意思不同： here it comes 它到了，强调已经“到来”的动作
here it is coming 它就要到了，强调即将到来的动作
如：
Look! Here the bus is coming!
瞧！公交车就要来了！公交车（跟其他多个事件正在发生一样）
Look! Here comes the bus!
瞧！公交车（果然按时）来了！
在英语里，谓语动词经常由【助动词（be have has had did does do will shall等）+ 行为动词】来构成，比如：
The bus is coming.
The bus has come.
The bus will come
