The NWS has long had an extensive network of surface weather observing stations located all over the country, routinely reporting such data as atmospheric pressure, humidity, temperature, visibility, wind direction and velocity, the type and percentage of cloud cover, and the type and quantity of precipitation. Consequently, through this network, the NWS knows both what is going on now in the atmosphere at many points scattered across the country, and what has happened at these locations in the recent past. With this knowledge, they can predict with great accuracy what the atmosphere will do in the near future. The advent of satellite observations has vastly extended and improved the fund of atmospheric information available to the NWS by providing real-time views of major weather systems worldwide. Using satellite observations, it has become routine procedure to track large-scale atmospheric phenomena, such as air-mass formation and movement, weather fronts, and tropical and extratropical cyclonic systems. Major weather systems can now be tracked by satellite from their inception, through their development, all the way to their final dissolution. Coupled with surface observations, this allows analysts to see — generally days ahead of time — what conditions are likely to develop on the U.S. East Coast, the West Coast, across the country and over portions of the oceans. Appropriate warnings can also be issued of severe weather disturbances that may cause inconvenience, injuries or property damage. Although there are many automated, land-based stations collecting and transmitting surface weather observations to the NWS, about two-thirds of the earth’s surface is water. Over vast ocean areas, major weather systems constantly develop, change, move and dissipate far beyond the range of any land-based observation networks. Satellite observation of the oceans reveals a great deal about large-scale weather systems passing over the oceans, but the type of detailed information on surface conditions over the oceans — such as air temperature, atmospheric pressure, humidity, cloud cover, visibility and winds — surface data of the type supplied by land-based observing stations, has been missing. Here the NDBC enters the picture. It performs four major tasks that provide a vast amount of the needed information. First, it maintains a network of floating buoys that are moored at sea and are equipped with automated weather-observing instruments whose readings are transmitted hourly by satellite to NWS headquarters. These reports consist of the same type of information already being generated by the land-based surface stations: surface temperature, pressure, humidity, cloud cover, precipitation, winds and visibility. In addition, they include information on sea conditions, such as sea temperature, wave height and swell direction. Second, the NDBC maintains a Coastal-Marine Automated Network (C-MAN) of surface observing stations. Some are located in now-automated lighthouses that were manned by U.S. Coast Guard personnel who reported local surface weather observations. Others are strategically located on capes, beaches, near-shore islands or offshore platforms. These stations also transmit the same type of observations as the other surface stations. Third, it coordinates the Volunteer Observing Ship program supplying the NWS with regular surface reports from a vast number of civilian merchant ships plying the oceans worldwide. Fourth, it operates the Deep-ocean Assessment and Reporting of Tsunamis (DART) network. This network alerts a group of Tsunami Warning Centers when a tsunami has started, where it is and where it is headed. The moored-buoy network Moored buoys are placed in various areas of the coastal and offshore waters of the western North Atlantic along the U.S. East Coast. Also around eastern European waters from southern Norway to west of the British Isles, then continuing on southward as far as northern Portugal. Buoys are also moored in large areas of the western Pacific Ocean from the Bering Sea, south to around Hawaii, and along the west coasts of Alaska, Canada and the United States. They are also located down a strip of the central tropical Pacific Ocean. Moored buoys are of several different types. The one chosen for a particular place depends on the conditions it will face. Most of them are round discus buoys of various sizes, the largest being the 12-meter (40-foot) model. Other sizes of this buoy type are the 10-meter (33-foot) and 3-meter (10-foot), plus two types of 2.4-meter (8-foot) coastal, and the 1.5-meter (5-foot) Coastal Oceanographic Line-of-Sight (COLOS) buoys. Since the COLOS series was part of a project that is now completed, these buoys have been deactivated. Most of the 12-meter steel-hulled, discus-type buoys were discontinued because the anticorrosion maintenance became too expensive, particularly as compared with the 3-meter discus units, which, having an aluminum hull, are protected from corrosion. One additional type of buoy is also in use. This one is designated as the Nomad. It is 6 meters (20 feet) long and boat-shaped. It also has an aluminum hull, reducing its susceptibility to corrosion, and the magnetic effects of the hull on its compass are minimal. Its hull shape makes it highly directional and thus quick to respond to directional wind and sea changes. There have been no known capsizings of the 6-meter Nomads. The choice of buoy hull type depends on the intended location and the wind and sea conditions to which the buoy will be exposed. The steel