Weather Administration Explains 'Mysterious Blue Line' on Wind Map is a Stationary Front Rain Band
Taiwan's Central Weather Administration explained that the "mysterious blue line" frequently appearing on recent wind forecast maps is actually a "front," where airflows from different directions meet. The northeasterly wind on the north side and the southwesterly wind on the south side collide, forming a low-wind-speed zone and forcing air to rise, which carries moisture upward, develops strong convection, and results in rainfall. This line is the stationary front commonly seen near Taiwan in May and June, and the weather around it is unstable and prone to intense rain, warranting public caution.
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- 📰 Published: June 10, 2026 at 21:28
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(CNA Website) A "mysterious blue line" that has recently appeared frequently near Taiwan on wind forecast charts has sparked public curiosity. The Central Weather Administration explained in a Facebook post that this blue line is actually a "front," a location where winds from different directions converge.
The administration pointed out that according to the legend on the right, the dark blue and purple colors represent weak horizontal wind speeds, so the blue line signifies a long, narrow "low-wind-speed zone." In this chart, the north side of the front has cooler northeasterly winds, while the south side has the southwesterly monsoon carrying large amounts of warm, moist air. When the two air currents meet here, they must "brake suddenly," forming a low-wind-speed zone where the wind speed approaches zero.
However, the airflow does not simply disappear. When two powerful air currents collide horizontally, they are forced to rise, sending moisture high into the atmosphere, which then develops into vigorous convection and brings rain. Therefore, the weather near the frontal zone represented by this blue line is usually more unstable and is a hot zone for intense convective rainfall.
The administration stated that this airflow convergence line tends to appear near Taiwan in May and June each year, which is the stationary front often heard about recently. The administration reminds the public to remember to bring rain gear when they see this keyword and to pay attention to alerts issued by the Weather Administration. (Editor: Wang Chia-yu) 1150610
The administration pointed out that according to the legend on the right, the dark blue and purple colors represent weak horizontal wind speeds, so the blue line signifies a long, narrow "low-wind-speed zone." In this chart, the north side of the front has cooler northeasterly winds, while the south side has the southwesterly monsoon carrying large amounts of warm, moist air. When the two air currents meet here, they must "brake suddenly," forming a low-wind-speed zone where the wind speed approaches zero.
However, the airflow does not simply disappear. When two powerful air currents collide horizontally, they are forced to rise, sending moisture high into the atmosphere, which then develops into vigorous convection and brings rain. Therefore, the weather near the frontal zone represented by this blue line is usually more unstable and is a hot zone for intense convective rainfall.
The administration stated that this airflow convergence line tends to appear near Taiwan in May and June each year, which is the stationary front often heard about recently. The administration reminds the public to remember to bring rain gear when they see this keyword and to pay attention to alerts issued by the Weather Administration. (Editor: Wang Chia-yu) 1150610
FAQ
風場預測圖上的「神秘藍線」是什麼？
根據中央氣象署的解釋，這條藍線代表「鋒面」，是不同風向（北側的東北風與南側的西南季風）氣流交會的位置，會形成一條狹長的低風速帶。
為什麼這條藍線會帶來降雨？
因為兩股強大的氣流在水平方向相撞後，會被迫往上抬升，將潮濕水氣送上高空，進而發展出旺盛的對流，形成降雨熱區。
這條藍線代表的鋒面在台灣什麼時候常見？
這種氣流交會線就是「滯留鋒面」，每年5、6月容易出現在台灣附近。
看到這條藍線代表天氣會如何變化？
代表鋒面帶附近的天氣通常較不穩定，容易出現劇烈對流與降雨，提醒民眾出門需攜帶雨具並留意氣象資訊。
這條藍線區域的風速有什麼特徵？
它是一條狹長的「低風速帶」，因為兩股氣流在此交會時需要「緊急煞車」，導致風速趨近於0。