By Amanda Delaney
Most sailors and cruisers are making their progress to the Caribbean Sea or have settled into their destination by winter. It’s time to enjoy the trade breezes and warm air temperatures. Then, occasionally, Mother Nature decides to remind everyone that it is indeed winter when large northerly swells barrel down from the northwest Atlantic Ocean to the northeastern Caribbean Sea.
Be aware of signs in the weather over the western Atlantic Ocean that indicate when these large northerly swells will develop and head toward the Caribbean Sea. These factors may give you a heads up to reposition your vessel to a more sheltered location from the north and northwest.
Localized seas versus swells
Just to clarify the type of waves that we are discussing here, wind-driven seas are more localized and wind based. This means that they usually come from the same direction as the wind and are generally shorter in duration.
A swell is a wave formed when winds from a distant gale or strong highpressure system blow steadily across a wide stretch of ocean, sometimes 1,000 to 2,000 nautical miles away. The swell is generally larger, but waves coming from so great a distance usually arrive as longer period rollers of approximately eight seconds or more.
Why does this usually occur in the winter?
The northerly swells can develop at any time of the year. They usually occur when a strong low or tropical cyclone develops to the north of the northeastern Caribbean. During the winter months (December through March), the Atlantic gale/storm track is the most active, strongest, and farthest south. Therefore, these systems are more likely to produce these larger swells due to their proximity and strength in winter towards the northeastern Caribbean
Why does this happen periodically over the northeastern Caribbean?
Not every gale or storm tracking over the western Atlantic generates large north to northwest swells that will reach the northeastern Caribbean. Most of the time, the gales or storms move too quickly across the northwestern Atlantic, or these systems do not strengthen until over the central North Atlantic. Therefore, the larger swell remains to the north and east of the Eastern Caribbean.
However, several developing factors may allow the larger swell to build from the storm and reach the Northeastern Caribbean. These include:
- Gales or storms that generally develop south of the Canadian Maritimes or along cold fronts farther south between Bermuda and the northeastern Caribbean Sea, and just east of this region.
- Strong high-pressure systems that block the gale or storm’s progress and keep it over the western Atlantic Ocean for 2–3 days longer than normal.
- Rapid strengthening of low pressure, intensifying from a gale into a storm within 1–2 days.
When these rapidly developing storms sit over the northwestern Atlantic, this allows time for the large swell to propagate from the storm down toward the Northeastern Caribbean.
Sometimes, when a gale/storm develops over the central North Atlantic, a strong high will build over the western Atlantic Ocean. If the gale/storm remains in place, the interaction between these two weather features can generate gale-force northerly winds that will generate large northerly swell that will spread toward the northeastern Caribbean Sea.
How long do the large swells last over the northeast Caribbean?
This depends on how long the gale/storm remains over the northwestern Atlantic but, at times, the swell will last two to three days, and in more significant events (or if there are multiple gales/storms to the north) these events can last as long as a week.
How to avoid the northerly swell
As always, it is good to remain vigilant on the latest weather patterns, not only for just the Caribbean Sea but also for the western Atlantic Ocean as well. If you use a weather app or another online weather source, be sure to view not just the Caribbean Sea but the western Atlantic Ocean to see the gales/storms forming offshore the US East Coast and potentially the large swell building down towards the northern Caribbean Sea. A weather provider can also give you detailed information on when exactly the large swell will reach the area you will be traveling in, so you know exactly when you’ll need to arrive into a port/sheltered location ahead of time.
Research your protected anchorages ahead of time in the area you will be traveling in. When you start to notice the swell building on your weather charts/app, then it is time to head to your protected anchorage to stay ahead of the rough swells.
Caribbean Compass contributor Amanda Delaney is a senior meteorologist with
