What's the weather like in mid-February in Vietnam?

It's cold in the north (near Hanoi), and it's ok to wear a long-sleeved T-shirt with a thick velvet coat. It's hot in the south, and it's also ok to wear a short-sleeved T-shirt. Except for Datuk, it's relatively high above sea level in other places, so it's cold (especially at night, it's not cold during the day, at least it's thick velvet at night, afraid of cold, and it seems colder to sit behind someone else's motorcycle, so,