You forecast for yourself here: chart, barometer and sky first, then the official forecast weighed against the coast.
With my back to the wind, where is the area of low pressure?
On your left and a little ahead, in the northern hemisphere: Buys Ballot's law. Wind blows anticlockwise round a low and clockwise round a high, angled slightly towards the low pressure.
In the north, wind blows anticlockwise round a low and clockwise round a high, angled slightly towards low pressure. Back to the wind, the low is on your left, a little ahead: Buys Ballot's law.
Halve the isobar spacing and the wind doubles. The chart's geostrophic scale reads the wind aloft: at sea take two thirds, more at lower latitudes for the same spacing.
| hPa in 3 h | Tendency |
|---|---|
| Under 1.6 | Slowly |
| 1.6–3.5 | Falling or rising |
| 3.6–6 | Quickly: strong wind coming |
| Over 6 | Very rapidly: gale |
A fast rise blows as hard as a fast fall; an offset error leaves the tendency true.
Will the wind veer or back as a depression passes?
If the centre passes north of you the wind veers, clockwise through S, SW and NW; if it passes south, it backs through SE, E and NE. A frontal low travels along its warm-sector isobars.
A frontal low travels along its warm-sector isobars. If the centre passes north of you the wind veers, clockwise: S, SW, NW. If it passes south, the wind backs: SE, E, NE.
| Stage | Weather | Wind · barometer |
|---|---|---|
| Warm front | Cirrus, halo, lowering cloud, rain | Backs · falls |
| Warm sector | Drizzle, mild, poor visibility | Veers SW · steady |
| Cold front | Squalls, heavy rain | Sharp veer NW · jumps |
| Behind it | Showers, clear air | Gusty NW · rises fast |
When the cold front catches the warm one the low is occluded: it stops deepening and fills. An occlusion brings rain, then a veer and showers. A trough is a weak front; a ridge between lows a brief fair spell, so sail early. A secondary low on the trailing front can deepen fast and outblow its parent.
What does "gale soon" mean in a forecast?
Soon means 6 to 12 hours from the time of issue; imminent is within 6 hours, later over 12. A gale warning for soon, issued at 0600 UTC, means any time from 1200 to 1800 UTC.
NAVTEX: English on 518 kHz, national language on 490; types A, B and D (navigational and weather warnings, search and rescue) cannot be switched off. A SÉCURITÉ call on VHF 16 names a working channel: go there and write it down.
| Term | Means |
|---|---|
| Steadily · rather quickly | 15–25 · 25–35 kn |
| Gale 8 · severe 9 · storm 10 | 34–40 · 41–47 · 48–55 kn |
| Visibility moderate · poor · fog | 2–5 M · 1000 m–2 M · less |
| Sea moderate · rough · very rough | Up to 2.5 · 4 · 6 m |
| Cyclonic | Centre close: big, quick shifts |
| Locally | Straits and capes |
A GRIB is one model's mean wind on a coarse grid: no gusts, no funnelling. Add the coast yourself, plan on the earlier of two models, trust the newest official forecast. A barb points where the wind comes from: long feather 10 kn, short 5.
Why is the sea so steep off a headland when the wind is against the tide?
Wind against tide makes short, steep, breaking seas, worst off headlands at full stream. Round them near slack water and well off, and avoid shoal banks, where seas break as the depth falls to about their height.
Beaufort force is the mean wind (force 7: 28–33 kn); log gusts beside it. Rig load grows as the square of the wind: 24 kn pulls 2¼ times as hard as 16.
Waves grow with wind, fetch and duration: the least sea lies under a weather shore. Forecast heights are significant: the odd wave is nearly twice as high. Swell and wind sea combine as √(swell² + sea²): 2.0 and 1.5 m give 2.5 m. A new long swell announces a distant low.
Wind against tide makes short, steep, breaking seas, worst off headlands at full stream: round near slack water, well off. Seas also break where depth falls to about their height: avoid shoal banks.
When does the sea breeze start and how strong does it get?
On a settled day a sea breeze sets in by late morning, reaches force 3–4 by mid-afternoon, veers a little and dies at dusk. A light offshore wind can hold it off behind a calm belt.
On a settled day a sea breeze sets in by late morning, reaches force 3–4 by mid-afternoon, veers a little and dies at dusk; hot slopes strengthen it (anabatic). A light offshore wind holds it off behind a calm belt. By night a land breeze blows, and off steep slopes a cold katabatic wind, strongest before dawn.
High land bends the wind along straits and round headlands, and speeds it up. A high island casts a wind shadow with a sharp edge, yet in strong winds gusts fall down its lee slopes, hardest at night. Lens-shaped clouds over the peaks warn of them.
When is the best time to sail upwind in the Meltemi?
At dawn, before it builds: the Meltemi blows from the north in the Aegean, under clear skies, at force 6–7 for days, peaking after noon, set up by a Balkan high and a Turkish low.
| Wind | From | Signs |
|---|---|---|
| Meltemi | N, Aegean | Balkan high, Turkish low; clear, 6–7 for days, peak after noon |
| Bora | NE, Adriatic | Cloud cap on the mountains, rising glass; violent gusts |
| Jugo (Sirocco) | SE, Adriatic | Haze, dust, slow build, big sea; may end in Bora |
| Mistral | NW, Gulf of Lion | After a cold front, Genoa low; clear, 7–8 for days |
| Levante | E, Alborán | Funnelled at Gibraltar; long swell |
| Poyraz | NE, Turkey | Cold, strong; with the Dardanelles current |
Make upwind miles at dawn, before a Meltemi builds. Gusts in km/h ÷ 1.852 give knots: 100 km/h is 54 kn.
Will a stronger wind clear sea fog?
No: sea fog is warm moist air over colder water, and wind does not clear it; a sea breeze carries it inshore. Radiation fog, formed over land on clear calm nights, is gone by mid-morning.
Fog forms as air cools to its dew point: a degree apart, fix your position, ready radar and horn. Sea fog is warm moist air over colder water: wind does not clear it; a sea breeze carries it inshore. Radiation fog forms over land on clear calm nights, gone by mid-morning. Frontal fog lifts once the warm front passes.
A thunderstorm throws a cold gust front ahead of its rain: reef first; at anchor, leave room to swing right round. Over high ground they break late in the day. Flash-to-thunder seconds ÷ 3 give kilometres. Stars vanishing to windward: a squall. After a strike, check the through-hulls and hull for leaks first.
Questions from this topic, as the app asks them. Open one to see the answer.
This is the synoptic picture at noon. Where does the wind come from at your position?
A. From about WSW
In the north air circles a low anticlockwise, angled in towards the centre: south of it the wind is about WSW.
You are planning the week from this chart. Where is this low in its life?
A. Occluded and mature — it will slowly fill
When the cold front catches the warm front the low occludes: its deepening is over and it begins to fill.
What wave height do you plan for on the open leg?
A. 2.5 to 4 m
Forecast terms: slight 0.5–1.25 m, moderate 1.25–2.5 m, rough 2.5–4 m, very rough 4–6 m.
You write the wind in the log. What force is it?
D. Force 7 — near gale
Beaufort goes by the mean wind: 28–33 kn is force 7. Log the gusts beside it.
How will the breeze behave through the afternoon?
A. Build to F3–4, veer a little, die at dusk
A sea breeze builds as the land heats, peaks in mid-afternoon, veers through the day in the north and dies at sunset.
You plan the coming days in the Cyclades. What do you expect?
D. Meltemi — N 6–7 under clear skies
High over the Balkans, low over Turkey: the gradient drives the Meltemi, N in the Cyclades, often force 6–7 for days.
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