The coastal weather station

NDBC built the Coastal-Marine Automated Network for the National Weather Service in the early 1980s. Coast Guard crews at light stations had long made weather observations. As the Coast Guard automated its lights, those observations would have ended, and automatic stations took their place. NDBC dates the network to 1981, with its core complete by 1985. It grew to about 60 stations on lighthouses, capes and beaches, islands near shore and offshore platforms; NDBC's 2023 handbook counts 40.

A C-MAN station measures what a buoy's weather sensors measure, and its data are processed and sent to shore in almost the same way. But it stands still: it needs no compass, its sensors can be mounted high above the water, and it doesn't measure waves from its own motion.

Bluegraph lists 172 coastal stations, and NDBC carries all their reports. NDBC operates 33, all C-MAN stations. The Marine Exchange of Alaska operates 67 around Alaska's coast. National Weather Service forecast offices operate 35: 33 around the Great Lakes, from Duluth to Buffalo, and two on lakes in South Carolina. The Texas Coastal Ocean Observing Network operates 18 at its water-level stations, which is why their names begin with a 7-digit water-level station number. The Federal Aviation Administration operates 9, on oil and gas platforms in the Gulf; NOAA's National Ocean Service 3, two of them in its PORTS harbor systems; and universities and laboratories 7: Scripps at La Jolla, Moss Landing Marine Laboratories, Dauphin Island Sea Lab, CORMP and Florida Tech.

The count uses the owner named in NDBC's station table (read October 27, 2026). It agrees with the owners Bluegraph recorded when it added the stations, and with the station pages we sampled. NDBC classifies 42 of the 172 as C-MAN stations: its own 33, and 9 operated by others.

The figure shows NDBC's station TPLM2 on Thomas Point Shoal Light, in Chesapeake Bay near Annapolis, Maryland. Built in 1875, the light is a hexagonal cottage 35 feet (10.7 m) across on seven iron screwpiles 10 inches (25 cm) across, one in the middle and six around it, with tons of riprap (loose stone) placed around them over the years. Its lantern is 43 feet (13.1 m) above mean high tide; it was automated in 1986. NDBC's mast stands beside the lantern. According to the station page, the anemometers are 18 m above the water, the air-temperature sensor 17.4 m and the barometer 12.2 m above mean sea level, on a MARS payload.

Coastal stations vary far more than buoys do. They stand on lighthouses, piers, platforms, towers and docks, and their sensors are mounted at whatever height the structure allows: the anemometer is 18 m above the water at Thomas Point, 20.2 m on the pier at La Jolla, and 3.2 m above a site 4.3 m above mean sea level at Morgans Point, Texas. Payloads differ too: of NDBC's 33, 20 carry the older SM+ payload, 7 carry MARS like Thomas Point, 2 ARES, 2 SCOOP and 2 a Sutron XPERT. The figure shows one station, not a type.

C-MAN stations carry two propeller-vane anemometers on a crossarm, a primary and a backup. Each is a propeller kept facing into the wind by a tail, like R.M. Young's Wind Monitor: an 18 cm four-bladed propeller on a body 55 cm long, which starts to turn at about 1 m/s. The propeller's speed gives the wind speed, and the tail's direction gives the wind direction. On a fixed station, the sensors are aligned with true north when they are mounted; a buoy needs a compass instead.

Thomas Point's payload samples the wind once a second for 2 minutes, once an hour. The reported speed is the mean of those samples; the gust is the highest 5-second running mean among them. Stations with the newer SCOOP payload average over 10 minutes, six times an hour. NDBC states its winds as accurate to 1 m/s or 10% in speed, and 10° in direction.

The water drags on the air above it, so wind slows toward the surface, most sharply close to it. Over the sea, in air about as warm as the water, the speed increases roughly as height to the power 0.11, a rule Hsu, Meindl and Gilhousen derived from measurements in the Gulf of Mexico and off Chesapeake Bay. By that rule, the wind at the standard height of 10 m is about 6% less than at Thomas Point's 18 m, and the wind at a discus buoy's 3.8 m is about 16% less. The arrows in the figure follow this rule, and a vertical line of marked air, released where the arrows start, bends into the same shape as it blows downwind. In warmer or cooler air, the profile changes.

So a wind reading means little without its height, and the winds at two stations can be compared only with their heights in mind. NDBC also estimates each station's wind at 10 m and 20 m from the measured speed, the anemometer's height, and the air and sea temperatures, using the method of Liu, Katsaros and Businger. It assumes 85% humidity and standard pressure, and neutral air when a temperature is missing. Bluegraph shows the wind as measured, at the station's own height. The discus buoy measures it 3.8 m up.

Air temperature is measured inside a radiation shield: a stack of white plates, about 12 cm across, that shades the sensor from the sun and lets the wind blow through between them. Many C-MAN stations rely on these naturally ventilated shields, because a fan to draw air through takes more power than a station can spare. In strong sun and light wind, the air inside warms and the reading runs high. On moored buoys, which carry the same kind of shield, Anderson and Baumgartner measured a mean daytime error of 0.27 °C and a maximum of 3.4 °C, increasing with sunshine and decreasing with wind.

The sensors are thermistors. The MARS payload carries a separate dew-point sensor; relative humidity is calculated from the two on shore. NDBC states air temperature and dew point as accurate to 1 °C.

An aneroid barometer measures pressure, 12.2 m above mean sea level at Thomas Point, as a 2-minute mean once an hour. On shore, NDBC reduces it to sea level using the Weather Service's method, so that stations at different heights can be compared, and reports the change over 3 hours. It states pressure as accurate to 1 hPa. The figure puts the barometer in the payload's box, at its published height; its exact position is not published.

Where a C-MAN station measures sea temperature, a thermistor is fixed at a set distance above the bottom, so its depth below the surface changes with the tide. Thomas Point's page lists one 1 m below mean lower low water, but the station reported no sea temperature in the six weeks to late October 2026, and it doesn't measure waves.

Each hour the payload sends its report to a GOES weather satellite, which relays it to NOAA's ground station at Wallops Island, Virginia; NDBC usually publishes it within half an hour. From Thomas Point, GOES East is over the equator at 75.2° W, almost due south and about 45° above the horizon. The two SCOOP stations, Long Key and Sand Key in Florida, instead report every 10 minutes by Iridium satellite.

NOAA's National Ocean Service operates weather sensors at many of its water-level stations, beside the tide gauge, and in its PORTS systems in busy harbors. They follow its own rules: every sensor reports every 6 minutes. The wind is a 2-minute mean of 1-second samples before each tenth of an hour, its direction a mean of unit vectors, and the gust the highest 5-second mean in the 6 minutes. The anemometer, an R.M. Young like NDBC's or a sonic sensor with no moving parts, should be at least 10 m above the water and 10 m clear of obstacles where the site allows. Air temperature is 20 samples over 2 minutes, accurate to 0.2 °C; pressure is accurate to 0.5 hPa.

Three of Bluegraph's coastal stations belong to the National Ocean Service. The 18 Texas stations named by their water-level numbers belong to the Texas Coastal Ocean Observing Network, and that network's own practices apply there. Bluegraph's tide gauges, which measure the height of the water, have a page of their own.

Bluegraph collects each coastal station's reports from NDBC: wind direction, speed and gust, pressure and its 3-hour change, air temperature and dew point, and whatever else the station measures, such as sea temperature. The wind is shown as measured, at the anemometer's height, not adjusted to 10 m; pressure is shown reduced to sea level. Moss Landing also reports water quality. The stations are on the station list; Compare shows two side by side, and the reference defines each reading.