Marine Forecast

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name: marine-forecast description: "Marine and sailing weather via Open-Meteo. Waves, swell, sea temperature, wind, tides, ocean currents, and sailing assessments. Free, no API key, global coverage." homepage: https://open-meteo.com/en/docs/marine-weather-api metadata: {"clawdbot":{"emoji":"🌊","requires":{"bins":["curl"]}}}

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Marine Forecast

Marine and sailing weather using Open-Meteo Marine API + Weather API. Free, no API key required, works worldwide.

Two APIs are used together — replace LAT, LON, and TZ in all commands:

Marine API (marine-api.open-meteo.com) — waves, swell, sea temp, currents, tides

Weather API (api.open-meteo.com) — wind, gusts, air temp, pressure, visibility

Find coordinates for any location using web search or the user's input. Use the nearest timezone (IANA format, e.g. Europe/London, America/New_York, Atlantic/Canary).

Current conditions

Sea state:

curl -s "https://marine-api.open-meteo.com/v1/marine?latitude=LAT&longitude=LON¤t=wave_height,wave_direction,wave_period,swell_wave_height,swell_wave_direction,swell_wave_period,sea_surface_temperature&timezone=TZ"

Wind and atmosphere:

curl -s "https://api.open-meteo.com/v1/forecast?latitude=LAT&longitude=LON¤t=temperature_2m,wind_speed_10m,wind_direction_10m,wind_gusts_10m,apparent_temperature,pressure_msl,cloud_cover,visibility&timezone=TZ"

Run both and combine the results into a single briefing.

Hourly forecast

Marine (up to 16 days, adjust forecast_days):

curl -s "https://marine-api.open-meteo.com/v1/marine?latitude=LAT&longitude=LON&hourly=wave_height,wave_direction,wave_period,swell_wave_height,swell_wave_direction,swell_wave_period,swell_wave_peak_period,wind_wave_height,wind_wave_direction,sea_surface_temperature,ocean_current_velocity,ocean_current_direction,sea_level_height_msl&forecast_days=3&timezone=TZ"

Wind (up to 16 days):

curl -s "https://api.open-meteo.com/v1/forecast?latitude=LAT&longitude=LON&hourly=wind_speed_10m,wind_direction_10m,wind_gusts_10m,temperature_2m,pressure_msl,visibility,cloud_cover,precipitation_probability&forecast_days=3&timezone=TZ"

Daily summary

Marine:

curl -s "https://marine-api.open-meteo.com/v1/marine?latitude=LAT&longitude=LON&daily=wave_height_max,wave_direction_dominant,wave_period_max,swell_wave_height_max,swell_wave_direction_dominant,swell_wave_period_max&forecast_days=7&timezone=TZ"

Weather:

curl -s "https://api.open-meteo.com/v1/forecast?latitude=LAT&longitude=LON&daily=wind_speed_10m_max,wind_gusts_10m_max,wind_direction_10m_dominant,temperature_2m_max,temperature_2m_min,sunrise,sunset,uv_index_max,precipitation_probability_max&forecast_days=7&timezone=TZ"

Tides (sea level)

curl -s "https://marine-api.open-meteo.com/v1/marine?latitude=LAT&longitude=LON&hourly=sea_level_height_msl&forecast_days=3&timezone=TZ"

High/low tide: find local maxima and minima in the sea_level_height_msl array. Sea level includes tidal signal + inverted barometer effect.

Ocean currents

curl -s "https://marine-api.open-meteo.com/v1/marine?latitude=LAT&longitude=LON&hourly=ocean_current_velocity,ocean_current_direction&forecast_days=3&timezone=TZ"

Presenting results

Always present marine data as a structured sailing briefing:

Current conditions format

Sea:    [wave_height]m waves, [wave_period]s period, from [direction]
Swell:  [swell_wave_height]m from [direction], [swell_wave_period]s period
Wind:   [wind_speed] km/h [direction], gusts [wind_gusts] km/h
Temp:   Air [temperature]C (feels [apparent_temperature]C), Sea [sea_surface_temperature]C
Sky:    [cloud_cover]% cloud, [visibility/1000]km visibility

Sailing assessment

Rate conditions based on the data:

Calm — waves < 0.5m, wind < 12 km/h (Beaufort 0-2)

Light — waves 0.5-1m, wind 12-19 km/h (Beaufort 3)

Moderate — waves 1-2m, wind 20-38 km/h (Beaufort 4-5)

