By Karen Rosen | Aug. 02, 2017, 12:09 p.m. (ET)

LONDON -- Five years after the Olympic Games London 2012, the track and field world returns to the London Stadium in Queen Elizabeth Olympic Park. The 16th IAAF World Championships will be the third-largest sporting event on the planet with more than 2,000 athletes from 205 countries.

After the scorching temperatures in Sacramento for the USATF Outdoor Championships, where the high reached 110 degrees, the forecast for London shows highs of about 70 degrees and lows in the mid-50s.

“It’s going to be perfect,” said decathlete Trey Hardee, a two-time world champion who won the silver medal at the London Games.

We’ll see if he’s right come Friday. For now, here are some burning questions facing Team USA:

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1. Can Justin Gatlin – or anyone else – catch Usain Bolt?

The Jamaican sensation has declared that he will retire after this meet. Bolt, who will turn 31 on August 20, has dominated the international sprint scene since winning three gold medals at the Olympic Games Beijing 2008. He has won eight Olympic gold medals (actually nine, but one won in Beijing was stripped after a relay teammate’s doping suspension), and 11 gold medals and two silvers at worlds. Bolt won the 100-meter three times and the 200 and 4x100-meter four times apiece since 2009.

Justin Gatlin, 35, could be considered his top rival from the United State, but Gatlin has never beaten Bolt in a major championship. Gatlin was second to Bolt in the 100 at the last two worlds and also second in the 200 in 2015, though he won’t race that event in London.

Gatlin was the 2004 Olympic 100-meter champ, but since Bolt’s arrival, he was second last summer at the Olympic Games Rio 2016 and third in 2012 on this same London track.

Gatlin’s lone victory against Bolt in the 100 came at the Diamond League meet in Rome on June 6, 2013, when Gatlin was on a hot streak.

This season, Gatlin won the national title, edging Christian Coleman, who pressed too hard at the finish. Coleman, 21, has had a long season for the University of Tennessee, starting indoors, but he still has the top time in the world of 9.82 seconds from the NCAA meet.

Yohan Blake of Jamaica, the world champion in 2011 after Bolt false-started and the 2012 Olympic silver medalist, is next on the worlds list at 9.90, while Gatlin and Bolt are tied for No. 7 at 9.95 seconds. Gatlin ran his season best at the U.S. nationals while Bolt didn’t post his best time until July 21 in Monaco, where he had a poor start.

Andre De Grasse of Canada, the 2016 Olympic and 2015 world bronze medalist, ran a wind-aided 9.69 seconds in Stockholm this year and will likely challenge for a medal.

 

2. Will Allyson Felix hold off Shaunae Miller-Uibo for her second straight title in the 400?

In one of the most dramatic finishes of the Rio 2016 Games, Felix appeared headed for her first gold medal in the 400-meter when Shaunae Miller of the Bahamas dove across the finish line. Miller posted a personal best of 49.44 seconds while Felix’s time was 49.51. Miller’s dive proved controversial. It was perfectly legal, but internet commenters claimed Felix was robbed.

A year earlier at the 2015 worlds, Felix had a commanding lead when Miller came on strong at the end to place second.

This season, Felix, 31, has the top time in the world of 49.65 seconds on this London track on July 9, while teammate Quanera Hayes is next at 49.72. Hayes won the national title as Felix sat out the 400 at nationals.

Miller, who is now Miller-Uibo, is next at 49.77, followed by Team USA’s Phyllis Francis at 49.96, which bodes well for Team USA winning its first 4x400-meter world title since 2011. The U.S. lost to Russia in 2013 and Jamaica in 2015.

Felix is already the most decorated female athlete in U.S. track and field history. She has nine Olympic medals – six of them gold – and 13 world medals – including nine gold.

She has a happy history on this London track. Felix won the 200-meter at the London Olympics for her first individual gold after two silver medals in the event. She also ran on both wining relays.

