22Jul07Motion of the Ocean
When I worked at the dive shop, I got these questions ALL THE TIME…How rough is rough? How do I know if it’s going to be rough? How likely is it to be rough? How rough does it have to be before the dive is canceled? All valid, yet difficult to answer, but let me see what I can do…
North Carolina, similar to the entire east coast…or any coast for that matter…has its issues with wind. See, the magic of an island is that, at any given point, there is a windward side and a leeward side, meaning depending on which way the wind is blowing, it’s bound to be calm enough to dive somewhere. Not the case with a coastline. In the summer, the prevailing winds in North Carolina come out of the southwest, paralleling the coast, so there is no protection at all offered by land. So, when the wind blows hard, the seas get rough.
Let me also make a distinction between “wind chop” and “swell”. Wind chop is a sea condition categorized by lots of waves, very close together that have, what the boat captains say, “no back on them”…meaning they’re like miniature ski-jumps where the boat goes up one side then comes crashing down on the other side, as opposed to gently riding over them as it would a “swell”. Wind chop can start or stop rather suddenly and is, as its name implies, completely dependent on how hard the wind is blowing. “Swell”, on the other hand, refers to big, wide rollers that have a lot of space in between them. Swell is generally caused by offshore storms and doesn’t fluctuate as quickly as chop. While swell can have an impact on visibility and current, it’s typically not a problem for topside conditions unless compounded by wind chop. In other words, a 4 foot swell is not an issue, but a 4 foot chop can be downright uncomfortable. And, the two together? Forget about it.
So how rough IS “rough”? Your perception will vary according to what you’re used to, but here are some guidelines. 1-2 foot seas produce calm, lake-like conditions. 2-3 foot seas make for a pretty good day on the water, though it is a tad bumpy. A solid 3 foot is doable not miserable, where 4 foot is doable but definitely miserable. 5 foot is no fun at all and if you are in 5 foot seas, you’re probably on your way back to the dock. Anything 6 foot or over, if you left the dock at all (which is unlikely), there is no chance you’re getting in the water. The most common is a 2-3 foot sea, which comprises about 60% of all diveable days. The remaining 40% is evenly split between the marginally miserable, miserable, and absolute perfection. A good rule of thumb- the actual size of a wave is two-thirds the size you think it is. What you think are 3s are really 2s, 6s are 4s, 8s are 5s, etc. (This caveat is included to save you the embarrassment of claiming you went diving in 8 foot seas to those who know better. And I promise you, as you’re reading this there are absolutely folks saying out loud to themselves or to those around them, “Pfffft. I was too out in 8 foot seas!!”)
But, what winds produce what seas, you ask? Out of the southwest, winds exceeding 15 knots will create sea conditions that over a few hours, build to the point of being undiveable, If you’re reading NOAA’s marine forecast, and you see words like “light and variable” or “winds 5 to 10 knots”, you’re in for a fabulous, “dead slick calm” day on the water. Another common forecast is “SW winds 10-15 knots”, which is a lot like a “50% chance of rain” in that it sounds like you’re being provided with information, but actually, you know nothing. When you start to see “SW winds 15-20 knots”, your chances of visiting the Aquarium are rising, though if the boat departs early enough, you might be OK. Anything over 20 knots, go to breakfast, then buy a kite. And, while you’re sure to be disappointed, I promise you that you’ll be infinitely happier on land than you would be on a boat. In fact, and I will leave you with these final words of wisdom: It is always better to be on land wishing you were out there than it is to be out there wishing you were on land.
What are the best months of the year to dive in NC? Do you do trips outside of NC or US as well?
Hi Fred- good question. The best time to dive in NC is mid-June through mid-August. Water and air temperatures are the warmest, visibility is usually the best, and the seas are generally calmer. That being said, May and October are beautiful- less crowded, not as hot, and vis is still pretty good. Hope that helps! -Lauren
October 2nd, 2007 at 9:43 pm