How can I start a sentence with however
and hopefully
?
(In terms of semantic, grammar and punctuation)
A typhoon is looming. However hopefully, we are leaving the city.
A typhoon is looming. However, hopefully we are leaving the city.
You need a comma after however: it's an adverbial that makes a meaning connection between sentences and cuases a short pause. Using a comma after hopefully is less common:
hopefully the road should be finished by next year
Source: Oxford Dictionaries.
Also here's a search in Google Books. As you see in most cases hopefully isn't followed by a comma.
A typhoon is looming. However hopefully, we are leaving the city.
However, hopefully, we'll be leaving the city.
Please bear in mind: hopefully and to hope are not the same thing. Hopefully is used to replace it is hoped in contemporary spoken English but if you think about it, you will see that it does not actually mean: A typhoon is looming. However, we're hoping to leave the city.
In any case, hopefully here would call for a will future. Hopefully indicates intention, not an actual fact. Hopefully is incorrectly used here if you like or adhere to formal grammar rules. Otherwise, it's OK.