Why, hello there. Basically, it means "Hello.(with a hint of surprise)"The usage is kind of old. It's used less frequently in the U.S. these days. It's similar to how we might say "Oh/well/ah, hello there". We don't have to say well, oh, why, or ah. Sometimes we do use them to indicate surprise. We tend to use "Why, hello there." in a playful manner. As for the origin, I have no idea. Let's say you're watching a show on tv. On the show, a breathtakingly gorgeous woman walks over to the bar to sit down. There's also a man there and when he notices her he says, "Why, hello there beautiful. " Perhaps he said that because he was either a. surprised to see someone, b. surprised(and delighted) to see such an attractive woman or, c. both a and b. Let me give you another example. Let's say you see someone who you haven't seen in a very long time. You could say, "Why, if it isn't Bob Barker! " You would include "why" to show your surprise. I hear older people use it sometimes. People over the age of 40, I'd say. It might depend on where the person lives. I live in the southern part of the U.S. and I've heard it used in this situation many times.

The expression means, I am happily surprised to see you at this moment.

One meaning of 'why' is as an interjection. From dictionary.com: interjection 7. (used as an expression of surprise, hesitation, etc., or sometimes a mere expletive): Why, it's all gone! So, 'Why, hello there' basically means 'hello', but with an added expression either of surprise, probably because you weren't expecting to meet that person, or simply extra affection towards the person you are meeting.