From MW
usage: In forte we have a word derived from French that in its "strong point" sense has no entirely satisfactory pronunciation. Usage writers have denigrated \'for-"tA\ and \'for-tE\ because they reflect the influence of the Italian-derived 2forte. Their recommended pronunciation \'fort\, however, does not exactly reflect French either: the French would write the word le fort and would rhyme it with English for. So you can take your choice, knowing that someone somewhere will dislike whichever variant you choose. All are standard, however. In British English \'fo-"tA\ and \'fot\ predominate; \'for-"tA\ and \for-'tA\ are probably the most frequent pronunciations in American English.