number unobtainable signal

• 空号信号

number unobtainable signal的用法和样例：

例句

1. Winds did not strengthen appreciably after the Strong Wind Signal came into effect, but due to the storm most places saw a wind direction changing to NE.
   三号信号发出后本地风势并没有明显增强，但风向已逐渐转向东北。