hulls of the 12-meter discus buoys make them very sturdy and capable of withstanding the extremely severe weather of the Bering Sea where the last two are deployed. The 10-meter steel-hulled discus is less expensive to maintain, but they have been known to capsize on occasion in severe wind and sea conditions. Both of these larger buoy types must be towed by the Coast Guard to their assigned locations, as they are too large to be carried aboard the Coast Guard ships that place them on station. The 3-meter discus and the 6-meter Nomad are aluminum hulled, considerably less expensive to build and maintain than the larger types, but not nearly as rugged under severe conditions. They have the great advantages of being much easier to handle and move about than larger buoys, and, being aluminum hulled, are easier to maintain. The mooring systems are based on the buoy hull type, severity of wind and sea conditions expected, and water depth. A small buoy in shallow coastal waters will hold satisfactorily on an all-chain rode. As the buoy becomes larger and the water deeper, the mooring line is changed to combinations of chain, nylon and buoyant polypropylene. Mooring systems are designed for a two-year service life; however, some of the deep combination moorings have held up in service for as long as 10 years. Both the sensing and radio transmission systems on all buoys are powered by batteries that are charged by solar cells. The offshore servicing of the moored buoys is handled by the Coast Guard, and all buoys are serviced as required to repair damaged or degraded equipment. In addition, they are serviced every two years for routine maintenance and installation of newly calibrated sensors. Coastal-Marine Automated Network C-MAN was set up for the NWS during the early 1980s. When the Coast Guard proceeded with its Lighthouse Automation and Modernization Program, the NWS still needed many of the meteorological observations that had been made by Coast Guard personnel at the automated lighthouses. These were replaced by automated C-MAN weather observing stations. There now are 60 C-MAN stations, some in automated lighthouses and others in specially built structures on capes, beaches, near-shore islands or offshore islands. Fourteen of these stations are also located on the Marshall and Caroline Islands in the western Pacific. Like the automated buoys, these stations transmit hourly barometric pressure, air temperature, wind speed and direction, gust velocity, relative humidity, precipitation and visibility. The structures of these stations vary with their locations and the conditions under which they are expected to operate. Cape Arago, Ore., is an example of a C-MAN station located in an existing lighthouse that has been automated. Some others are located in existing lights that have long been automated, such as Fowey Rocks, Fla. In a many cases, additional C-MAN stations have been placed at points chosen by the NWS where no aid to navigation existed. While some C-MAN stations are conveniently located to use AC power, others, like the moored buoys, rely on batteries charged by solar cells. Like the buoys, these stations are serviced as needed to repair damaged equipment; otherwise, they too are routinely serviced on a two-year schedule. Volunteer Observing Ship program The moored-buoy and C-MAN programs give the NWS regular surface condition reports covering many offshore and inshore ocean locations. However, vast areas of open ocean still remain far beyond the range of the existing buoy and C-MAN network. This is where the VOS program provides vital information. These volunteering ships are a wide variety of ordinary merchant ships going about their normal business of picking up and delivering cargo between seaports worldwide. This is an international program operating under the auspices of the World Meteorological Organization. Participating ships are from 49 countries, and the information they supply is shared by all the countries involved. The United States has 950 participating ships. On every ship, at all times while underway, a watch officer on the bridge is in charge of the operation of the ship. One of the officer’s duties is to note the weather conditions during the watch for entry in the ship’s log. This includes barometer reading, air temperature, humidity, wind speed and direction, visibility, cloud cover, sea state (wave height and direction), and precipitation, if any. The ships transmit this information that they are also routinely noting in the ship’s log to the NWS via Inmarsat. The NWS asks them to report their observations every six hours when in open ocean more than 200 nm from land (0000Z, 0600Z, 1200Z, etc). When within 200 nm of the U.S. coast, they are asked to report every three hours (0000Z, 0300Z, 0600Z, 0900Z, etc). In ocean areas where data is sparse, or if they happen to be in an area of significant weather disturbance, such as a tropical storm or hurricane, they are asked to report hourly. Since they are constantly in transit, these ships include their geographic location along with each weather report. Location is unnecessary in the reports from moored buoys and C-MAN stations, as each of their fixed locations is known. The ship’s position information is a vital part of VOS reports, so the NWS can fit them into the overall picture of developing and changing atmospheric conditions. QuikScat One of the advances in satellite technology and instrumentation of special concern to marine interests is the ability to detect surface wind speed and direction over