Level 7 wind circle within the next 24 hours, while an orange warning may be upgraded if the Level 10 wind circle is expected to impact within 12 hours. By learning to read wind circles, you can prepare "half a step ahead" of the official warnings.

A Common Misconception

Wind Circle Radius ≠ The Entire Size of the Typhoon: Some typhoons are small in size but have an extremely powerful core (e.g., Faxai in 2019), while others are massive with wind circles spanning thousands of kilometers but have a loose core (e.g., the later stages of Mangkhut in 2018). The defense priorities for "Small Steel Cannons" versus "Big Fatties" are completely different—the former requires protection against core wind forces, while the latter requires protection against prolonged wind, rain, and storm surges.