Voyager experiences strange pacific current
Recently, when sailing in the Pacific, we experienced an unusual current that didn't fit with the standard model of how the currents in the central Pacific should work. We were sailing from Nuku Hiva in the Marquesas to Hawaii on board our 45-foot steel ketch Havaiki. The North and South Pacific Equatorial currents and the Pacific Equatorial Countercurrent usually move slowly but steadily as depicted on the pilot charts. The Southern Equatorial Current usually begins just north of the equator itself, flowing generally westward at a nominal speed of one knot. The northern limit fluctuates depending on the time of the year. The flow can meander northerly or southerly somewhat, and, is usually strongest between its northern limit and about 5° south latitude.
The Northern Equatorial Current begins around 10° north latitude and also moves generally westward, but with less force than the one to the south, usually about 0.8 knots. Again, it can vary in its flow either with a northerly or southerly component, and its southerly limit varies also with the time of the year. The Northern Equatorial Current usually ends around 20° north as it is affected by the North Pacific Highs.
Separating these two currents is the Equatorial Countercurrent, which flows normally in an easterly direction at a nominal rate of one-knot, varying in flow with the time of the year. Once again, the countercurrent can also have a northerly or southerly component. The counter current does not cross the entire Pacific Ocean. It usually begins around 90° west longitude and ends somewhere around the dateline. The northern and southern limits as well as the area it covers also vary with the time of the year, and they tend to lie in the area of the inter-tropical convergence zone (ITCZ) which most sailors refer to as the doldrums.
The countercurrent gets closer to the equator the farther west you go, and the farthest north usually around 135° to 145° west longitude. It is this countercurrent that sailing ships would search for to help them get their necessary easting in days before engines, and even today, yachts that have only limited fuel supplies search for it and use it to their advantage.
For the most part, these rivers of water in the ocean are quite dependable, although on our trip from Hawaii to Samoa last year we had an easterly setting current all the way south until we picked up the South Equatorial Current, but everything was back to normal by the time we headed back north in November.
This year was different, however, and although the effects were quite welcome, they were strange and so far unexplainable. This year I made my seventh and eighth crossing of the equator. The track of this latest trip on our way back to Hawaii from Tahiti never wandered more than 60 nm west of our track of two years ago, so I do have a benchmark to compare with.
When we left Hilo, Hawaii, for Nuku Hiva in the Marquesas back in May and June, we encountered an interesting situation. Normally, when moving north or south across the equator, both the temperature and humidity begin increasing about 250 to 300 miles north of the equator, peak near the equator, and then begin lowering as you move farther south, becoming comfortable again about 250 to 300 miles on the other side. This year, about 300 miles north of the equator, everything appeared normal, with the temperature and humidity rising as expected, until about 150 miles north of the line when it began getting chilly. In fact, we had to wear thermal sweatshirts at night while on deck and use blankets to sleep down below.
This cold temperature continued until about 150 miles south of the equator when it suddenly warmed up again and everything continued normally. The currents seemed unaffected, and another boat, Utopia, a few hundred miles ahead of us, reported the same situation. I assumed that the temperature change was caused by an upwelling of cold water, but without a seawater thermometer I had no way of proving my point. Coming north again we had the same situation, with the temperature rising, then cooling off as we neared the equator, and then warming up slightly, but this time not until we got around 480 miles north of the line and about 8° north. The currents were also normal until we got to about 2° south latitude. On November 7 we sailed 101 miles between noon and noon on a generally northerly course. Between 4° south latitude and 2° south, we had a current setting roughly 248° at a 0.79-knot average, or a set of 19 nm for the day.
The next day, November 8, things began changing. Our noon-to-noon run from 3° south latitude to the Equator netted us 109.8 miles, with a current set of 241° for an average of 1.88 knots. A little higher than would be expected, but some of it could have been due to log entry errors. On the 9th, though, the force of the current increased again. Our day's run was 126.8 miles, about normal for our boat Havaiki, but we were set west 50 nm for an average of 2.08 knots at 263°. By this time I was beginning to realize that something was amiss, but the next two days were really exciting, with noon-to-noon runs of 191.7 and 187.1 miles. I couldn't believe it, but, accepted it gladly as we were two days behind our sail plan by that time and could use all the help we could get. By that time, the current was running more northerly and was really giving us a push.
On the 10th, between 2° north and 5° north, the current set us 73 nm at 307°, for an average of 3.04-knots, and the following day, between 5° north and 8° north, we had an even stronger push 76 nm in a direction of 013°, for an average of 3.17 knots. Our best 24-hour run was 207.7 miles between 1600Z on the 10th and 1600Z on the 11th. Having sailed voyaging yachts all my life, it was the first time I've ever had a 200-mile day, and I'll remember it for a long, long time.
Once into the countercurrent we still had stronger currents than normal, about one and a half to two knots, but this time in the proper direction. Since this entire phenomenathe cold weather and the strong currentsoccurred in the Southern Equatorial Current area, it presents a number of questions. Where did the cold water come from? Was it from an upwelling of deeper water, or was it a result of a stronger-than-normal Humbolt Current off South America? If the latter, then why wasn't the westerly flowing current (when it was flowing westerly) much stronger?
My plotting charts show that the northwesterly current covered about 120 miles of latitude, and the northerly current covered some 180 miles, but how wide was this flow? What caused the flow to be northerly over such a large area? How often does this phenomena occur? Is it always there in a year following an El Niño cycle? Or is it always connected with an El Niña cycle?
I only know that I have never run across a discussion of this in any books or magazine articles I have read, nor has it ever come up in any conversation I have had with other voyagers. Perhaps it will help to unlock some of the remaining mysteries of the El Niño/El Niña question.
Things got back to normal, and we found ourselves in the countercurrent fighting a one-knot flow, under overcast skies in the ITZC with rain showers and squalls all around. We were near the northern extremity of the countercurrent and comfortable on deck at midnight wearing shorts and T-shirts again. One thing was for certain, howeverthe rain couldn't dampen the thrill we had a few days before when we reeled off those long days.
I have no idea where that strange current came from, or if I will ever experience it again, but it sure was a blast while it lasted.