Monsoon season, changing the trade winds that would have taken them south, ultimately ending up in Antarctica.

ARZT: It's been raining every damn afternoon. That means that we are on the cusp on monsoon season. Monsoon season is bad. Now, the trade winds are blowing north right now -- shipping lanes are north -- so north is exactly where you want to be.
MICHAEL: What does that mean?
ARZT: It means that when monsoon season hits the trade winds are going to shift to the south. The raft goes with the wind. Can anyone tell me what is the only piece of land that is south of us?


Source: Lostpedia

__________________
Please don't give up, Des. Because all we really need to survive is one person who truly loves us. And you have her. I will wait for
you. Always. I love you, Pen

DESMOND: I love you, Penny. I've always loved you. I'm so sorry. I love you!
PENNY: I love you too.
DESMOND: I don't know where I am, but--
PENNY: I'll find you, Des--
DESMOND: --I promise--
PENNY: --no matter what--
DESMOND: --I'll come back to you--
PENNY: --I won't give up--
BOTH: I promise. I love you.