New Orleans faces the potential for one of its worst flood events in history this weekend, Axios Science Editor Andrew Freedman reports.

The big picture: Tropical Storm Barry is lumbering off the coast, pulling copious amounts of moisture from the warm waters of the Gulf of Mexico and poised to direct it like a firehose at Louisiana and Mississippi.

• The National Weather Service has issued a rare "High Risk" excessive rainfall outlook for coastal Louisiana, including New Orleans, three days in advance.
• This is only the 3rd use of this warning since 2007. (Hurricanes Florence and Harvey were the other 2.)

Why it matters: The Mississippi River is already so high in the New Orleans area that heavy rain plus a storm surge could overtop the cities' river levees for the first time, flooding parts of the city.

• Up to 2 feet of rain is likely to fall in parts of Louisiana as the storm wanders onshore like a car inching forward at rush hour. This rain could overwhelm New Orleans' pumping systems, causing a repeat of Wednesday morning's flash flood emergency.
• The rain, combined with a storm surge of 3–5 feet from the incoming storm, could cause the Mississippi River to rise between to 19 or 20 feet in New Orleans.
• The river levees protecting the city are 20 feet high and haven't been tested in this way. (Hurricane Katrina in 2005 caused failures in the city's storm surge protection system.)

The bottom line: Residents of New Orleans, and indeed much of the central Gulf Coast, need to prepare now for a significant, dangerous storm.

• The threat of deadly flooding will extend well inland into Louisiana, Arkansas, and Mississippi through the weekend and into early next week.

Harvey Weinstein exits after his appearance in criminal court on sexual assault charges in New York City.

• Weinstein is facing rape and sexual assault charges from two separate incidents.

1. Twitter was hit with a major outage, going offline this afternoon.
2. UN inspectors have reportedly found evidence of illicit nuclear activity in an Iranian warehouse, four Israeli officials told Barak Ravid of Israel's Channel 13 News.
3. House Democrats have voted to subpoena 12 Mueller witnesses with ties to the Trump administration, as well as officials involved with child separation at the U.S. border.
4. Former House Speaker Paul Ryan viewed retirement as an "escape hatch" from two more years working under President Trump, according to Tim Alberta's new book "American Carnage," per an early copy obtained by the Washington Post.

Good news: "Koko the chimpanzee, once a star in Skopje’s zoo, has returned home after spending 10 years in the Netherlands recovering from depression," the AP reports.

• "Koko was reunited with his keeper, Dragan Trajkovski, ... who said he was overjoyed to see the chimp again."
• “'It was a joy I cannot describe,' the 49-year-old told The Associated Press. 'After 10 years, Koko recognized me. We touched each other, he turned his back for a little scratching and pursed his mouth in a chimp kiss.'"