News

Caribbean Cruising Weather: What’s in Store

5 February 2009By Chris Tibbs

With winter storms battering northwest Europe and bitter cold gripping the northern U.S., it’s not surprising that the Caribbean is a popular cruising area right now. Currently, we are in the more settled season for Caribbean weather, which runs from December thru May.


Trade winds

At this time of year, the trade winds blow with a great deal of regularity from the ESE to NE, at a Force 4 on the Beaufort scale, which is 11 to16 knots. This is an average at 10 meters, so instruments on board will be measuring closer to 15 to 20 knots. Averages do not take into account where the wind is modified by the islands, or where there is shelter in their lee.

This steady wind direction is recorded for around 90 percent of the time in the southern Caribbean islands, but is more variable to the north (particularly north of the Virgin Islands), as depressions in the North Atlantic exert more influence. Florida and The Bahamas are likely to experience spells of typical trade winds, broken by cold fronts from the States crossing the area. These can be intense during mid-winter, and may reach as far south as the Virgin Islands, but are usually short-lived.

The end of December thru January sees a period of stronger wind known as the Christmas trades. Once the trade winds are established, they are likely to remain reasonably strong.

Driving the trade winds is the position and intensity of the Azores (Bermudan) High. This varies throughout the season and also year to year. When the Azores High is in position the trades will blow with great regularity. If the high is split by a cold front moving south, the trades will weaken and fail in the northerly islands.

The seasonal forecast for this year is for average to slightly above-average Caribbean trade winds. There is also a link between an El Ninõ event in the Pacific and stronger-than-average trade winds in the Atlantic. Currently, we have a weak La Niña (slightly below-average seawater temperatures in the central Pacific), which is expected to continue for the next few months. This indicates slightly below-average trade winds in the Atlantic.

These two slightly contradictorily indicators imply that we should not have an exceptional year in one way or the other. Day to day, there will be variations, but the seasonal average should be close to normal.


Rainfall

Out at sea, rainfall is almost all from large squall clouds. The number and intensity of squalls will depend on conditions in the upper atmosphere and the instability of the atmosphere. As a rule, large raining clouds will give intense squalls with winds of 30 to 40 knots. However, these will sometimes become more intense if the atmosphere is particularly unstable and squalls of 60 knots are possible. Not only is this increase in wind of concern, but it will be accompanied by a significant decrease in visibility due to the heavy rain.

Near islands, the topography of the land dictates the amount of rainfall. Although the Caribbean rainy season does not start until May, the higher islands will often have cloud cover. We do occasionally get large areas of rain and squalls working their way north from the ITCZ (Intertropical Convergence Zone), affecting the southern islands with bands of cloud and rain.

Most of the time, the weather will be good, but out of season storms are possible. Weather forecasts should still be monitored, as it is easy to get a false sense of security after an extended period of steady trade winds. A drop in pressure and greater than the normal diurnal rise and fall are also indicators of unseasonabe weather ahead.

Chris Tibbs is a meteorologist who previously worked as a skipper in the yachting industry. He is the author of the Onboard Weather Handbook (McGraw-Hill).

What’s your take on the Caribbean weather this year? Normal or nasty?