Navigators usually have sufficient accurate data at hand in the form of current tables, pilot charts, coastal pilots, and sailing directions to obtain a reasonably accurate picture of ocean currents involved in reaching their destination. In the Caribbean, however, and particularly in the South Caribbean, these navigational guides are of little definite help. They repeatedly mention the vagaries of the currents, and caution the navigator not to depend too much on the regularity of such currents. For example, “Stress is laid on the fact that even the shipmasters that have had the most experience in approaching Colon from any direction occasionally find themselves far out of their intended position when they had no sights to check their position for a day or less before making land ...” (H.O. Pub. No. 130, 1939).
The number of vessels which have occasion to go to the Panama Canal, and the number of such trips made by each of them, as well as the considerable amount of coastal navigation in this area, would seem to make the subject of Caribbean currents involved in that navigtion an important one.
The total number of trips made by vessels of all classes would seem to make it reasonably possible that accurate and consistent current data would be available. Because of the inconsistency of Caribbean currents, however, little or no reliable data have been formulated. The principal consistency of Caribbean currents is their inconsistency, and the most inconsistent are the countercurrents of the South Caribbean.
This discussion is limited to these countercurrents. Any such specific discussion, however, most conveniently begins with an understanding of the major currents of the Caribbean which are produced by the equatorial currents.
Surface currents result primarily from action of the wind. Surface particles of static water are set into motion by every wind blowing over them; by their friction, these particles transmit their induced motion to the successive strata of water below the surface until a definite current of that body of water is established. The permanence of the set and drift of such a current depends upon the duration, the force, and the direction of the wind.
A secondary cause of currents, particularly of countercurrents, is the difference in density of the water in different regions. These density differences usually are due to differences in temperature, the warmer water being less dense than the colder. In attempting to establish equilibrium of pressure, the water moves from the area of greater temperature to that of lesser, thereby tending to produce a definite current.
The equatorial currents are the product both of wind action and differences in density arising from temperature differences.
The northeast and southeast trade winds over the east Atlantic Ocean form the two major currents known as the north and the south equatorial currents, so designated as to whether they begin in the Northern or Southern Hemisphere. These begin near the west coast of Africa in the vicinity of the equator, and set from east to west toward the Americas with an average drift of about ½ knot. As they approach the Guinea coast, the drift increases to a velocity of from 1½ to as much as 2½ knots, the latter occurring principally during the summer months.
These two equatorial currents merge prior to entering the Gulf of Guiana. This great combined current then flows through the Gulf of Paria and the many passages between the Windward Islands into the Caribbean Sea. At first it maintains its westerly set, then shifts to the northward and westward. As it arrives off the coast of Yucatan, some of the stream passes around Campeche Bank and follows the shore line of the Gulf of Mexico in a clockwise direction. The remainder runs toward Cape San Antonio and the north coast of Cuba. These two components reunite in the Straits of Florida with an easterly set to form that most extraordinary current, the Gulf Stream.
The equatorial current is somewhat affected in its drift by tides. This has been noted particularly in its flow through the Yucatan Passage. Its width also varies, being confined to fairly narrow limits during the winter season, and broadening in the summer months.
Just as in a river, the equatorial current experiences various velocity and directional changes along its course, and has many eddies and countercurrents. Along the Guinea coast and in the Straits of Florida, the set and drift of the main current are fairly well known and reasonably dependable. In its interim passage, however, through the Caribbean and the Gulf of Mexico, it is, to say the least, irregular. It is here that the eddies and counter-currents are most prevalent.
When the southerly part of the equatorial current arrives near the shore of the bight of Costa Rica, the pressure in the bight increases tremendously. Relief is obtained by a portion of the imprisoned water flowing back to the southeastward away from the main current. This is the first of the more important countercurrents of the South Caribbean. It begins near Moin Bay, just northwestward of Port Limon, and extends as far eastward as Gallinas Point, Venezuela, where it dissipates itself back into the major current.
As the greater part of the equatorial current reaches the coast of Yucatan, it strikes against the coast and abruptly changes its set to the northward, with an attendant increase in velocity. Then it passes over Arrowsmith Bank and through the Yucatan Passage at a maximum velocity of 3½ knots. Here the current again divides, one part pouring directly into the Straits of Florida, the other flowing clockwise around the shore line of the Gulf of Mexico.
