要= will! 好像要下雨了= It looks like it will rain.

In addition to what Beth mentioned, "要 ... 了" is an expression to indicate a future event.

“要”表示一种推测，“下雨了”是在陈述事实。

这里的"要"是“马上”，“就快要” 的意思哦。

要 is tricky. It can mean: --want （我要去, I want to go.) --must （我要去, I want to go. -- though Mainlanders might tend to use 得 instead) --will (simple future: I will go, usually with a time expression like 我 明天 要去她家。） Most beginning textbooks ignore the multiple meanings, but if you start reading level-appropriate stuff, you'll encounter all these meanings all mixed up, all the time.