Big River Running North

Big River Running North: The Gulf Stream

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The Gulf Stream is an impressive natural phenomenon. Its powerful flow is largely unnoticed by many, even those who live close by on the mid-Atlantic and southeastern coast of the U.S., within tens of miles of this dynamic saltwater river. About seventy miles off the coast of North Carolina, the Gulf Stream flows from one to four knots with a volume of seventy million cubic meters per second, 3500 times greater than the Mississippi. In fact, the volume of the Gulf Stream is larger than all the freshwater rivers in the world put together!

The Gulf Stream

The Stream gets its start from the Equatorial Current moving from the African coast, east to west, under the force of the easterly trade winds in the tropical North Atlantic. South America deflects the current northward as it rushes into the Caribbean between islands. A small portion of the current, called the Antilles Current, flows along the northern coasts of Puerto Rico, the Dominican Republic, and Cuba toward Florida. The larger portion of the Equatorial Current circles the Gulf of Mexico, clockwise, exiting through the straits between Cuba and Florida, joining the Antilles Current and officially forming the Gulf Stream.

The Stream then flows in a north and northeasterly direction, eventually turning eastward off the Hatteras coast across the Atlantic where it again divides moving northward, warming the Norwegian coast, and southward along the Iberian Peninsula rejoining the origins of the Equatorial Current. The completed circle, with its clockwise spin, is called the Atlantic Gyre.

To offshore sailors and power cruisers, the bluer and warmer Gulf Stream is very noticeable. An even more noticeable feature is the help or hindrance of the Stream's one to four-knot current. When the flow is opposite to the wind's direction, the Gulf Stream is most obvious due to unusually high and often breaking waves. The crew is generally so seasick that all they can think about is getting out of it alive.

Columbus narrowly missed the Gulf Stream on his homeward passage; Ponce de Leon noticed it in his explorations of Florida; and Benjamin Franklin exploited it for faster passages to Europe. The enormous volume of warm water moved by the Stream toward the colder northeastern portions of the Atlantic, as well as the sinking of this water by the melting freshwater off the polar ice caps, contributes to new theories on global warming trends. In its mysterious ways, the Stream also influences the migration, breeding, and feeding habits of ocean dwellers like juvenile sea turtles, European and American bound eels, magnificent and far ranging blue fin tuna, hundred year old sargassum, armadas of Portuguese man-of-wars and many others.

Today the whereabouts of the Gulf Stream and the eddies it spawns has proven invaluable to commercial shipping, fishing vessels, search and rescue operations, small boat racers and cruisers, and scientists alike.

Satellites and the Stream

The Gulf Stream meanders, snake-like, across the Atlantic much the same way the Mississippi wanders across Middle America. Occasionally, meandering loops pinch off the main Stream forming clockwise circulating warm eddies north of the Gulf Stream and counterclockwise circulating cold eddies south of the Stream. These warm and cold eddies, moving about 2 kilometers per day to the west or southwest, along with the main body of the Stream (moving to the East), are accurately tracked by satellite imagery.

The advent of satellites revolutionized our concept and understanding of the Gulf Stream. The U.S. Department of Commerce National Oceanic and Atmospheric Administration (NOAA) operates a series of satellites managed by the National Environmental Satellite and Information Service (NESDIS). The NOAA Polar Orbiters are spacecraft launched in an 830-870 km, circular, near polar, sun synchronous orbit. The polar operational system consists of two such satellites, one in a morning orbit of 833 km and one in an afternoon orbit at 870 km. Each satellite views the same approximate area twice daily. The Advanced Very High Resolution Radiometer (AVHRR) sensors onboard the satellites detect the (skin) sea surface temperature of the ocean in the infrared channels. NESDIS programmers are continually updating the SST (sea surface temperature) algorithms to reflect reality of the sea surface. SST reports from buoys, ships, and XBT (expendable Bathythermographs) are used as ground truth in the equations. The AVHRR sensors detect ocean surface temperature differences where warm water meets cooler water. Since the Gulf Stream is a very warm current, it is readily detectable in the infrared imagery.

In the 1970’s, a new breed of Oceanographer emerged, the Satellite Oceanographer. In 1973, NOAA began generating an Oceanographic Analysis chart showing the satellite derived location of the Gulf Stream and its associated warm and cold eddies. Jenifer Clark, satellite oceanographer for NOAA, was approached by a sailboat racer in 1976 named Harry Sarazin from Havre de Grace, Maryland. He talked about the possibility of using the Oceanographic Analyses of the Gulf Stream for strategic sailing to take advantage of favorable currents and to avoid unfavorable ones. Little did he know that he initiated the first of a long history of thousands of sailors and boaters using the NOAA Oceanographic Analyses for the same purpose!

Satellite imagery confirmed that the Gulf Stream flows toward the North from Florida to Cape Hatteras, North Carolina. From Cape Hatteras it flows eastward or northeastward across the Atlantic. Warm Sargasso seawater is found south and east of the Stream. Cool Slope Water is normally found north and west of the warm Gulf Stream. Cool Slope Water is found between shore and the Slope Water. Sometimes the SST changes 10 degrees Fahrenheit over a ship's length along the North wall of the Gulf Stream!