the oceans. This is accomplished by Seawinds-QuikScat, a polar-orbiting, sun-synchronous satellite equipped with a sensing instrument that estimates surface wind speed and direction by measuring reflection/scattering off ocean surface waves. The potential of this technology is immense, since it provides important surface data concerning conditions on open water in areas not available in any other way. Unfortunately, there are limitations to this new technology. Since the satellite producing it is polar-orbiting rather than geostationary, the data concerning any particular area is only available twice daily. In addition, heavy rain can make it difficult to know whether surface wind estimates are accurate. Satellite data of this kind becomes far more useful when used in conjunction with ship-based observations. Take the example of a storm over the Bering Sea on Dec. 27, 2002. A QuikScat image of the northern part of the storm showed many wind barbs close to the center of the storm, indicating winds in the 60- to 70-knot range. A VOS located at a point somewhat to the west of the maximum winds shown on the QuikScat image reported winds of 50 knots. On the QuikScat image at the reporting point, the winds showed as 40 to 45, indicating that the satellite image was probably quite close to the truth. In other cases, VOS reports showed QuikScat estimates to be seriously in error. Deep-ocean Assessment and Reporting of Tsunamis In addition to the floating buoy network reporting surface observations, as of 2003, the NDBC took over operation of the DART system. The main purpose of this program is to reduce the loss of life and property resulting from tsunami impacts on coastal communities by means of timely warnings. The secondary purpose is to eliminate false alarms and the attendant expense and confusion of unnecessary evacuations. The DART network consists of an array of deep-ocean detection stations that provide real-time tsunami warnings to the NWS. From the propagation characteristics of the wave, the NWS can determine which coastal areas should be warned and which will be unaffected. Each DART station has two major parts: an ocean Bottom Pressure Recorder and a surface buoy. The BPR measures the ocean depth and transmits its measurement to the buoy attached above it. The buoy then transmits this information via satellite to the NWS. The BPR is moored at depths ranging from 10,000 to about 16,000 feet and contains an electronic pack and batteries adequate to supply power for two years. The surface buoy contains the transmitter that communicates with the Geostationary Operational Environmental Satellite (GOES) and a battery pack adequate to power it for one year. Mean water-level changes of more than 3 centimeters (1 inch) indicate the presence of a tsunami. At that point, the device goes into tsunami mode, causing the BPR to update its surface buoy continuously with water-level averages that are transmitted to the Tsunami Warning Centers, which can then determine if warnings should be issued and to which coastal areas. The information regarding weather conditions, particularly at surface level, over the huge areas of our planet’s oceans has always been a problem at the NWS. Modern technology as utilized by the NDBC has quietly made vast improvements in both the quantity and quality of the data now available. The ever-improving fund of real-time satellite data can now be cross-checked and corrected as necessary by the combination of instrumented moored buoys, C-MAN stations and ship-based observations. As the fleet of VOS expands, the importance of their contribution will increase. In addition, the DART system provides the NDBC with a new powerful tool in its mission of reporting dangerous conditions over the world’s seas. Jeff Markell is a freelance writer and the author of Sailor’s Weather Guide, Second Edition, published by Sheridan House Publishers.
Second,
the
NDBC
maintains
a
Coastal-Marine
Automated
Network
(C-MAN)
of
surface
observing
stations.
Some
are
located
in
now-automated
lighthouses
that
were
manned
by
U.S.
Coast
Guard
personnel
who
reported
local
surface
weather
observations.
Others
are
strategically
located
on
capes,
beaches,
near-shore
islands
or
offshore
platforms.
These
stations
also
transmit
the
same
type
of
observations
as
the
other
surface
stations.
Third,
it
coordinates
the
Volunteer
Observing
Ship
program
supplying
the
NWS
with
regular
surface
reports
from
a
vast
number
of
civilian
merchant
ships
plying
the
oceans
worldwide.
Fourth, it operates the Deep-ocean Assessment and Reporting of Tsunamis (DART) network. This network alerts a group of Tsunami Warning Centers when a tsunami has started, where it is and where it is headed.
The moored-buoy network
Moored buoys are placed in various areas of the coastal and offshore waters of the western North Atlantic along the U.S. East Coast. Also around eastern European waters from southern Norway to west of the British Isles, then continuing on southward as far as northern Portugal. Buoys are also moored in large areas of the western Pacific Ocean from the Bering Sea, south to around Hawaii, and along the west coasts of Alaska, Canada and the United States. They are also located down a strip of the central tropical Pacific Ocean.
The moored buoys measure and transmit hourly via satellite the barometric pressure, wind direction and average velocity, as well as maximum wind-gust velocity, and air and sea temperatures. In addition, they give wave information such as height, period and, in many cases, swell direction.
