One of this year's more surprising winners is SeaWorld Entertainment (NYSE:SEAS). Shares of the theme-park operator stock have soared 116% in 2018 through Thursday's close, landing new recent highs this week.

Things aren't perfect. The big ride that was supposed to drench guests at its busiest park has yet to open, missing the peak summertime travel window. PETA and other activist groups are still stirring the Blackfish pot. However, SeaWorld shares are hitting four-year highs, so it must be doing plenty of things right. Let's size up the reasons behind the killer rally in the killer whale stock.

Manta coaster at SeaWorld Orlando.

Image source: SeaWorld Entertainment.

1. Attendance is surging again

The market was impressed with SeaWorld's blowout first quarter in May, but the 16.5% surge in revenue wasn't much of a surprise to watchers of the holiday calendar. SeaWorld was coming off of depressed results a year earlier as the Easter holiday -- a peak time given the schools that time their spring breaks around that time -- slipped into the second quarter in 2017. That tailwind should've been a headwind during the second quarter of this year, but SeaWorld impressed the market again with a robust financial report this summer. 

Revenue rose 4.9% during this year's second quarter as turnstile clicks increased and folks continue to spend more once inside a SeaWorld theme park. Revenue through the first half of 2018 is up a hearty 8.7%, a big deal since eyeing the entire first half of the year smooths out the Easter holiday timing fluctuations. 

2. A new CEO can work wonders

Joel Manby seemed to check off all of the boxes when he arrived as CEO three years ago. He came from the critically praised theme-park operator behind Dollywood and Silver Dollar City. He was a star on Undercover Boss. He had written a management book emphasizing that love for employees is the key to effective leadership. 

It didn't pan out. He was too eager to provide concessions to the activist groups that angered SeaWorld regulars without fully appeasing the detractors. He bowed out in February, and SeaWorld's chief parks operation officer -- John T. Reilly -- was appointed interim CEO. It will be hard to remove Reilly from the post given the stock's sensational run since he took over in late February. 

Reilly is a SeaWorld lifer, and while an outsider was the right call when the Blackfish controversy was bubbling at the time of Manby's arrival, it's now time to keep the turnaround in place, going from the perspective of someone who has been working there since he was selling soft drinks at Busch Gardens Williamsburg when he was 16. 

Reilly has set the lofty goal for SeaWorld to hit $475 million to $500 million in annual adjusted EBITDA by the end of 2020, well above the $300.8 million it scored in 2017. His plan to keep adding new rides and attractions while controlling costs is the right approach at this time. 

3. Starting lines matter

SeaWorld hasn't traded this high since the months following its 2013 IPO. It is finally back above its $27 IPO price. More importantly, it ended 2017 trading in the low teens. The stock had bottomed out last November as hurricanes -- Harvey in Texas and Irma in Florida -- rocked SeaWorld parks during the third quarter of last year. 

Comparisons will obviously be easier this time around for the current quarter, but SeaWorld wouldn't double this year if it wasn't depressed when the year began. Sometimes a monster gain is all about timing. 

Rick Munarriz has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.