John Gill Commentary 1 Kings 18:1

"And it came to pass after many days, that the word of Jehovah came to Elijah, in the third year, saying, Go, show thyself unto Ahab; and I will send rain upon the earth." — 1 Kings 18:1 (ASV)

And it came to pass after many days
When two years and more were gone from the time the drought and famine began; or rather from the time of the prophets departure to the brook Cherith, which might be six months after the famine began:

that the word of the Lord came to Elijah in the third year ;
of his absence from Ahab:

saying, go show thyself unto Ahab ;
whom he had not seen so long, and who had been seeking for him, but to no purpose:

and I will send rain upon the earth ;
the term of three years and six months being almost expired, see (James 5:17) .