無風三尺浪 [无风－－－]

Jyutping mou4 fung1 saam1 cek3 long6
Pinyin wú fēng sān chǐ làng

Definitions (CC-CEDICT)
  1. lit. large waves in windless conditions (idiom)
  2. fig. trouble arising unexpectedly
Definitions (CC-CANTO)
  1. (Cantonese analogy - figurative meaning) something happen suddenly without any forewarning