It was two days after Christmas. Off the Hook, a 90-foot motor yacht, had just picked up its New Year’s charter and was anchored off Marigot in St. Martin. The Christmas trades were in full effect and it was blowing like crazy. At 6 p.m., the wind reached gale-force strength and the captain put out the stern anchor as well.
The choppy anchorage was far from ideal but the guests seemed happy, cozily ensconced in the formal dining salon awaiting their meal. The chef was plating the appetizers and the stewardess was pouring the wine when all hell broke loose. Suddenly, the wind gusts reached hurricane force and every boat in the bay — which was crowded with holiday charters — struggled to hold their ground. The VHF came alive as panicked crew barked at one another, each with their own emergency.
The stewardess gave a strained smile, let the guests know she’d be right back, and scurried outside to assist the deckhand as a sailboat swung within centimeters of their starboard side. With no time to spare, the captain started the engines, ran down to cut the stern anchor, and went back to the controls as the mate lifted the bow anchor; the stew stood by with a roving fender to literally fend off loose boats, which the bay was rife with at that point.
Off the Hook moved to a better position in the bay and the captain ordered the mate to let out a heck of a lot of chain. He felt lucky that they had escaped unscathed, but mourned the loss of the stern anchor, which he knew the penny-pinching boss would be irritated about. The stewardess returned to serve dinner to the guests, who were none the wiser of the chaos that just ensued outside.
When the wind exceeds the forecast, the danger isn’t just dragging anchor, it’s everyone else around you. “That happened to us,” says Capt. David Meyer, who currently runs 100-foot M/Y Magnum Ride. “Not in this boat, but we were anchored in Miami and another boat broke loose and hit us, and the impact caused us to start dragging anchor. We were supposed to be in nothing more than about 20 knots and I think it was 35 or 40. It totally went against the forecast.”
The Caribbean in the early part of winter — as in our fictious scenario — tends to be windy as a rule. “It’s always a tricky time of year because those strong trade winds are just blowing,” says Jeremy Davis, assistant director of operations at Weather Routing Inc (WRI). These “Christmas trades” are caused by a semi-permanent ridge of high pressure in the central Atlantic that ridges down to the northeastern Caribbean, he says. “It tends to be a little stronger farther south during the winter months.”
Looking at a map of St. Martin, Davis hypothesizes what could have caused the sudden extreme winds in our scenario: “There could have been a front or a weakening front that had gone to the south of the islands. And right behind it, there was probably a really tight pressure gradient.”
If this wind comes down the mountains at the right angle, it can funnel through the valleys, which squeeze it, causing it to accelerate, he explains.
“We occasionally get reports from a lot of our clients where there is some unexpected downsloping wind, especially when they’re near islands or ports that have a lot of mountains nearby; it comes in just right and funnels right through those valleys. A good way to describe it is like a wide river that is meandering along; if it narrows, it tends to speed up.”
When the wind exceeds the forecast, the danger isn’t just dragging anchor, it’s everyone else around you.
There are a couple places in the world that are infamous for abrupt, strong winds: the Gulf of Lion in France and Gulf of Tehuantepec in Mexico. In France, the mistral blows through the Rhône Valley into the gulf. In Mexico, the Tehuantepecers are the strong northerly winds that follow a front coming through the Gulf of Mexico. “They funnel straight through that valley on the isthmus (in southern Mexico) and then spread out into the Pacific. That can produce a wall of wind with a pretty fast ramp up — all of a sudden you go from five or 10 southerly winds to northerlies at 50, 60 knots,” Davis says.
Fortunately, these large-scale wind events are predictable with good accuracy 48 to 72 hours out. It’s more of a challenge, Davis says, to forecast a very localized extreme wind effect like our worst-case scenario. “You can look at the conditions. If it is really a strong ridge, we’ll say in our forecast that abeam valleys, local areas of channeling will cause higher wind gusts than the general ambient winds,” he says. “You would have to be relatively close to the mountains for that; farther out, those winds would tend to diminish.”
As for dealing with wind at anchor, Capt. Meyer plays by the better-safe-than-sorry rule, very carefully checking the weather and choosing an anchorage for the best protection, even if it’s not a popular decision with the guests. He’s also conservative with scope. “We were just in a situation the other day when we had to anchor quickly and six-to-one would have been fine. I went three times that. The current was a good four knots, and we also had 20 knots of winds. I just wanted to make sure we stayed put, and we were fine. I saw other boats that were dragging though.”
This article originally ran in the October 2022 issue of Dockwalk.