At worlds, Felix won the 200 three straight times from 2005 to 2009. While attempting the 200/400 double in 2011, she claimed the silver in the 400 and bronze in the 200. Disaster struck in 2013 when Felix, the favorite, suffered a hamstring injury on the turn and fell to the track in pain.

 

3. Can Aries Merritt complete his comeback after a kidney transplant by medaling?

Merritt won the gold medal at the London Games in the 110-meter hurdles and then shattered the world record a month later.

Merritt stunned the world when he announced that he would undergo a kidney transplant immediately after the 2015 world championships in Beijing, but the real shocker came when he subsequently captured the bronze medal. At the time, his kidney function was less than 20 percent.

Merritt did not qualify for the 2016 Olympic team, but placed second at the 2017 nationals, the world qualifier, behind Aleec Harris and ahead of Olympian Devon Allen.

Merritt, 32, has the top time by an American this season of 13.09 seconds – which came in London on July 9 – which puts him in a tie for fourth on the world list.

Olympic champion Omar McLeod of Jamaica is the world leader at 12.90 seconds.

 

4. Does Ajee Wilson have the speed and confidence to reach the podium in the 800?

The photo showing Wilson posing next to the scoreboard in Monaco after running an American record has the name of her event, but it looks like BOOM. And it was definitely an earthshaking moment for Wilson.

Although she placed third behind two-time Olympic champion Caster Semenya of South Africa and Olympic silver medalist Francine Niyonsaba of Burundi, Wilson proved she belonged in the conversation in London. By running 1 minute 55.61 seconds, Wilson became the first American woman under 1:56. She smashed Jearl Miles’ record of 1:56.40 from 1999, and taking 2 seconds off her personal best.

But it will be tough to crack the top three in London.

Semenya hasn’t lost an 800 since she was eliminated in the semifinals of the 2015 worlds and has won every Diamond League race, usually followed by Niyonsaba or Olympic bronze medalist Margaret Wambui of Kenya.

 

5. Who will prevail among Team USA’s top rivalries?

Ryan Crouser vs. Joe Kovacs in the shot put:

Kovacs is the 2015 world champion while Crouser beat him for the Olympic title. They own the top nine marks in the world this season. Crouser won their duel at the U.S. nationals, but needed a personal best and meet record to do it, heaving 22.65 meters (74 feet, 3 3/4 inches) on his final throw.

Christian Taylor vs. Will Claye in the triple jump:

Taylor won the first of his two Olympic golds in London and again leads the world list.

Claye won silver medals in the last two Olympic Games and has two bronze medals in world championships.

Taylor has also been flirting with the world record in the event and has only lost twice since the 2015 worlds, once to Claye at the 2016 U.S. Olympic Team Trials for Track and Field and then in July to Pedro Pablo Pichardo of Cuba, who will not compete in London.

Brittney Reese vs. Tianna Bartoletta in the women’s long jump:

Reese won the Olympic title in 2012 and won three straight world titles from 2009 to 2013. She was battling injuries in 2015 and did not qualify for the final.

Bartoletta won the world title in 2015, which was an impressive 10 years after taking her first title in 2005 when she was just 19 years old. She then defeated Reese for the 2016 Olympic crown.

Bartoletta won their showdown at the U.S. nationals, but Reese leads the world list this year. She and Bartoletta have the top five jumps in the world, with Reese at 1, 2 and 5 and Bartoletta at 3 and 4.

 

6. Can the men’s 4x100-meter stop beating itself at the world championships?

Team USA has not won the gold medal in this event since 2007 in Osaka, with Tyson Gay winning his third medal of the meet. Bolt ran a leg on the silver-medal winning Jamaican team.

Due to various mishaps, Team USA failed to medal 2009, 2011 and 2015 and won the silver in 2013. The United States was also disqualified from the Olympic final in Rio.

Going back to the 2009 worlds in Berlin, no nation has gotten within 0.20 of Jamaica. The closest team was the United States in 2012 in London.

Jamaica and Team USA are tied for the record of four straight 4 x 100 titles. Team USA won in 1983, 1987, 1991 and 1993.