[noun] + とあって [na-adj] + とあって [verb (plain)] + とあって [i-adj] + とあって
とあって gives a special circumstance as the reason for what follows: "since it's…", "as it was…". The circumstance is out of the ordinary – a holiday, a first time, a famous name – and the main clause is what you would expect to happen because of it. A noun or a な-adjective takes とあって directly; a verb or an い-adjective is in the plain form.
The main clause describes a situation you can observe: crowds, sold-out tickets, someone's mood. It is not the speaker's own decision, request or plan. An everyday reason does not take とあって either.
とあって belongs to news reports and written narration. In conversation the same reason takes から or ので.