Why Do Typhoon Tracks Suddenly Change Direction? What Is the Subtropical High?
Typhoons Don't "Move" on Their Own
A typhoon is essentially a vortex within the atmospheric river. Its movement is primarily "steered" by large-scale surrounding circulation patterns, with the most critical factor being the Subtropical High (Sub-High).
How the Sub-High Determines Typhoon Tracks
The Sub-High is a massive warm-core high-pressure system hovering over the Western Pacific. Typhoons typically move along its outer periphery:
- When the Sub-High is strong and positioned further west → The typhoon is steered westward into the South China Sea, affecting South China.
- When the Sub-High retreats eastward, creating a gap → The typhoon turns northward through the gap, affecting East China, Japan, and Korea.
- When the Sub-High splits into two rings → The typhoon moves slowly or spins in place within the saddle field.
Common Anomalous Tracks
- Looping/Stalling: Weak steering currents cause the typhoon to get "lost." For example, Typhoon Wayne in 1986 had a 23-day lifespan and looped three times.
- Sudden Westward Turn: A sudden strengthening and westward extension of the Sub-High.
- Binary Interaction (Fujiwhara Effect): Two typhoons within 1,000–1,200 km of each other exert mutual influence on their paths.
Why Forecasting Turns Is Difficult
The advance and retreat of the Sub-High are influenced by multiple systems, such as mid-latitude westerly troughs and the South Asia High. Numerical models often have significant errors in predicting the Sub-High's structure beyond three days. Therefore, track forecasts often show the greatest divergence around the turning point, so it is advisable to compare forecasts from multiple agencies.