NOAA Buoy Data Metric Definitions

Sea surface temperature measured at or near the water surface, typically at a depth of 0.5-1.5 meters. This is one of the most widely used oceanographic measurements, critical for understanding marine ecosystems, weather patterns, and climate trends.

Units

°C (metric) / °F (imperial)

Range

-2 to 35°C (28 to 95°F)

Importance

Fundamental indicator of ocean health, marine habitat conditions, and weather system development. Anomalies signal El Niño/La Niña events.

Applications

Marine biology, fisheries management, hurricane forecasting, surf wetsuit selection, coral reef monitoring

Atmospheric temperature measured at the station's anemometer height, usually 4-5 meters above sea level. Provides context for sea-air heat exchange and local weather conditions.

Units

°C (metric) / °F (imperial)

Range

-20 to 40°C (-4 to 104°F)

Importance

Key for understanding fog formation, thermal gradients, and marine layer dynamics along coastlines.

Applications

Coastal weather forecasting, marine navigation, sailing conditions, offshore operations

The average height of the highest one-third of all waves during the measurement period. This statistically defined value best represents what an observer would estimate as the "wave height" when looking at the sea surface.

Units

m (metric) / ft (imperial)

Range

0.1 to 15m (0.3 to 49ft)

Importance

The most widely referenced wave measurement. Directly impacts vessel safety, coastal flooding risk, and surf conditions.

Applications

Marine safety warnings, surf forecasting, coastal engineering, offshore platform design, shipping route planning

Height of the swell component of waves, which are generated by distant storms and travel long distances across the ocean. Swell is characterized by longer periods and more uniform wave trains compared to local wind waves.

Units

m (metric) / ft (imperial)

Range

0 to 10m (0 to 33ft)

Importance

Indicates incoming energy from distant storm systems. Critical for distinguishing between local chop and long-period ocean swell.

Applications

Surf forecasting, coastal erosion prediction, harbor operations, maritime navigation

Height of waves generated by local wind conditions, as opposed to swell arriving from distant storms. Wind waves are typically shorter in period and more chaotic in appearance.

Units

m (metric) / ft (imperial)

Range

0 to 6m (0 to 20ft)

Importance

Separating wind sea from swell helps mariners understand current conditions versus incoming energy.

Applications

Small craft advisories, fishing conditions, harbor entrance safety, oil platform operations

The single highest wave recorded during the measurement period, typically 20-40 minutes. Can be significantly larger than significant wave height due to wave interference and statistical extremes.

Units

m (metric) / ft (imperial)

Range

0.2 to 25m (0.7 to 82ft)

Importance

Critical safety metric. The maximum wave represents the actual worst-case impact force for vessels and structures.

Applications

Vessel design criteria, offshore platform engineering, maritime safety, rogue wave research

The period (time between successive wave crests) associated with the most energetic waves in the spectrum. Longer periods indicate swell from distant storms; shorter periods indicate locally generated wind waves.

Units

s (metric) / s (imperial)

Range

3 to 22 seconds

Importance

Combined with wave height, period determines wave energy and breaking characteristics. A 2m wave at 18s carries vastly more energy than a 2m wave at 6s.

Applications

Surf quality assessment, coastal erosion forecasting, wave energy harvesting, vessel motion prediction

The average period of all waves in the spectrum, weighted equally regardless of energy. Provides a broader characterization of the overall sea state than dominant period alone.

Units

s (metric) / s (imperial)

Range

3 to 15 seconds

Importance

Useful for understanding mixed sea states where multiple wave systems overlap. A low average with high dominant period suggests one clean swell amid chop.

Applications

Vessel response modeling, comfort predictions, sea state classification

The period of the swell component specifically, representing the time between crests of long-distance traveling waves. Longer swell periods travel faster and arrive from more distant storms.

Units

s (metric) / s (imperial)

Range

6 to 25 seconds

Importance

Long-period swells (>15s) originate from powerful distant storms and can cause significant coastal impacts even with modest heights.

Applications

Surf forecasting, harbor resonance prediction, coastal flooding warnings, wave setup calculations

The compass direction from which the dominant waves are approaching. Measured in degrees true, where 0°/360° is north, 90° is east, 180° is south, and 270° is west.

Units

° true (metric) / ° true (imperial)

Range

0 to 360°

Importance

Determines which coastlines receive wave energy. Combined with local bathymetry, direction controls wave focusing, refraction, and breaking patterns.

Applications

Surf spot forecasting, coastal erosion assessment, harbor wave protection, navigation route planning

The compass direction from which swell waves are approaching. Since swell can travel thousands of miles, this direction indicates the bearing toward the originating storm system.

Units

° true (metric) / ° true (imperial)

Range

0 to 360°

Importance

Tracks the origin of incoming swell energy. Shifts in swell direction signal new storm systems or changing weather patterns.

Applications

Storm tracking, multi-swell identification, coastal exposure analysis

The compass direction from which locally generated wind waves are approaching. Typically aligns closely with the current wind direction.

Units

° true (metric) / ° true (imperial)

Range

0 to 360°

Importance

Helps distinguish between local sea conditions and distant swell. Crossed wind-wave and swell directions create confused, dangerous seas.

Applications

Maritime safety, crossed seas detection, fishing conditions, small vessel advisories

Sustained wind speed averaged over 8 minutes (NOAA standard), measured at anemometer height, typically 4-5 meters above sea level. Reported as the scalar mean of the wind velocity.

Units

m/s (metric) / kts (imperial)

Range

0 to 40 m/s (0 to 78 kts)

Importance

Primary driver of local wave generation and a key safety parameter for all maritime operations.

