Situated between the northeast trades of the northern hemisphere and the southeast trades in the southern hemisphere, the doldrums, also known as the Intertropical Convergence Zone (ITCZ), is an area of low pressure that lies along the equator. In some areas the fickle winds of the doldrums can spread out to span as much as 150 miles and in others this band can be as narrow as 15 miles. So prevalent is this phenomenon that it carries its own weather, which is characteristically hot and muggy, with thunderstorms and squalls that erratically appear with little warning. Thats hardly fitting when you consider that the term doldrum is derived from the Old English for "dull."
Over the years, the doldrums have ingrained themselves in the lore of sailing. French mariners gave this flat, occasionally miserable stretch of the ocean a nickname: Le Pot-au-Noir (the black hole), for its often depressing effects. For sailors bound south from the northern hemisphere, this area is potentially encumbered with problems. Ordinarily, what little wind that exists is punctuated by almost instant squall linesone moment youve got no wind and then in a blink youve got 30 knots pounding away at your sails.
In the doldrums, the humidity and temperatures are usually high and stay uniform throughout the year. Any differences in climate here are linked principally to rainfall patterns. For sailors, the problems in the doldrums can be linked to the equatorial suns relentless and concentrated heat. As the sun heats the air at the oceans surface, that air rises. Naturally sailors prefer the air movement to be horizontal because rising air offers little force for sails, subsequently stopping boats in their tracks. Of course the sun also warms the ocean waters and this adds moisture to the rising air, which ultimately helps produce the frequently violent thunderstorms.
Across the eastern and central Pacific, air currents, moving from the north and south toward the equator, trend westward and form the northeast and southeast trade winds. These winds bring light to moderate rains spotted with brief and sometimes heavy downpours or clear skies. The trade winds combine or give way to the monsoon winds in the far western Pacific, where the alternate cooling and heating of continental Asia produces a seasonal reversal of winds. From about November to March, the northwest monsoon from Asia brings rain to the northerly slopes of New Guinea, and the Solomons. In summer the southeast monsoon reverses the process.
The countercurrents shift south during the northern winter and north during the summer. To either side of the doldrums, the trade winds blow constantly and push great volumes of water westward in the equatorial currents, raising the sea level in the west. Within the doldrums, where strong constant winds are absent, the higher western sea levels flow downward to the east. The Pacific Equatorial Countercurrent is very strong and is definable year-round. The Atlantic Equatorial Countercurrent is strongest off the coast of Ghana (Africa), where it is known as the Guinea Current. The countercurrent of the Indian Ocean flows only during the northern winter and only south of the equator.Nonetheless, despite all of the high-tech weather sensing equipment thats available, along with years of accumulated data and training, the doldrums remain mysterious even for the professionals in the field of meteorology. Recently, in an interview published on www.weatherwise.org, noted weather router Ken Campbell of Commanders Weather said of this phenomenon: "In equatorial regions, I do not know of any way of forecasting cloud development. Basically [when routing sailors], we look for a spot with a narrow or the narrowest band of concentrated clouds and go for it. To a certain extent it is hope and pray, but that is weather forecasting anyway!"
Roger Badham, a well-known New Zealand-based meteorologist and race router concurs: "I use all the high-resolution satellite pictures (infrared, water vapor and visible) for the mean inter-tropical convergence zone position, real time satellite derived winds, and model-predicted winds. We try to skirt all the major cumulonimbus (there are light winds directly underneath these thunderstorms) and use the edges (where downdrafts flow outward), especially at night. Upper-level winds and jet-stream clouds to the north are not used at all."
Where does that leave sailors? Well, Pilot Charts are one source you can check to determine the whereabouts of the doldrums and the narrowest part of the band, but this information tends to be wrong as often as it is right. And getting it wrong can really be costly. No one knows the depressing effects of the doldrums better than French racer Marc Thiercelin. In last years Vendee Globe, Thiercelin was trailing his nearest rival by almost 300 miles as he sailed north approaching the doldrums. With very little to lose (his other nearest opponent was well astern), he effected a brave move that appeared likely to pay off and get him through the band of light winds faster. But the frontal system that he hoped to ride through the doldrums evaporated and left him drifting in zephyrs that swirled around him from almost every direction for the better part of two days.Should you choose to sail through the doldrums any time in the future, go forewarned and go armed with as much information as you can glean. Check out the websites listed below for weather updates, and keep your spirits up and your fingers crossed.
Sailing through a Waterspout by Ralph Doolin
Global Weather Concepts and Fundamentals by Michael Carr
Is the Red Sea Red? by Michael Zezima
Buying Guide: Chartplotters