Have you ever seen a map like this? It is called a Pilot Chart, and is my favorite out of all the paper charts on board: it tells you, for each month of the year, the average prevailing wind direction, wind strength and current for any spot in the ocean, based on 100+ years of ships’ logs.
A sailboat cannot sail directly into the wind; the best you can do is dogleg back and forth at a 50-60 degree angle (called “tacking”), which is slow-going and a rough ride. It is far more pleasant to go where the winds will take you, and Pilot Charts are their best predictor more than a week or two out.
You are looking at the April chart for the Gulf of Mexico, Caribbean, and Bahamas. Take a look to the east of Jupiter, FL, at the blue wind rose with what looks like arrows stuck into it. There are eight arrows for each of the eight standard directions (North, South, Southeast, etc.), and the length of the arrow shows the relative percentage with which the wind blows from that point on the compass. Here it appears that the wind almost always blows from the East, Northeast, or Southeast. So if you are trying to go East, as we are, this would not be the ideal place to do it. It’s not a deal breaker, however: westerly winds are infrequent, but do happen in the wake of cold fronts, when the wind clocks around predictably and sometimes creates a window to make easting.
Back to the arrows. The number of feathers denotes the wind speed / sea state using the Beaufort Scale
(1 for dead calm, 12 for a hurricane). Force 4, as shown here, is decent sailing: 11-16 knots of wind and smallish waves, pretty typical conditions in these latitudes. We mustn’t forget, however, that half of the sample size was higher than this average level, and also that ships try to avoid areas where the weather is bad, so there are fewer reports of bad conditions than there would be, were this not the case.
Notice the fat green arrows flowing up the Florida coast – that is the Gulf Stream, a massive river of warm water that gushes through the Florida Straits and up the East Coast. The contrast between the Gulf Stream’s warmth and the colder surrounding waters causes much mischief for sailors in the North Atlantic, stirring up Noreasters and other nastiness all the way to Iceland. Down here, though, it bestows wonderful warm temperatures all year round!
The Gulf Stream moves fast by ocean current standards – 3.0 knots at its middle, fastest point – and it is 40-50 miles wide, so one must account for drift when plotting a course across it. The most efficient means of doing so is to steer a single compass heading the whole time, crabbing into the current, which, if properly calculated, will produce an S-shaped course that terminates at your desired port of call. If the winds have been calm and south of East for a few days, the sea state in the Gulf Stream should be safe for a crossing. If out of the North, however, forget about it: contrary winds fighting against the Gulf Stream create tall, short period waves that can capsize a small boat like ours.
These charts are particularly useful when deciding where to sail, and when. For instance, we haven’t decided where we will go after the Bahamas. It would be nice to sail to the Windward & Leeward Islands of the Eastern Caribbean, but the Tradewinds would be in our face the whole time – and get stronger the further into summer we go. Sailing to Cuba or Jamaica, on the other hand, would put the wind at our backs – definitely an easier way to go! Exploring the SW Caribbean also puts us near the Panama Canal, which we’ll need to traverse to reach our ultimate goal, the Pacific. But we are getting ahead of ourselves.
This set of Pilot Charts was created in 2002, and one might wonder whether climate change hasn’t wrought material variances to these observations. My own limited comparison of these figures against a more recent set (Cornell’s Ocean Atlas) did not yield much of a difference: wind in the Bahamas still comes from the East, perhaps a few percentage points more often than before, but no significant pattern of change. So what if there are east winds 53% of the time, instead of 47%? These are prevailing i.e. normal conditions and do not preclude the possibility that there are more and bigger extreme weather events being driven by our planet’s warming.
There is a lot more information on these Pilot Charts than I have covered here, like gale frequency, temperature, sea ice / icebergs, and much more. They are free to look at online – have a look and you are guaranteed to learn something new!