Sea Window: Marine Weather App with Route Forecasts

The forecast at every waypoint, for the hour you'll be there

Plan a route and set your cruising speed. Sea Window works out when you'll reach each waypoint and pulls the forecast for that spot at that hour, so the whole passage reads as one timeline instead of one forecast for the harbor you leave from.

WindSpeed, gusts and direction in knots, with the apparent wind and your point of sail.
SeasWave height with its period, how comfortable the ride will be, and when seas cross your course.
CurrentThe tidal current you'll meet: with you, against you or setting you sideways.
VisibilityIn nautical miles, so fog on a later leg shows up before you leave the dock.
SpeedChange your planned speed and every arrival time and forecast moves with it.

Route weather for Beaufort to Ocracoke: the start at 03:37 with 7 knots of wind and 0.7 metre seas, and waypoint 2 at 06:18 with 12 knots, 1.0 metre seas, a close-hauled apparent wind and a 1.7 knot cross set

The best times to leave, ranked

The Departure Advisor tries a departure every 30 minutes across the next 72 hours and scores each one for the whole passage, not just the hour you cast off. It checks wind, seas, visibility and squall risk at every waypoint for the time you'd reach it, then groups the good stretches into windows.

72 hoursOne strip for the next three days, each departure colored good, fair or rough for the whole trip.
WindowsWhen each window opens and closes, its best moment, the strongest wind, the highest seas, the lowest visibility and the passage time.
RecommendedThe earliest window within a few points of the best, because there's no reason to wait two days for a forecast that is no better.

When to leave sheet for Beaufort to Ocracoke: two fair windows this morning, and a recommended good window from today 16:07 to Wednesday 03:37 with 16 knots peak wind, 1.3 metre seas and a 10.1 hour passage

The whole marine picture on one screen

The Weather tab puts everything a skipper checks before a trip in one scroll: conditions now, the barometer and where it's heading, fog, squalls, waves, tides and a 7-day outlook, built on the ECMWF, ICON and GFS models.

NowAir and sea temperature, sky and visibility in nautical miles.
WindSpeed, direction and gusts on a compass.
BarometerPressure in hPa on a storm-to-dry dial, and how far it has moved in 3 hours.
Pressure trendA plain-language outlook for the next few hours, including wind shifts and when they arrive.

Weather screen for Newport, Rhode Island: 19 °C and partly cloudy, sea 20.4 °C, 6.6 NM visibility, wind 6.6 knots from the southeast gusting 10.3, barometer steady at 1018 hPa, and a wind shift expected around 16:00

Waves, tides, fog and squalls, read at a glance

These are the cards from the Weather tab, exactly as they appear in the app. Each one answers a question you'd want settled before you leave the dock.

Waves card: sea state 2, slight, 0.8 metres; total 0.8 m every 5 seconds from the south-southwest; swell 0.5 m at 4 seconds; wind wave 0.4 m at 2 seconds from the southwest

Waves and swell

A wave height means little without its period. The waves card splits the sea into its parts, so you can tell a long, easy swell from short, steep chop.

Sea state in a word, next to the total wave height.
The picture rolls with the real wave height, so big seas look big.
Total height with its period and the direction the waves come from.
Swell from distant weather, usually the longer, smoother waves.
Wind wave raised by local wind. A short period feels rougher than the height suggests.

Tides card for Beaufort, Duke Marine Lab, 0.3 NM away, from NOAA CO-OPS on the MLLW datum: rising from 0.1 m to 1.2 m, next high in 6 hours 17 minutes at 10:02, a tide curve for the day, and the next four high and low tides

Tide times for your harbor

The nearest tide station, which way the tide is going, the next turn and the curve for the day. In US waters it reads NOAA stations; elsewhere, a global tide model.

The station and how far away it is, with the data source and the datum heights are measured from.
Rising or falling, and between which heights.
The next high or low: how long until the turn, and when.
The curve for the day, with a line at now and every high and low marked.
The next four highs and lows, with heights and times.

Squall and thunderstorm card with a warning: severe thunderstorm risk, strong convection signals around 04:00, consider postponing or staying in shelter; a 24-hour risk strip, peak CAPE 3460 J/kg, minimum lifted index minus 7.3, peak risk severe

Squall and thunderstorm risk

A thunderstorm can turn an easy passage into a bad afternoon. The squall card reads the convection signals in the forecast and tells you when they peak.

The verdict: how serious it is, when it peaks and what to do about it.
The next 24 hours, hour by hour, from stable in green to severe in red.
The numbers behind it, peak CAPE and the lowest lifted index, if you want the meteorology.

Fog and visibility

Fog is what catches coastal boaters out. The fog card shows when visibility will drop, how far, and what to plan for, across the next 24 hours.

