When do you plan to go? It's peak rainy season in Central Vietnam now through Nov. Friends report Hoi An is fine at the moment (just the normal, seasonal rains) but this time last year, Danang had 1.5 meter floods. HCMC's had a heavier than usual deluge of late, but nothing that would affect a trip there significantly, especially if staying at any of city's Marriotts which are mostly located (quite close together) in the District 1 downtown core.