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".