Ensimmäinen yritykseni
Jos aurinko paistaisi huomenna, meneeisin rannalle. Olisin menutnyt eilen, mutta (silloin) satoi (vettä).
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Good job! Using the present conditional tense (-isi) in the first sentence makes it sound quite poetic :)
More informally you could write
"Jos aurinko paistaa huomenna, menen rannalle..."
The second sentence ends a bit abruptly so I would add at least an object for the verb 'satoi'.
Unlike in English, in Finnish we typically say "sataa vettä", literally, "to rain water".