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KNOW IT ALL: Monday's Top Stories at NBC News

From grounded flights to Olympics highlights, here are the stories we're following today.
Image: Swimming - Women's 400m Freestyle Final
American swimmer Katie Ledecky wins gold in the 400-meter freestyle, breaking her own world record by nearly two seconds.Michael Dalder / Reuters

Good morning. Here are some of the stories we're following today:

1. Delta Computer System Outage Grounds Flights Worldwide

Tens of thousands of Delta passengers around the world were grounded Monday due to a system-wide computer failure, with the airline unable to say when the problem will be fixed. "Our systems are down everywhere," the airline told customers on Twitter. Read more in NEWS.

2. Dozens Killed in Attack Targeting Pakistan Hospital

A powerful bomb went off on the grounds of a hospital in the southwestern Pakistani city of Quetta on Monday, killing at least 52 people. Television footage from the site showed scenes of chaos, with panicked mourners fleeing through debris as smoke filled the corridors of the emergency ward. Read more in NEWS.

3. Japan's Emperor Hints at Handover in Rare Address

Japan's Emperor Akihito broke his silence Monday in a rare television address in which he addressed abdication rumors and expressed fears about his ability to fulfill his duties due to his advancing age. The 82-year-old said he was "in good health" but was "worried that it may become difficult for me to carry out my duties as the symbol of the state with my whole being as I have done until now." Read more in NEWS.

4. Highlights from Day 2 of the Rio Olympics

Michael Phelps won his 19th career gold and 23rd medal overall, as Team USA brought the 4x100m freestyle relay title back to American soil after a bitter taste from silver in 2012. Katie Ledecky smashed her own world record by nearly two seconds in the 400m freestyle to win her first individual gold of the Games to go along with her silver from the women's 4x100m freestyle relay. Read more in SPORTS.

5. Boy Killed in Accident on World's Tallest Waterslide

A 10-year-old boy was killed Sunday in an accident at Schlitterbahn Water Park in Kansas City, Kansas, police and the park said. Winter Prosapio, a spokeswoman for the park, said the boy died on the Verrückt, which is billed as the world's tallest waterslide. Read more in NEWS.

6. U.S. Professor, Colleague Kidnapped in Kabul

An American professor and his Australian colleague have been kidnapped in Afghanistan's capital, an official at their university told NBC News. The pair were snatched as they sat in their car Sunday night following classes at the American University of Afghanistan in Kabul. They have not been named publicly on the request of authorities. Read more in NEWS.

7. Storm System Expected to Swamp, Steam Gulf Coast

State officials urged residents and businesses Sunday to prepare for heavy rain leading to widespread flash floods this week along the entire width of the Florida Panhandle. A low-pressure system was stalled over the northern Florida peninsula, fueling a chance of heavy showers and thunderstorms that the National Weather Service put at 80 percent to 90 percent across the northern Gulf Coast. Read more in WEATHER.

8. Three Kids Among Family Killed in Murder-Suicide

A family of five, including three small children, was found dead in their Pennsylvania home Saturday along with what authorities described as a handwritten "murder-suicide note" grappled with a child's illness, post-traumatic stress and strife in their home in recent years. Read more at NBC PHILADELPHIA.