Fluid dynamic forces create numerous eddies from Gulf Stream instabilities. When two adjacent Gulf Stream crests come in contact with each other, the result will be the shedding of a cold eddy (CE) circulating counterclockwise, south of the Gulf Stream with cool water on the inside and warm water on the outside of the eddy. Similarly, when two adjacent Gulf Stream troughs come together, the result will be the shedding of a warm eddy (WE) rotating clockwise, north of the Stream, with warm water on the inside and cool water on the outside of it. Warm eddies (WE) are usually found north of the Gulf Stream (GS) and circulate clockwise. SHW is water over the continental shelf and SLW is water over the continental slope.

Once the eddies form in the Gulf Stream, they are very stable instabilities since they are very persistent. Warm eddies have a life cycle of 6-12 months and cold eddies up to 2 years. Although the warm and cold eddies rotate in opposite directions from each other, most eddies translate slowly to the west and southwest. The current speed in the warm eddies varies from 1-2 knots on average. Current speeds associated with cold eddies, counter to text book descriptions and based on actual observations from sailboat racers, is higher than the warm eddy current speeds. These current speeds average 2-3 knots and have been recorded as high as 7 knots (reported by 12 boats in the 1984 Newport to Bermuda Yacht race).

Thousands of users of the NOAA Oceanographic Analyses developed over the years as NOAA worked with the public in meeting user requirements. The National Weather Service routinely used the Oceanographic Analyses to aid in thunderstorm and hurricane prediction and model forecasts. The Coast Guard realized that searching for a ship lost at sea was easier with Gulf Stream flow information. Ship routers used the analyses to take advantage of favorable currents and save fuel. A study was conducted involving a routed ship and an unrouted one. The routed ship took 320 fewer hours to sail from the English Channel to Long Island Sound.

Commercial fishermen have long known the importance of ocean fronts and water temperature in identifying the best area to fish. Fish are known to congregate along temperature fronts that are density barriers separating nutrient rich water from nutrient poor water. In addition, at one time there were around 70 universities using the analyses in graduate studies and in the Oceanography and Meteorology Departments.

The charts generated from analyses of the thermal infrared satellite images were distributed by NOAA in many ways. They were available by subscription fax, radiofax to ships at sea, broadcasts over Coast Guard radio and then free on the Internet. In October 1995, NOAA was subject to budget cuts and downsizing. The entire Ocean Products Center (where the Oceanographic Analysis of the Gulf Stream was produced for many years) was soon eliminated.

Jenifer Clark's Gulfstream

Jenifer Clark decided to retire early but knew she couldn't stop pursuing "her passion". In 1996 she started her own company called Jenifer Clark's Gulfstream. Her charts cover the Gulf of Mexico and the Atlantic to 55W and are updated three times a week. These charts are available to mariners for a nominal fee. Charts are sent via email attachment in color with Satellite SST's or faxed in black and white.

The image below is a sample false color ocean analysis generated by Jenifer Clark's Gulfstream from June 11, 1997. The Continental Shelf (SHW) is false colored in blue and purple where SST’s are in the upper 40's and low 50's. The continental Slope Water (SLW) is false colored in green where the SST's are in the mid to upper 60's. The clockwise circulating warm eddies (WE) are false colored in yellow and light orange. The SST's range from 68-73 degrees Fahrenheit in the WE's. The Gulf Stream (GS) appears in dark orange and brown. SST's are in the upper 70's and low 80's. Counterclockwise circulating Cold Eddies (CE) are found south of the Gulf Stream and are false colored in light orange.

Jenifer Clark's Gulfstream (JCG) specializes in detailed real-time ocean and weather analysis and routing information for marine transit, with core business being bluewater sailboat racing. JCG products and services have been used for several years by world class sailboat racing communities for such events as the: 1997-98 Whitbread Ocean Race, BT Global Challenge, Newport to Bermuda Sailboat Races, Marion to Bermuda Sailboat Races, Annapolis to Bermuda Sailboat Races, Charleston to Bermuda Sailboat Races, Daytona to Bermuda Sailboat Races, Bermuda One-Two Sailboat Races and the Around Alone World Sailboat Race, among others.

Jenifer Clark has over 30 years experience in oceanography and is known in many circles and publications as the "Gulf Stream Lady" because of her lifelong study and expertise involving the Gulf Stream and other world ocean currents. JCG's, Jenifer Clark and her meteorologist husband Dane were exclusively used by the Cruising Club of America to give the weather and ocean briefings at their Captain's meetings prior to the start of Newport to Bermuda Races from 1980 through 1996. Jenifer and Dane have a combined 56 years of service working for the National Atmospheric and Oceanic Administration (NOAA) and are considered experts on Gulf Stream dynamics. In 1998, JCG provided weather and ocean routing information for 84 boats in the Newport to Bermuda Race.

