Vietnam has a hot and humid climate, influenced by seasonal monsoons. The climate in the south is equatorial, while the north is sub-tropical. Climate differences also depend on altitude. Common sayings: Đông sao thì nắng, vắng sao thì mưa (dense stars announce sunny weather; scattered stars are signs of rain). Chuồn chuồn bay thấp thì mưa (when dragonflies fly low, it will rain). Nắng tốt dưa, mưa tốt lúa (sun is good for watermelons, rain is good for rice plants). Lúa chiêm lấp ló đầu bờ, hễ nghe tiếng sấm phất cờ mà lên (summer rice plants peeping from behind the borders of rice-fields, rise at the first sound of thunder like standards floating in the wind). Gió đông là chổng lúa chiêm; heoheo gió bắc là duyên lúa mùa (the east wind is good for summer rice, the north wind is good for winter rice). Chớp Dông nhay nháy, gà gáy thì mưa (if lightning flashes in the east at night, it will rain at cock’s crow).
Trăng quầng thì hạn, trăng tán thì mưa (a halo around the moon is a sign of drought; diffused moonlight means it will rain). Mống dài trời lụt, mống cụt trời mưa (a long rainbow announces a flood, a short rainbow is a sign of rain). Gió bấc hiu hiu, sếu kêu thì rét (when the north wind blows and cranes fly across the sky, it will be cold). Nắng chóng trưa, mưa chỏng tối (when it is sunny, the moon comes sooner; when it rains, night falls more quickly). Ráng vàng thì nắng, ráng trắng thì mưa (golden cloud on the sky-line means sun, white cloud means rain). Gió heo may chuồn chuồn bay thì bão (when the wind blows and dragonflies fly, there will be a typhoon). Mùa hè dang nấng, cỏ gà trắng thì mưa (on sunny summer days, if the roots of the couch-grass turn white, it will rain). Đêm tháng Năm chưa nằm đã sáng, ngày tháng Mười chưa cười đã tối (in nights of the 5th lunar month (summer), it is light before you lie down to sleep; in days of the 10th month [winter], it is dark before you laugh).
