Weather in croatia around september can get a bit chilly indeed, last year it only rained from sundaynight till tuesday (so the festival was over allready, we were lucky i guess). But on the boats at night u better get a sweater on. Although in the fort it's way too hot, with all the ppl aroudn you and u probably getting more drunk every hour, u'll never get cold without a sweater in the fort at night.
Even in the morning it wasnt really chilly and the sunrise is wonderfull!
Was us leaving the fort going down that small road and the sun just rising above that hill.
And as u can see, around 3 oclock at night, almost no one wearing sweaters :
Concerning illegal substances, beware, i advise to not bring anything along too croatia.. Croatia is not yet part of the eu so they will search you when you enter the country, wether it is by bus, car or plane. We almost got searched last year but we didnt had anything along, although we we're scared, we showed really confident, they believed us and just let us pass along, but i dont think everyone would be that lucky.
At the festival self there is plenty too find, last year before i went too outlook i got to know a guy in croatia, we became friends and he provided us with the greens too.. It wasnt that good of stuff but it was allright to smoke and we were happy to smoke our spliffs at the fort, boat and beach.
You just have to be carefull for the undercover cops, but they are so out of bound that u recognize them immediately and if u spot one, just make sure they dont see u do any drugs. Otherwise they will search you and you'll end up paying a big fine or even wind up in jail.