Moored buoys are of several different types. The one chosen for a particular place depends on the conditions it will face. Most of them are round discus buoys of various sizes, the largest being the 12-meter (40-foot) model. Other sizes of this buoy type are the 10-meter (33-foot) and 3-meter (10-foot), plus two types of 2.4-meter (8-foot) coastal, and the 1.5-meter (5-foot) Coastal Oceanographic Line-of-Sight (COLOS) buoys.
Since the COLOS series was part of a project that is now completed, these buoys have been deactivated. Most of the 12-meter steel-hulled, discus-type buoys were discontinued because the anticorrosion maintenance became too expensive, particularly as compared with the 3-meter discus units, which, having an aluminum hull, are protected from corrosion.
One additional type of buoy is also in use. This one is designated as the Nomad. It is 6 meters (20 feet) long and boat-shaped. It also has an aluminum hull, reducing its susceptibility to corrosion, and the magnetic effects of the hull on its compass are minimal. Its hull shape makes it highly directional and thus quick to respond to directional wind and sea changes. There have been no known capsizings of the 6-meter Nomads.
The choice of buoy hull type depends on the intended location and the wind and sea conditions to which the buoy will be exposed. The steel hulls of the 12-meter discus buoys make them very sturdy and capable of withstanding the extremely severe weather of the Bering Sea where the last two are deployed. The 10-meter steel-hulled discus is less expensive to maintain, but they have been known to capsize on occasion in severe wind and sea conditions. Both of these larger buoy types must be towed by the Coast Guard to their assigned locations, as they are too large to be carried aboard the Coast Guard ships that
place them on station.
The 3-meter discus and the 6-meter Nomad are aluminum hulled, considerably less expensive to build and maintain than the larger types, but not nearly as rugged under severe conditions. They have the great advantages of being much easier to handle and move about than larger buoys, and, being aluminum hulled, are easier to maintain.
The mooring systems are based on the buoy hull type, severity of wind and sea conditions expected, and water depth. A small buoy in shallow coastal waters will hold satisfactorily on an all-chain rode. As the buoy becomes larger and the water deeper, the mooring line is changed to combinations of chain, nylon and buoyant polypropylene. Mooring systems are designed for a two-year service life; however, some of the deep combination moorings have held up in service for as long as 10 years.
Both the sensing and radio transmission systems on all buoys are powered by batteries that are charged by solar cells. The offshore servicing of the moored buoys is handled by the Coast Guard, and all buoys are serviced as required to repair damaged or degraded equipment. In addition, they are serviced every two years for routine maintenance and installation of newly calibrated sensors.
Coastal-Marine Automated Network
C-MAN was set up for the NWS during the early 1980s. When the Coast Guard proceeded with its Lighthouse Automation and Modernization Program, the NWS still needed many of the meteorological observations that had been made by Coast Guard personnel at the automated lighthouses. These were replaced by automated C-MAN weather observing stations. There now are 60 C-MAN stations, some in automated lighthouses and others in specially built structures on capes, beaches, near-shore islands or offshore islands. Fourteen of these stations are also located on the Marshall and Caroline Islands in the western Pacific.
Like the automated buoys, these stations transmit hourly barometric pressure, air temperature, wind speed and direction, gust velocity, relative humidity, precipitation and visibility. The structures of these stations vary with their locations and the conditions under which they are expected to operate.
Cape Arago, Ore., is an example of a C-MAN station located in an existing lighthouse that has been automated. Some others are located in existing lights that have long been automated, such as Fowey Rocks, Fla. In a many cases, additional C-MAN stations have been placed at points chosen by the NWS where no aid to navigation existed.
While some C-MAN stations are conveniently located to use AC power, others, like the moored buoys, rely on batteries charged by solar cells. Like the buoys, these stations are serviced as needed to repair damaged equipment; otherwise, they too are routinely serviced on a two-year schedule.
Volunteer Observing Ship program
The moored-buoy and C-MAN programs give the NWS regular surface condition reports covering many offshore and inshore ocean locations. However, vast areas of open ocean still remain far beyond the range of the existing buoy and C-MAN network. This is where the VOS program provides vital information.
These volunteering ships are a wide variety of ordinary merchant ships going about their normal business of picking up and delivering cargo between seaports worldwide. This is an international program operating under the auspices of the World Meteorological Organization. Participating ships are from 49 countries, and the information they supply is shared by all the countries involved. The United States has 950 participating ships.
On every ship, at all times while underway, a watch officer on the bridge is in charge of the operation of the ship. One of the officer's duties is to note the weather conditions during the watch for entry in the ship's log. This includes barometer reading, air temperature, humidity, wind speed and direction, visibility, cloud cover, sea state (wave height and direction), and precipitation, if any.
