Halyard - offshore marine weather

Seven day outlook · waypoint · updated 11:42 UTC

The week ahead, one line per day, nothing hidden behind a tap.

Daily values are the 06:00 to 18:00 window. Gusts are the 95th percentile across the three models, so a quiet number here is a number you can plan on.

Day	Wind	Gust	Direction	Sig. wave	Period	Pressure	Rain	Visibility	Status
Wed 9today	24 kn	31	248°	2.8 m	9 s	1004 falling	3.2 mm	4 nm	gale 8
Thu 10	17 kn	23	301°	2.1 m	10 s	1012 rising	0.4 mm	9 nm	moderating
Fri 11	12 kn	16	318°	1.6 m	11 s	1019 steady	0.0 mm	12 nm	fair
Sat 12	9 kn	13	352°	1.2 m	12 s	1023 steady	0.0 mm	15 nm	fair
Sun 13	13 kn	18	216°	1.4 m	8 s	1018 falling	1.1 mm	10 nm	backing
Mon 14	20 kn	27	231°	2.4 m	8 s	1008 falling	6.8 mm	5 nm	strong 6
Tue 15	22 kn	29	265°	2.9 m	9 s	1003 falling	4.5 mm	4 nm	near gale 7

Tides and the area forecast

The tide table for the port you are actually heading to.

Set a destination and Halyard pulls the harmonic prediction for the nearest standard port, then corrects it with the pressure you are seeing on deck.

Brest, standard port

Wed 09 Sep · coefficient 94 · datum chart datum

00:0006:0012:0018:0024:00

high water02:14 UTC6.6 m
low water08:29 UTC1.2 m
high water14:37 UTC6.9 m
low water20:53 UTC0.9 m
Thu high water02:58 UTC6.7 m
Thu low water09:12 UTC1.1 m

Surge correction applied: -0.18 m for 1004 hPa. Chenal du Four stream turns north-going at 12:05 UTC, peak 3.1 kn at 15:10.

Area forecast, Biscay and Fitzroy

Issued 09:00 UTC · valid to Wed 21:00 UTC

Gale warning. Southwesterly 6 to gale 8, veering northwesterly and decreasing 4 or 5 by early Thursday. Sea state rough, occasionally very rough in the west at first, becoming moderate. Rain then showers. Visibility moderate or poor, becoming good.

Low 988 hPa near 52°N 014°W moving northeast and filling slowly. Ridge 1024 hPa building from the southwest by Friday and holding through the weekend. Next depression expected Sunday night, deepening to 1003 hPa by Tuesday.

Departure window from Camaret, next 48 h 3 h blocks

Wed 12:00Thu 00:00Thu 12:00Fri 00:00Fri 12:00

Thu 00:00Wind northwest 18 kn falling to 12 kn, seas 2.1 m easing to 1.6 m by 06:00. Stream fair through the Raz de Sein from 04:40 UTC. Thu 12:00Brief freshening to 22 kn on the back edge of the front, then the ridge. Best long window opens after 15:00.

Where the numbers come from

Three models, one hundred and twenty seven sensors, and no averaging that hides a gust.

When the models disagree we show you the disagreement. The board carries the spread, not just the mean, so you can see when a forecast is confident and when it is guessing.

6min

Refresh cadence for wind, pressure and wave once a new run is ingested.

0.1deg

Ocean grid from ECMWF, sharpened to 0.025° within 30 nm of the coast.

127

Buoys, lightships and coastal stations feeding the nowcast layer.

14days

Forecast horizon, with spread shown from day four onwards.

Global GFS 0.25° and ECMWF IFS 0.1°

Four runs a day. Pressure fields drive the low and ridge tracking on the board; wind is bias-corrected against the buoy network every cycle.

Coastal Arome 0.025° and Harmonie

High-resolution layers for the Channel, Biscay, the Irish Sea and the Baltic. These catch the land breeze and headland acceleration the globals smooth away.

Observed Buoys, satellite scatterometer, AIS weather reports

Every reading within 60 nm of your waypoint is plotted with its age. A number older than 90 minutes is greyed, never quietly dropped.

Beyond phone signal

The whole board in an 18 kB email, built for Iridium.

Send a one-line request from any satellite mailer and Halyard replies with a compressed packet: a 48 hour wind and wave grid around your position, the tide table for your destination, and the area forecast as text. The app renders it offline.

Works with Iridium Go, Starlink and Inmarsat mailers. Plain text in, plain text out, no attachment blocking.
Choose your resolution. 0.5° for a quick look at 6 kB, 0.1° for a routing decision at 18 kB.
Positions from your log. Reply to a packet and the next one is centred on where you are now.

// to: board@halyard.sea · subject: any grib 47.2N 8.7W radius 120nm res 0.1 hours 48 step 3 layers wind,gust,press,wave tide brest days 3 text biscay,fitzroy // reply, 11:44 UTC, 17.6 kB // run 09 Sep 06Z · 17 x 17 cells · 17 steps · 4 layers // tide brest 3 days · text 2 areas · next run 12Z at 14:05 // wind max in packet: 33 kn at 12Z +09 h, 47.6N 9.4W

Plans

Free at the pontoon. Paid where it matters.

Coastal covers day sailing and the tide table. Offshore adds the satellite packet and the model spread. Race adds polars and routing for a whole crew.

Coastal

0EUR / month

Live board for one waypoint
Tide tables for 1,400 ports
Three day outlook
Area forecasts and warnings

Start with Coastal

Offshore · most skippers

12EUR / month

Everything in Coastal
Satellite email packets, unlimited
Fourteen day outlook with model spread
Departure windows and stream timing
Offline rendering on two devices

Start Offshore

Race

39EUR / month

Everything in Offshore
Polar upload and isochrone routing
Ensemble tracks, 51 members
Crew seats, up to eight
Shore team shared board

Talk to us about Race

"We left Camaret on the window Halyard drew, four hours after the harbour office told us to wait a day. The pressure trend was right and the office was cautious. We had the Raz with the stream and a flat sea by dawn."

Maren Kjeldsen Skipper, Ondine, 40 ft · Brest to Baiona, September 2025 Logged 612 nm on Offshore, 11 satellite packets