"moments forts" can be taken as "highlights" or "high points" so you could translate it as "These are some highlights" which makes much more sense; you might even hear that on the evening news! Et maintenant, l'actualité internationale. Voilà les moments forts.
I totally accept that this is a good French phrase or expression. It is the English translation of "These are strong moments" that is ludicrous.
"These are powerful moments." is also accepted and makes more sense.
Both @kingsley.tracy and @n6zs are wrong.
It has nothing to do with pronunciation collision.
The reason we use "ce" instead of "ces" is that "ces" is a demonstrative adjective meaning "these/those", while "ce" can be both a demonstrative pronoun meaning "they/these/those" and a demonstrative adjective meaning "this/that".
You may want to learn more about demonstrative pronouns and demonstrative adjectives.
Any time you want to write "Ces sont", just be aware that it is never written that way. To avoid a collision between the two "s" sounds, it is always changed to "Ce sont". If you hear "sont" in this context, you can be sure the preceding word is "ce". It means exactly the same thing, "These are...."
[Edit: Pardon me for posting the apparently incorrect information about colliding "s" sounds. It sounded reasonable when I first heard that. At any rate, according to Lawless, "c'est becomes ce sont when followed by a plural noun".] -31/08/15
Don't get what this is trying to say... Strong in what sense? Hard, difficult, special, great, intense...?
It is more idiomatic, I think. The literal translation of "strong moments" is ineffective. Reverso's translation in context gives "highlights" as the most common translation of "moments forts". It refers to the most memorable features or moments which are being recalled, i.e., the high points or highlights. It doesn't mean that are hard or difficult, just memorable. http://dictionnaire.reverso.net/francais-anglais/moments%20forts
It means 'difficult times' but if you say difficult in French it doesn't sound right in this context.
Not just difficult, "powerful moments" can be hard times or highlights. Those moments that stand out.
"powerful moments" is accepted.
"Powerful moments" with strong emotional ties, both hard times and highlights. "The moments of our lives"
"Ce" is an indefinite demonstrative pronoun here which can be singular or plural. "ces" is a demonstrative adjective only used to modify a noun that is plural. The confusion comes from the demonstrative masculine singular adjective which is "ce" also, but which would always precede a noun. http://french.about.com/od/grammar/a/indefinite-demonstrative-pronoun.htm http://french.about.com/od/grammar/a/adjectives_demonstrative.htm
The translation given by duo, "These are high moments" does not mean much to me in English. Reading some of the other comments suggests "These are highlights" is a better translation
If you look on Reverso, you will find that "highlights" is the most common translation of the term "des moments forts" as it is used in context. http://dictionnaire.reverso.net/francais-anglais/moments%20forts
"These are strong/powerful moments" doesn't work in English. "These are powerful times" should be allowed, especially as "times" is one of the translations given for "moments". So I'll report this!