At 1 PM in the afternoon, take the T third to 23rd and 3rd, walk 3 blocks west then 1 block south.
Or show up at 6:15 PM and do the same thing, because the hares are stupid and decided they wanted to stand around in the rain all day, and Mr. Pump is an enabler.
Definitely no mud. It's only going to rain on people who've been naughty and deserve it. You know who you are. Come pay the piper. As a concolation, the start has a big concrete umbrella, and there will be hummus.