Apologies … I noticed later, in another thread, that you were Irish.
… you know, I don’t think it (the stressed final AY pronunciation mentioned in the OP) really came from anywhere. Not a traceable “place”, anyway. The best we can probably do is point out the different linguistic influences affecting the speech communities of North America vis a vis those in Ireland/Great Britain.
One untested theory of mine is that when words entered British/Irish English first, and then entered American English later, they come into American English primarily via print (as opposed to speech). That will get in the way of British/Irish pronunciations having an early influence on the way Americans will adopt a word phonetically. This would have been even more true in the days before widespread television broadcasts.
Disagree strongly. The [for-TAY] pronunciation is now standard. Again, from the Oxford Dictionary’s online site, World English option selected (so that American definitions and pronunciations are excluded):
The pronunciations are given descriptively. The one you’re saying is “incorrect” is given as the primary, most common pronuncuation as the word is used today. Notice that it’s rendered in a British dialect (['fɔːteɪ] instead of the American [fɔr’teɪ]); conveying that even in Britain, one-syllable [fɔːt] is now a minority variant.
How are you defining convention? If I pronounced forte as in French, everyone would think I was mispronouncing it. Seems to me that that pretty much establishes the convention that the Italianate pronunciation is the correct one.
ThelmaLou, I noticed you wrote that your father is Texan. Since you’re American, you may reject my post above as mere Britishisms, and that in America forte sounds like fort. But even using Oxford’s American English option:
The /fôrt/ pronunciation given is still a recognized standard variant. But /ˈfôrˌtā/ has taken over in terms of numbers of speakers. It’s not right or wrong … languages just change that way. A Northumbrian from AD 800 might well chide us modern speakers for mispronouncing horse – he’d be telling us it’s supposed to be /hrɔːs/, with the “r” preceding the “o”!