The verdict: how likely fog is, when visibility drops and what to plan for.
The next 24 hours of visibility, hour by hour.
Visibility now, the lowest expected in the next 24 hours, and the peak risk.

Wind and tide, moving on the map

The map shows conditions on the water as they move. Streaks drift with the wind, arrows show the tidal stream, and the wind-speed layer colors the water by strength. Drag the forecast bar to see the next 48 hours.

Wind speedA colored field in knots, with a scale from 0 to 50.
Wind motionAnimated streaks that show direction and strength at a glance.
Tidal streamArrows for the current's set and drift.
Chart layersNOAA nautical charts, OpenSeaMap seamarks, depth shading and depth contours.

Conditions map near Beaufort and Cape Lookout, North Carolina, with the wind-speed layer shading the water from purple near the shore to green offshore, wind streaks, tidal-stream arrows and a forecast bar with a 0 to 50 knot scale

Seven days, hour by hour, and whether the models agree

The 7-day marine forecast lines up wind, weather, air temperature, waves, current and tides for every three hours. A badge on each day says whether GFS, ICON and ECMWF agree, so you know how far to trust a forecast three days out.

WindA chart of wind and gusts across the day, with the peak marked.
WavesHeight, direction and period, with the current's speed and set.
TidesHigh and low times in the same row as the weather.
ConfidenceModels agree, mostly agree or diverge, day by day.

7-day marine forecast for today with a models mostly agree badge, a wind and gust chart peaking at 19 knots, and three-hourly rows of wind, weather, air temperature, waves, current and tide times

Your routes and trips, saved and synced

Save as many routes as you like and check them again whenever the forecast changes. Record a trip to keep its track. Everything syncs to your account, and downloaded map regions and your latest forecasts keep working when the signal drops.

RoutesDistance, waypoints and arrival time at your speed on every card.
TripsThe track you sailed, with distance, duration, and average and top speed.
OfflineDownload map regions. Forecasts, tides and route weather stay on your phone for 24 hours.

Logbook with four saved routes totalling 149 NM, including Beaufort to Ocracoke, 51 NM with 4 waypoints and a 10 hour 8 minute arrival time at 5 knots, and Newport to Edgartown, 43 NM

Questions boaters ask

What is Sea Window?

Sea Window is a marine weather app for iPhone and iPad, built for coastal boaters. It shows the forecast at every waypoint of your route for the time you will reach it, ranks the best times to leave over the next 72 hours, and puts wind, waves, tides, fog, squall risk and a 7-day marine forecast on one screen.

Who is Sea Window for?

Coastal cruising sailors and power cruisers, trawlers included, on trips of four hours to two days: long enough for the weather to change along the way. Anglers and paddlers use it for waves, tides and fog too.

How does route weather work?

Draw a route on the map and set your cruising speed. Sea Window works out your arrival time at every waypoint and fetches the forecast for that place at that hour: wind and gusts, seas and their period, visibility and current.

How does the Departure Advisor pick a window?

It tries a departure every 30 minutes for the next 72 hours. For each one it looks up the wind, seas, visibility and squall risk at every waypoint for when you would reach it, and scores the whole passage from 0 to 100. Runs of good departures become windows, and the earliest window close to the best score is marked Recommended.

Where does the forecast data come from?

Weather and sea data come from the ECMWF, ICON and GFS global models. Tides come from NOAA CO-OPS stations in US waters and from a global tide model everywhere else. Maps come from Mapbox, with NOAA nautical charts, OpenSeaMap seamarks and GEBCO depth contours as map layers.

Does it work outside the US?

Yes. Weather, waves and the conditions map cover the world's coasts. Tides come from NOAA CO-OPS stations in US waters and from a global tide model elsewhere, and the tides card shows the source and the datum its heights are measured from.

What makes Sea Window different from other marine weather apps?

Sea Window plans around your whole trip. It times the forecast to your arrival at each waypoint, scores every departure over the next 72 hours for the entire passage, and shows day by day whether the ECMWF, ICON and GFS models agree. Route weather, departure windows, a full marine forecast and a live conditions map all come in one app.

Can I use knots, feet or Fahrenheit?

Yes. Pick Marine (knots, °C, metres and nautical miles), US (knots, °F, feet and nautical miles) or Metric (km/h, °C, metres and kilometres), or set wind, temperature and heights one by one.

Does it work without a signal?

Download map regions before you go. Your latest forecasts, tides and route weather stay on your phone for 24 hours, so they are there when the signal drops, and they refresh on their own when you are back in range.

Is Sea Window on Android?

Sea Window is for iPhone and iPad. An Android version is planned.

Do I need an account?

Yes. Sign in with Apple, Google or email so your routes, trips and settings follow you between devices. You can delete your account from the app at any time.

Before your next coastal trip

Understand the forecast and compare your options with our marine weather guides.

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