The higher temperature of the sea in the vicinity of the Straits of Florida, with a proportionately higher pressure, sets up a countercurrent which runs northward along the western side of the Florida peninsula and close ashore to the cooler waters of the northern part of the Gulf; it continues its flow counterclockwise around the shore line of the Gulf of Mexico, inshore of the main stream of the equatorial current. This countercurrent becomes relatively cool and flows back through the Yucatan Passage to the southward under the warmer equatorial stream. From here the submarine current flows along the coasts of the Honduras. As it passes Chinchorro Bank, it flows from under the less dense water of the equatorial current and becomes a surface current. Its velocity is accelerated as it passes into the waters which have been cooled to an even greater extent by the northers.
This countercurrent is fairly dependable in its southerly set in the region of Glover and Lighthouse Reefs and the Turneffe Islands, although its drift is variable. From here its southerly set continues through the inshore passage between Belize and Puerto Barrios, where it turns to the eastward to as far as Patuca Point. At Patuca Point it veers to the southeastward and runs to Cape Gracias a Dios and Punta Gorda, close inshore, with a velocity of about one knot.
As it approaches Bragman’s Bluff, the set is generally south to southwest, with a slightly increased average drift.
On the west side of the Miskito Bank, the current is subject to frequent changes both in set and drift; these changes are quite radical and may occur quite suddenly without apparent cause. In general, however, the current here is southerly in its set.
Among Man of War Cays and Pearl Cays, the current is negligible, except that during the winter months a strong set toward the northeastern shores of these islets is sometimes experienced.
From Bragman’s Bluff inshore to Bluefields, and on to San Juan del Norte, the dominant flow is to the southward. Its drift is greatly influenced by wind and weather. Northers in the winter and heavy rains in the summer usually result in a sudden increase of drift to as much as 3 knots, and in filling the stream with much driftwood. Near Bluefields, the normal current sets south and southeasterly at about 1½ knots. It is worthy of note that on occasion and for no apparent reason, this current will here reverse itself and run to the northward for several hours at a velocity of about ½ knot, then will shift back to its normal set.
As the current passes San Juan del Norte, it sweeps southeastward along the coast to Moin Bay where it joins with the previously mentioned countercurrent which has its beginning in that region. Here the countercurrent runs toward the coast with a drift of from 2 to 3 knots, causing a heavy ground swell along the whole shore.
From Moin Bay and Port Limon, the set is more southeasterly. It runs close inshore and accelerates somewhat. Upon reaching Almirante Bay, a portion of the current enters Boca del Drago and emerges at Boca del Toro, running along the southerly shore of Isla de Colon. This portion of the countercurrent is affected by the tides, thereby resulting in some varying effect upon the greater part of the current when the two rejoin outside Boca del Toro.
The current continues its southeasterly flow from Almirante Bay to Cape Valiente. At the latter point, the projecting cays and the currents out of Chiriqui Lagoon divert the main countercurrent to a more easterly direction across the mouth of the Golfo de los Mosquitos, and reduce its velocity to about one knot.
From Cape Valiente to as far eastward as Gallinas Point, the main countercurrent is about 30 miles in width.
The fairly abrupt change in the set of the current off Cape Valiente causes a slight westerly eddy to run inshore between Brujas Point, near Colon, eastward to Pena Valiente. It is quite narrow but is readily apparent when any driftwood is present. This eddy has often been used by the writer to advantage in proceeding southwestward from Colon.
The easterly set of the main countercurrent continues from Chiriqui Lagoon offshore of a fairly regular coastline with a velocity of about one knot. At Brujas Point it is deflected more to the north of east until it passes Colon, running fairly parallel to the shore.
About 6 miles northeast of the breakwater at Colon the bottom contour abruptly deflects the current to the northeast. This change is quite radical and creates a readily apparent “wall” of water.
From this point the current maintains its northeasterly course past Porto Bello and over Salmedina Reef. Here it veers to the eastward to Los Farralones where it has a normal drift of one knot but sometimes attains a drift of as much as 3 knots, and sometimes disappears or even reverses itself. The latter occurs particularly after extended easterly winds.
