Navigable semicircle

In the Northern Hemisphere, it refers to the left semicircle (right in the Southern Hemisphere) in the direction of travel of a typhoon or developed low pressure system. The winds blowing into the center cancel out the winds caused by the movement of the typhoon or developed low pressure system itself, so the winds are relatively weaker and the waves are lower than in the right semicircle. When a ship in the navigable semicircle tries to move away from the center to take refuge, it receives a tailwind, making it easier for it to escape, so it is also called the tailwind semicircle.

[Yo Narumura]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

北半球では台風や発達した低気圧の進行方向に対して左側の半円（南半球では右側）のことをいう。中心に吹き込む風と、台風や発達した低気圧自身の動きによる風とが相殺するので、右側の半円に比べ比較的風が弱く、波高も低くなる。可航半円にいる船舶が避難のため中心から遠ざかろうとするときには追い風を受け脱出しやすいので、追い風半円ともいう。

［饒村　曜］

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