Here's the filled-in dialogue:
Alex: Hey, Jamie! Do you have any plans for this weekend? Jamie: Not yet. (1) I am thinking about going hiking. What about you? Alex: (2) That sounds fun! I will join you if the weather is nice. Jamie: Great! (3) But I won't go if it rains. Alex: I understand. I'm going to check the weather forecast later today. Jamie: Good idea! If it's sunny, we can leave early in the morning. Alex: Perfect! Jamie: I can't wait! Bye. (d) See you soon.