In this particular area, which is the usual landfall in approaching the Panama Canal from the northward and eastward, the currents are quite variable, especially during the summer months. When it has been impossible to get a late fix by observation, the navigator may well expect to find his ship several miles either to the east or west of his dead-reckoning position.
During the late dry season and the rainy season of 1942, this writer has made the run between Los Farralones and the entrance to Colon over a hundred times in each direction. These runs were made under various conditions of wind and weather, but all at an engine speed which would give 8 knots in still water. The ship in which the runs were made is of fairly shallow draft, and has considerable windage forward. It was found that the courses made good on the southwesterly runs varied over an arc of some 20 degrees. On some of these runs it was not possible to hold the compass course and reach the breakwater because the ship had been set too far inshore. On the northeasterly runs, the courses made good varied no more than 18 degrees.
Onshore winds usually maintain the normal set of the current in this area. Fresh westerly winds will increase the drift. Prolonged easterly winds, however, will decrease the drift and sometimes even cause the current to reverse itself.
On one occasion, in the height of the rainy season, while anchored about 2 miles off Colon breakwater, a current of 3 knots setting to the eastward was noted by this same ship. Fresh winds from the southeast over a period of less than 48 hours caused a reversal of the current to the westward with a velocity of ¾ knot.
Considerable time spent at anchor in this area has given the writer adequate opportunity to study the currents in that vicinity. It has been noted that, particularly during the rainy season, exceptionally calm seas usually are accompanied by a decrease in the drift, and often by a reversal of the normal current. This reversed current, however, existed only in the upper strata of water; at depths of as little as 12 feet, the normal easterly set was encountered.
The tidal currents off Colon are negligible. The mean rise and fall is about one foot, and never varies over 2 feet. Its height is affected more by wind direction than by any other factor.
In the area of about 40 miles radius from Colon, westerly winds usually bring rain and flooded rivers, resulting in much driftwood being poured into the sea. This driftwood often is found as far as 30 miles offshore; when encountered, the navigator may reasonably assume that westerly winds have prevailed and the easterly set is stronger than usual, and should make allowance for this current.
Between Los Farralones and Manzanillo Point, the countercurrent has its greatest normal velocity. It generally sets to the northeast with a not unusual drift of 3½ knots. After passing Manzanillo Point, it lets to the eastward and southeastward, following the shore line to Puerto Carreto where the discharge of Rio Atrato through the Golfo de Darien deflects it to the eastward and northeastward on which course it continues as far as Isla Fuerte and Isletas de San Bernardo. Its velocity is reduced to no more than 2 knots, and is fairly susceptible to influence of the wind. On one occasion, a number of years ago, the current in this region reversed itself when a hurricane was in progress over Yucatan Passage, some 800 miles distant.
An eddy between Punta de la Revesa and Punta Cayman in the Darien Gulf has a set to the northwest with a drift of about 2 knots.
Across the mouth of Golfo de Morrosquillo, the countercurrent usually does not produce an eddy, but does induce a minor current within the gulf itself, which must be taken into consideration when navigating therein.
From the Isletas de San Bernardo to the Isletas de Rosario, the countercurrent sets north-northeast with an average drift of 1½ knots. In the more confined waters among these small islands, drifts of as high as 3 knots have been observed. The currents here, however, are so subject to effect of wind and other factors that they are thoroughly inconsistent.
The great river, Rio Magdalena, emptying into the sea in the vicinity of Cartagena, tends to reduce the velocity of the countercurrent and deflect it more to the northward. The current continues to flow along the coast line until it reaches Gallinas Point where it is deflected into and joins again with the equatorial current.
From the foregoing it is obvious that although the general movement of the countercurrent is continued from the westward to the eastward along the southern coast of the Caribbean, it is quite impracticable to set forth positive sailing directions which would be accurate and dependable. There are some few suggestions, however, which might be of aid to the navigator in plotting his courses in these waters:
- Caribbean currents generally are strongest in the rainy season.
- Caribbean currents are most erratic during the rainy season.
- The main currents, far offshore, usually set from east to west.
- The countercurrents, closer inshore, usually set from west to east.
- A glassy sea usually indicates a slackening or even a reversal of the countercurrents.
- Large quantities of driftwood sighted at sea usually indicate recent westerly winds with a resultant stronger eastward countercurrent.
- Caribbean currents are consistent only in their inconsistency.