What you need to know on Wall Street today

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Residents use a truck to navigate through flood waters from Tropical Storm Harvey in Houston, Texas,

Texans on Monday morning were about halfway through the worst of Hurricane Harvey's rains, and as the storm began to return to the Gulf of Mexico, they braced for even more devastating flooding in much of the southeast section of the state.

Houston has already received more than two feet of rain, turning many roads into rivers as the city of 2.3 million people prepares for another two feet to fall in the coming days.

"This is a landmark event for Texas," Brock Long, the Federal Emergency Management Agency administrator, said. "Texas has never seen an event like this."

Here's the latest:

• Hurricane Harvey is dropping so much rain in Houston that the National Weather Service had to add more colors to its map
• Tracking Harvey: Before-and-after images show the catastrophic flooding in Houston
• Hurricane Harvey is wreaking havoc with energy markets
• 10 oil refineries in Texas have been shut down because of Hurricane Harvey
• GOLDMAN SACHS: Harvey's damage to America's oil industry could last several months
• One of the world's largest reinsurers says Hurricane Harvey will be much less damaging than Katrina and Sandy
• Home-improvement stocks are rallying after Hurricane Harvey
• Here's what you need to know if you're flying to Texas this week

In other news, Gilead announced it is acquiring the cancer-immunotherapy biotech Kite Pharma for $11.9 billion, sending biotech stocks surging. The deal amounts to a $12 billion endorsement for a revolutionary kind of cancer treatment.

On Monday, Amazon's $13.7 billion acquisition of Whole Foods formally went through, and the e-commerce giant didn't waste any time in making changes. Here's what you need to know:

• Amazon just made shopping at Whole Foods cheaper - here's exactly how much you'll save on each item
• Whole Foods is now selling the Amazon Echo
• Amazon's $13.7 billion Whole Foods buy proves the concept of the "tech company" is coming to an end
• MORGAN STANLEY: Amazon could "close the gap" between Whole Foods and its competitors' cheaper prices
• Amazon-owned Whole Foods is starting to look a lot more like Walmart

In other news, Uber has picked Expedia CEO Dara Khosrowshahi to be its new CEO. Here's what you need to know about the former investment banker.

Elsewhere, traders betting against Chipotle are making millions as avocado prices surge. GE is shifting the strategy for its $12 billion digital business. The parent company of Saks Fifth Avenue is thinking about going private. And BuzzFeed is ditching its anti-banner ad stance to better cash in on its huge audience.

Lastly, here are the 15 best business books of all time.