De moins en moins de means less and less or, with countable nouns in natural English, often fewer and fewer.
So:
This expression shows a gradual decrease over time.
Compare:
This is the normal structure.
The full pattern is:
Examples:
The first de is part of the whole quantity expression, and the second de introduces the noun that is being counted or measured.
After expressions of quantity or comparison, French usually uses de, not des.
So you get:
You would not normally say de moins en moins des feuilles here.
Because feuilles is a countable noun: you can count leaves.
In careful English:
So the most natural translation is:
But French uses moins for both less and fewer, depending on context.
The comma separates the introductory time phrase from the rest of the sentence.
This is similar to English:
The comma is natural because En novembre has been moved to the front for emphasis or clarity. In short sentences, punctuation can sometimes vary, but this comma is completely normal.
Yes. That would also be correct, but the meaning changes slightly.
The second version emphasizes a continuing decline, as if the number keeps dropping over time. That makes it especially suitable for autumn.