Incorrect on both counts. 追う ou "to chase" is a simple example of separately pronounced consecutive vowels.
港南, on the other hand, does not have a "u" sound of any kind, it's simply a long "ō", which doesn't really exist in English. The reason it's occasionally spelled with a "u" (although not in any formal standard) is because hiragana uses the letter う to indicate long o and u.
My point was that you do not pronounce that word as "oh u". There's no glottal stop, nor are the vowels "separated". But I agree it's not a familiar concept to English speakers, nor is it easily expressed in romaji. If I were explaining it to a native English speaker who didn't know Japanese at all, I'd tell them to say "owe"...but that's not hepburn.
> 港南, on the other hand, does not have a "u" sound of any kind, it's simply a long "ō", which doesn't really exist in English.
Yes, that was exactly my point. It's a long vowel. The closest approximation in English is not "ko", but "kou".
I disagree that this isn't in English, however. It's an easy concept to map -- we have tons of repeated vowels -- which is why "kounan" gets the pronunciation pretty close.
Directly addressing the question I was responding to, there's no question about "ko un an" vs. "kou nan", because the former requires you to stop the airflow between the "ko" and "un" in a way that isn't natural for Japanese. Knowing that consecutive vowels will essentially always "smoosh together" allows you to pronounce the word -- so long as you know the vowel is long.
港南, on the other hand, does not have a "u" sound of any kind, it's simply a long "ō", which doesn't really exist in English. The reason it's occasionally spelled with a "u" (although not in any formal standard) is because hiragana uses the letter う to indicate long o and u.