A high crude oil spot price wipes out oil contango, which is bad for tankers. So if the oil spot price gets a breakout and a close above $20, that will the signal to sell tankers (perhaps even to buy puts on NAT). Personally I think it's more likely that WTI gets rejected from the $20 level and falls back below the 20-day EMA. That will be the signal for another leg up in tanker stocks.
There are three factors that might hurt tanker demand and reduce booking fees: 1) If oil prices strengthen and there's less demand for storage, 2) if storage fills up, or 3) if producers cut production. The odds of one of these things happening sometime soon are pretty high. And if producers cut production *for good* (e.g. the whole US shale sector goes out of business), then the effect on tanker fees will be long-term. So there's definitely risk here.
But still, this dividend is extremely high, and it's at no imminent risk of being cut, so I do think there's an opportunity here that a lot of people are missing.
Here's the latest: https://seekingalpha.com/news/3556283-oil-tanker-rates-keep-surging-amid-one-of-greatest-quarters-in-history