can someone please enlighten me on this. It’s mainly an americanism right?
Found this lol Im an American and never really heard of it myself.
Must be slang for like Yikes! I dunno 
Well, if the TV show Friends has taught me anything, it’s that “Yowser” is an expression of surprise, or when something unexpected happens.
I always thought of it as a British exclamation. Like, “Yowsah!”
Hmm, I’ve never heard anyone in the UK say it!
lmao lol
Hey i learn something new everyday! 
It would be more similar to “Wow, that’s surprising and unexpected!” It’s an expression of mild shock and disbelief.
Isn’t youwsa == “yes, sir!” ?
Yowser was a phrase used by a cartoon detective named Inspector Gadget during the 90’s. It’s a excited exclamation phrase.
"Yowser, All my HTML pages are gone! "
Hmmm… I couldn’t find any connection to “yowser” and Inspector Gadget on Google. A couple of the other ideas also sound fairly convincing, the Zappa reference, that sounds like it.
Yowser was used a lot in Inspector Gadget.
Basically yes it is “Wow, how unexpected, and possibly shocking to me.”