Applications

Marine weather warnings, sailing conditions, wave generation models, offshore wind energy assessment

The compass direction from which the wind is blowing, measured in degrees true. Determined from vector-averaged wind components over the measurement period.

Units

° true (metric) / ° true (imperial)

Range

0 to 360°

Importance

Determines fetch length for wave generation, coastal exposure, and upwelling/downwelling patterns that affect marine ecosystems.

Applications

Weather routing, wave forecasting, upwelling prediction, fire weather, sailing strategy

The peak 5-second sustained wind speed during the measurement period. Gusts can exceed sustained wind speed by 30-50% and represent the maximum wind force experienced.

Units

m/s (metric) / kts (imperial)

Range

0 to 60 m/s (0 to 117 kts)

Importance

Critical safety metric. Structural loads and vessel knockdown risk are driven by gust speed, not sustained wind.

Applications

Small craft warnings, offshore crane operations, bridge closures, structural engineering, kite/wing sports

The compass direction associated with the peak wind gust. May differ from mean wind direction during turbulent or shifting wind conditions.

Units

° true (metric) / ° true (imperial)

Range

0 to 360°

Importance

Important for understanding wind variability and turbulence. Large deviations from mean direction indicate unstable atmospheric conditions.

Applications

Aviation operations, vessel handling, atmospheric turbulence assessment

Atmospheric pressure at sea level, measured in hectopascals (millibars). Pressure changes indicate passing weather systems: falling pressure signals approaching storms, rising pressure indicates clearing conditions.

Units

hPa (metric) / inHg (imperial)

Range

960 to 1050 hPa (28.3 to 31.0 inHg)

Importance

The most fundamental weather observation. Rapid pressure drops are the hallmark of intensifying storms and cyclones.

Applications

Storm tracking, weather forecasting, barometric tide corrections, altimeter calibration

Horizontal visibility distance, typically measured by optical sensors. Reduced visibility at sea can result from fog, rain, haze, sea spray, or blowing sand.

Units

km (metric) / nmi (imperial)

Range

0 to 30+ km (0 to 16+ nmi)

Importance

Direct safety concern for navigation. Fog and reduced visibility are among the leading causes of maritime collisions.

Applications

Maritime navigation safety, fog warnings, vessel traffic management, offshore helicopter operations

The ratio of actual water vapor to the maximum amount the air can hold at its current temperature. High humidity over warm water promotes convective storm development.

Units

% (metric) / % (imperial)

Range

30 to 100%

Importance

Affects fog formation, evaporation rates, and human comfort. Near 100% values often coincide with fog or precipitation.

Applications

Fog prediction, evaporation modeling, corrosion assessment, HVAC design for marine structures

The temperature to which air must be cooled to reach saturation (100% relative humidity). When air temperature approaches dewpoint, fog or condensation forms.

Units

°C (metric) / °F (imperial)

Range

-20 to 30°C (-4 to 86°F)

Importance

Best single indicator of moisture content. The temperature-dewpoint spread (depression) directly predicts fog likelihood.

Applications

Fog forecasting, marine layer prediction, icing risk assessment, comfort index calculation

The ratio of wave height to wavelength, indicating how "steep" waves are. As steepness increases, waves become more likely to break and pose greater danger to vessels.

Units

ratio (metric) / ratio (imperial)

Range

0.001 to 0.100

Importance

Steepness above 1/7 (0.142) causes waves to break. Even lower values (>0.04) indicate dangerous conditions for small vessels.

Applications

Maritime safety assessment, vessel stability analysis, breaking wave prediction, coastal hazard warnings

First-order mean wave direction from spectral analysis. Derived from the first Fourier coefficient of the directional wave spectrum at each frequency.

Units

° (metric) / ° (imperial)

Range

0 to 360°

Importance

Provides frequency-dependent directional information that reveals multiple wave systems invisible in bulk statistics.

Applications

Directional spectrum analysis, wave model validation, multi-modal sea state characterization

Second-order mean wave direction from spectral analysis. Derived from the second Fourier coefficient, providing additional directional resolution.

Units

° (metric) / ° (imperial)

Range

0 to 360°

Importance

Together with Alpha1, enables reconstruction of the full directional wave spectrum at each frequency.

Applications

Advanced wave modeling, directional spreading estimation, wave energy converter design

First normalized polar coordinate of the Fourier coefficients, representing directional concentration. Values near 1.0 indicate highly directional (focused) wave energy; values near 0 indicate broadly spread energy.

Units

unitless (metric) / unitless (imperial)

Range

0 to 1.0

Importance

Quantifies how focused the wave energy is in direction. Low R1 values indicate confused seas with energy arriving from many directions.

Applications

Crossed seas detection, wave focusing analysis, harbor resonance studies, wave energy device siting

Second normalized polar coordinate of the Fourier coefficients, providing higher-order directional resolution. Helps distinguish between single-peaked and double-peaked directional distributions.

Units

unitless (metric) / unitless (imperial)

Range

0 to 1.0

Importance

Low R2 with high R1 suggests a clean single wave system. Both low indicates chaotic multi-directional seas.

Applications

Wave system identification, spectral partitioning validation, offshore structure response analysis

Distribution of wave energy across different frequencies (periods). The spectral density function S(f) describes how wave energy is partitioned, with peaks corresponding to distinct wave systems (swell, wind sea).

Units

m²/Hz (metric) / m²/Hz (imperial)

Range

0 to 100+ m²/Hz

Importance

The fundamental representation of the sea state. Contains far more information than bulk statistics like significant wave height.

Applications

Wave model validation, wave energy resource assessment, structural fatigue analysis, spectral partitioning, oceanographic research