San Diego will be warm to very warm in March and you can normally expect sea conditions to be fine then. It will become warmer as you approach Hawaii. We did this trip in reverse and up to Vancouver in April and encountered no problems with the sea conditions going even that far north. Hawaii, as you know, is a State of the USA and as such has a very similar economy to the mainland, a few things are cheaper and some more expensive but in the main very much the same. Regards. ... Neil.