It rained all/right through June and into the first half of July.
Could anyone please explain me about the use of into here?
What does it mean by using into?
Can you use something else instead?
The writer is contrasting "all through" or "right through" with "into", meaning "part-way".
So the sentence is saying that it rained during the entire month of June and continued raining during the first part (though less than half) of July.
The sentence means it began raining in May, continued raining for all of June, and stopped before the middle of July.
Similar to how "at", "on" and "in" can be used to describe the moment something happened, like, "at noon", "on Sunday", "in July", the preposition "into" can be used to describe an action starting in one time period (June) and moving into another time period (July). So "into" is a preposition of movement, both for physical things through space, and actions through time.