The ships transmit this information that they are also routinely noting in the ship's log to the NWS via Inmarsat. The NWS asks them to report their observations every six hours when in open ocean more than 200 nm from land (0000Z, 0600Z, 1200Z, etc). When within 200 nm of the U.S. coast, they are asked to report every three hours (0000Z, 0300Z, 0600Z, 0900Z, etc). In ocean areas where data is sparse, or if they happen to be in an area of significant weather disturbance, such as a tropical storm or hurricane, they are asked to report hourly.
Since they are constantly in transit, these ships include their geographic location along with each weather report. Location is unnecessary in the reports from moored buoys and C-MAN stations, as each of their fixed locations is known. The ship's position information is a vital part of VOS reports, so the NWS can fit them into the overall picture of developing and changing atmospheric conditions.
QuikScat
One of the advances in satellite technology and instrumentation of special concern to marine interests is the ability to detect surface wind speed and direction over the oceans. This is accomplished by Seawinds-QuikScat, a polar-orbiting, sun-synchronous satellite equipped with a sensing instrument that estimates surface wind speed and direction by measuring reflection/scattering off ocean surface waves. The potential of this technology is immense, since it provides important surface data concerning conditions on open water in areas not available in any other way. Unfortunately, there are limitations to this new technology. Since the satellite producing it is polar-orbiting rather than geostationary, the data concerning any particular area is only available twice daily. In addition, heavy rain can make it difficult to know whether surface wind estimates are accurate. Satellite data of this kind becomes far more useful when used in conjunction with ship-based observations.
Take the example of a storm over the Bering Sea on Dec. 27, 2002. A QuikScat image of the northern part of the storm showed many wind barbs close to the center of the storm, indicating winds in the 60- to 70-knot range. A VOS located at a point somewhat to the west of the maximum winds shown on the QuikScat image reported winds of 50 knots. On the QuikScat image at the reporting point, the winds showed as 40 to 45, indicating that the satellite image was probably quite close to the truth. In other cases, VOS reports showed QuikScat estimates to be seriously in error.
In many cases, VOS reports in conjunction with QuikScat images have helped forecasters determine when, where and whether to issue gale or storm warnings. QuikScat shows what an advanced observing device can deduce from miles out in space. The VOS report shows what is actually happening on surface level at a specific point within the larger area covered by the satellite image and thus helps either to prove or disprove the accuracy of that image. As experience with this technology grows, so will the ability of observers to detect and correct errors.
Deep-ocean Assessment and Reporting of Tsunamis
In addition to the floating buoy network reporting surface observations, as of 2003, the NDBC took over operation of the DART system. The main purpose of this program is to reduce the loss of life and property resulting from tsunami impacts on coastal communities by means of timely warnings. The secondary purpose is to eliminate false alarms and the attendant expense and confusion of unnecessary evacuations.
The DART network consists of an array of deep-ocean detection stations that provide real-time tsunami warnings to the NWS. From the propagation characteristics of the wave, the NWS can determine which coastal areas should be warned and which will be unaffected.
Each DART station has two major parts: an ocean Bottom Pressure Recorder and a surface buoy. The BPR measures the ocean depth and transmits its measurement to the buoy attached above it. The buoy then transmits this information via satellite to the NWS. The BPR is moored at depths ranging from 10,000 to about 16,000 feet and contains an electronic pack and batteries adequate to supply power for two years. The surface buoy contains the transmitter that communicates with the Geostationary Operational Environmental Satellite (GOES) and a battery pack adequate to power it for one year.
Mean water-level changes of more than 3 centimeters (1 inch) indicate the presence of a tsunami. At that point, the device goes into tsunami mode, causing the BPR to update its surface buoy continuously with water-level averages that are transmitted to the Tsunami Warning Centers, which can then determine if warnings should be issued and to which coastal areas.
The information regarding weather conditions, particularly at surface level, over the huge areas of our planet's oceans has always been a problem at the NWS. Modern technology as utilized by the NDBC has quietly made vast improvements in both the quantity and quality of the data now available. The ever-improving fund of real-time satellite data can now be cross-checked and corrected as necessary by the combination of instrumented moored buoys, C-MAN stations and ship-based observations. As the fleet of VOS expands, the importance of their contribution will increase. In addition, the DART system provides the NDBC with a new powerful tool in its mission of reporting dangerous conditions over the world's seas.
Jeff Markell is a freelance writer and the author of Sailor's Weather Guide, Second Edition, published by Sheridan House Publishers.
