'Anyhow' is a discourse marker, used to indicate a change in the conversation, so it isn't like 'however':
'I'll do what you say. Anyhow, I must be going now' Here the speaker want to change the subject and uses it to signal the change. As it indicates a change, it normally comes at the beginning. 'However' can come at the beginning, middle or end of a sentence, though it is mostly found at the beginning:
However, I didn't agree.
I, however, didn't agree.
I didn't agree, however.