I’ve covered Manhattanhenge many times on this blog in the past. You can search the blog to find out the scientific detail but essentially it is the dates where the rising or setting sun perfectly aligns with the cross streets of Manhattan. Tomorrow is a rising sun date so set your alarm to be able to get up early enough to get to a cross street (14th Street is a good choice) so you can snap a pretty picture. Weather should cooperate with a few clouds perhaps.
If you want to experience it for yourself, check out May 28 and July 13, 2021 for sunset versions which don’t require an early wake-up call. Even if weather is iffy, the day on either side can often work out. So make some travel plans as hopefully the pandemic will be fading in New York and the sun doesn’t wear a mask.