Systems and forecasts
In temperate latitudes the weather is dominated by depressions — areas of low pressure — that track roughly eastward bringing their warm and cold fronts, separated by ridges of higher pressure that bring settled spells. Wind blows nearly along the isobars, anticlockwise around a low in the northern hemisphere, and harder where the isobars are close together. The skipper builds the picture from the shipping forecast, the inshore-waters forecast, NAVTEX and coastal-station reports, and reads the synoptic chart to see what is coming rather than only what is here.
| Feature | Typical weather |
|---|---|
| Warm front approaching | Lowering cloud, continuous rain, wind backing then veering |
| Cold front passing | Squally showers, a sharp veer, rising pressure, then clearing |
| Tight isobars | Strong winds |
| Ridge / high pressure | Lighter winds, settled, risk of fog or a sea breeze |
| Reading the synoptic picture. |
Local effects and sea state
On top of the large-scale systems, coastal effects matter: sea breezes that build on a sunny afternoon, land breezes at night, and the acceleration of wind around headlands. The sea state depends on wind strength, its duration and its fetch, and — critically — on the tide: wind against tide raises a short, steep and dangerous sea even in a moderate breeze. The skipper reads the Beaufort scale by the state of the sea and plans to avoid the worst combinations.
TIP — Watch the barometer's trend A steadily falling barometer warns of a deepening low and strengthening wind before the wind itself arrives. The trend matters more than the value; a rapid fall deserves an early rethink of the plan.
WARNING — Wind over tide is the coastal trap When wind blows against the tidal stream the sea becomes short, steep and dangerous out of all proportion to the wind strength. Know where and when it happens on your route and plan around it.