There's a pun for the promotion name, "Swell Deals".
Any waves higher than 21 feet get you 30% off, ranging down to 10% off for any waves less than 10 feet. The discount applies for flights booked until Friday November 8, 2019. You must travel by November 20, 2019.
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To take advantage of the of the deal you have to enter the code "SURFLINE15" in all caps at checkout.