Rough — waves 2-3m, wind 39-49 km/h (Beaufort 6)

Very Rough — waves 3-4m, wind 50-61 km/h (Beaufort 7)

Dangerous — waves > 4m or wind > 62 km/h (Beaufort 8+)

Flag warnings:

Small craft advisory: wind gusts > 50 km/h or wave height > 3m

Gale warning: sustained wind > 62 km/h or wave height > 5m

Suggest activity suitability: sailing, diving, fishing, swimming, surfing

Beaufort scale

| Force | km/h | Description | Sea State | |-------|------|-------------|-----------| | 0 | 0-1 | Calm | Flat | | 1 | 2-5 | Light air | Ripples | | 2 | 6-11 | Light breeze | Small wavelets | | 3 | 12-19 | Gentle breeze | Large wavelets | | 4 | 20-28 | Moderate breeze | Small waves | | 5 | 29-38 | Fresh breeze | Moderate waves | | 6 | 39-49 | Strong breeze | Large waves | | 7 | 50-61 | Near gale | Breaking waves | | 8 | 62-74 | Gale | High waves | | 9 | 75-88 | Severe gale | Very high waves | | 10 | 89-102 | Storm | Exceptionally high waves |

Wind direction conversion

Convert degrees to compass: divide by 22.5, round, index into [N, NNE, NE, ENE, E, ESE, SE, SSE, S, SSW, SW, WSW, W, WNW, NW, NNW].

Quick reference: 0=N, 45=NE, 90=E, 135=SE, 180=S, 225=SW, 270=W, 315=NW.

Units

| Measurement | Unit | |-------------|------| | Wave height | meters (m) | | Wave period | seconds (s) | | Wind speed | km/h | | Temperature | Celsius (C) | | Current velocity | km/h | | Directions | degrees (0=N, 90=E, 180=S, 270=W) | | Sea level | meters relative to MSL | | Visibility | meters | | Pressure | hPa |

Users may prefer knots for wind. Convert: knots = km/h * 0.539957. Add &wind_speed_unit=kn to the weather API URL to get knots directly.

Popular sailing locations (reference)

| Region | Example | Lat | Lon | |--------|---------|-----|-----| | Canary Islands | Las Palmas | 28.1 | -15.4 | | Balearics | Palma de Mallorca | 39.57 | 2.65 | | Greek Islands | Piraeus | 37.94 | 23.65 | | Croatia | Split | 43.51 | 16.44 | | Caribbean | St. Maarten | 18.04 | -63.05 | | South Pacific | Tahiti | -17.53 | -149.57 | | Southeast Asia | Phuket | 7.88 | 98.39 | | East Africa | Zanzibar | -6.16 | 39.19 | | Australia | Sydney | -33.87 | 151.21 | | US East Coast | Annapolis | 38.97 | -76.49 | | UK | Solent | 50.77 | -1.30 | | Scandinavia | Gothenburg | 57.71 | 11.97 |

Data sources

ECMWF WAM (European Centre for Medium-Range Weather Forecasts)

NOAA GFS Wave (Global Forecast System)

DWD GWAM/EWAM (German Weather Service)

Resolution: 5-25 km depending on region and model

Updates: multiple times per day

Forecast range: up to 16 days (forecast_days=16)

Notes

All data is JSON. Parse with jq if available, otherwise read raw JSON.

Hourly data returns large arrays. For quick checks, use current parameters. For planning, use daily. Use hourly only when the user needs detailed breakdowns.

Combine marine + weather API calls to give a complete picture. Neither alone is sufficient for a full sailing briefing.

Sea level data approximates tides but does not label high/low explicitly. Derive from local maxima/minima in the hourly array.

For coastal areas, data accuracy depends on proximity to the nearest grid point. Open ocean coverage is excellent; harbors and bays may be less precise.

Docs: https://open-meteo.com/en/docs/marine-weather-api

All data is JSON. Parse with jq if available, otherwise read raw JSON.

Hourly data returns large arrays. For quick checks, use current parameters. For planning, use daily. Use hourly only when the user needs detailed breakdowns.

Combine marine + weather API calls to give a complete picture. Neither alone is sufficient for a full sailing briefing.

Sea level data approximates tides but does not label high/low explicitly. Derive from local maxima/minima in the hourly array.

For coastal areas, data accuracy depends on proximity to the nearest grid point. Open ocean coverage is excellent; harbors and bays may be less precise.

Docs: https://open-meteo.com/en/docs/marine-weather-api