If you will, JCG can be thought of as the "triple A" of the ocean, offering users knowledge of the location and strength of the "rivers" in the ocean; but more specifically, how to take advantage of the favorable "rivers" and avoid the unfavorable ones. Along with weather routing information, JCG can offer a complete environmental package required for strategic route planning, safety considerations and en route tactics. For example, knowledge of locations where surface winds oppose ocean currents is critical because of dangerous high steeply pitched waves that accompany this condition (some call this the "north wall effect"). This condition occurred in the Sidney-Hobart Race in 1998 and caused many of the Whitbread racers during Leg 7 in the Gulf Stream to "surf off the tops of these waves" and drop down in 20+ foot troughs created by this “north wall effect.” Several Whitbread boats had damage and several crewmembers sustained broken limbs and contusions. JCG provided individual routing for 8 of the 9 Whitbread Boats on this Leg from Ft. Lauderdale to Baltimore in 1998. Only one boat chose to steer east avoiding this condition and won the Leg!

For racing or cruising events, JCG offers a complete package service to the Race Committee including: the Captain's Briefing for Weather and Ocean conditions expected during the race, with included handouts and detailed routing information for all participants; or services can be provided to individual boats that want to take advantage of our real-time weather/ocean analysis and forecasts.

Besides sailboat races, JCG routinely supports routing for other vessels including trawlers, tugs and large ocean going vessels for worldwide passage. Recently, a container ship using JCG routing information reported increased speeds across the ground from 17.5 knots (nominal maximum speed) to 22.5 knots over several hundred miles using favorable ocean currents.

JCG has also been the weather/ocean routing choice for several record-breaking ocean passage attempts. These included the 1998 and 1999 solo row attempt by Tori Murden (now the first woman to row across the Atlantic or any ocean), a record swim across the Atlantic by the Frenchman Ben Lecomte, and a record-breaking kayak trip across the Gulf of Mexico.

Navigating the Stream

Getting across the Stream in a small boat can be a challenge. Riding the stream or avoiding it, can mean the difference between winning or losing a sailing race. With accurate information on the position and strength of the stream, any marine vessel can save fuel and/or time by taking advantage of the boost in speed. Fishermen can use the ocean front edges to help them find their catch.

Small boat navigators can successfully cross the stream in a number of ways:

1. Course, set, and drift calculations-The traditional method of navigating an offsetting current is with a vector diagram showing the course, boat speed, set (direction) and drift (speed) of the current. To adjust course to the current, first draw the rhumb line from start to finish. Mark any point A on that line. Then draw a line across point A to represent the set of the current. If the boat speed is 5 knots and the current's speed is 2.5 knots, you'll drift 2.5 miles downstream in one hour. Mark 2.5 miles downstream from A. That's point B. Then, from point B measure your course to your destination. Your actual course may wobble north and south because the speed of the current varies, but you'll reach your destination.

2. GPS waypoint bearings.-With a GPS, the effects of the Gulf Stream current can be easily accounted for. For example, enter the Cat Cay - Gun Cay cut waypoint and head in the direction of the waypoint bearing. Periodically, say every half hour or hour during a ten hour passage, adjust the course based on the automatically updated waypoint bearings. The faster the boat travels, the more frequently this adjustment should be made to account for the offsetting current.

3. GPS autopilot integration-Having an integrated autopilot and GPS offers the simplest method of navigating the Gulf Stream. Simply enter the destination waypoint and let the sophisticated machinery do the work of automatically updating the waypoint bearing and steering the boat.

4. Pre-computed courses-Guidebooks, such as the Southern Waterway Guide, publish lists of popular departure and destination pairs across the Gulf Stream with corresponding magnetic courses to steer. The courses are based on boat speed and the time spent on the Gulf Stream. You should understand the underlying calculation so that you can adjust to the conditions that prevail at the time of your crossing.

Our understanding of the Gulf Stream has grown exponentially since the 70’s. Through the work of Jenifer and Dane Clark, navigating the Gulf Stream can be a safe and comfortable process. Everything from small trawlers to large workboats and container ships can utilize Jenifer Clark's Gulf Stream charts to make routing choices and to use the Stream’s tremendous power to their advantage. The Gulf Stream should never be underestimated. Respect must be given or it will be taken!

If you are interested in finding out more about worldwide JCG services, contact them at 301-952-0930 or e-mail: gulfstrm@erols.com or check out their web site at: http://www.erols.com/gulfstrm or by simply clicking on their advertisement at the top right of the Pilothouse Online home page.

By Dane & Jenifer Clark

Dane is a meteorologist that works closely with Jenifer Clark to provide a professional service for cruisers like you.

Jenifer is a retired satellite oceanographer for NOAA and she is the pioneering force behind Jenifer Clark's Gulf Stream. The knowledge base of Dane and Jenifer on this subject is unparalleled. They are considered experts concerning Gulf Stream and satellite imagery information.