🌤️ Weather Guide

The Beaufort Scale — Force 0 to 12

The Beaufort scale is the universal language of wind at sea. Know these by heart up to Force 8.

Wave heights are significant wave height (average of highest third). Individual waves can be twice this height.

Reading a Marine Forecast

A standard marine forecast gives: area, wind direction and force, sea state, visibility, and sometimes swell. Key points:

• Wind direction is where the wind is coming FROM — a NW wind blows from northwest to southeast.
• Backing / veering: Wind backing = direction rotating anticlockwise (N→W→S). Veering = clockwise (N→E→S). Veering wind often associated with improving weather (in northern hemisphere).
• Synoptic charts: Isobars (lines of equal pressure) — the closer they are, the stronger the wind. Wind flows parallel to isobars, slightly across toward low pressure. Depressions (lows) bring unsettled weather. Highs bring stable, settled conditions.
• Fronts: Cold front = fast wind shift, squalls, clearing afterwards. Warm front = gradual deterioration, rain, reduced visibility. Occluded front = complex, can be the worst of both.
• GRIB numbers: Wind direction and speed are shown as a barb on a stick — the stick tail points into the wind direction, short feather = 5 kn, long feather = 10 kn, pennant = 50 kn.

GRIB Files — What They Are and How to Use Them

GRIB (GRIdded Binary) files are computer model output — raw forecast data in grid format. They show predicted wind, pressure, wave height, rain and more at intervals of 3–6 hours over multiple days. They are NOT a human-issued forecast — a meteorologist has not looked at them — but they are the most detailed tool available for passage planning.

How to read them:

• Use an app: Windy.com (browser and mobile), PredictWind Offshore, Expedition, AvNav, OpenCPN with GRIB plugin.
• Select a weather model: GFS (NOAA, free, global, 3-hourly), ECMWF (European, most accurate for medium range — 4–7 days, subscription required for high resolution), ICON (German, good over Europe), AROME/ARPEGE (French, excellent for Mediterranean short range).
• Compare at least two models. If they agree, confidence is higher. If they disagree significantly, expect uncertainty — be conservative.
• GRIB files degrade beyond 72 hours. Do not plan precise passages based on day 5+ data.

Cloud Reading — The Skipper's Eye

Mediterranean Wind Patterns

The Med has its own wind system. Understanding the dominant winds is essential for planning passages.

Weather Routing Principles for the Mediterranean

• Depart early. Leave at dawn or first light to complete passages before the Meltemi builds to its afternoon maximum. Most passages in the Saronic are 3–6 hours — easily completed by midday if you leave at 0700.
• The 3-day rule. In the Mediterranean, only plan 3 days ahead with confidence. Beyond that, GRIB models diverge significantly. Have a flexible itinerary with Plan B anchorages identified.
• Shelter strategy. Know where you can shelter on any given leg. Identify anchorages to leeward of islands, marinas with reasonable entry in bad weather, and safe spots to wait out a Meltemi.
• Watch the morning sky. If the sky is clear and the wind light at dawn, the afternoon Meltemi is likely to build. If it is already blowing at 0600, it may persist all day — reconsider the passage.
• If in doubt, don't go out. The Med has plenty of places to wait. A missed passage is far preferable to an uncomfortable or dangerous one. Crew morale, safety, and the boat are all worth protecting.
• Head sea vs beam reach. A Meltemi on the nose is exhausting and potentially dangerous. On a beam reach it is exhilarating sailing. Plan routes to have the wind on the beam or behind if possible, rather than bashing into it.

Official Weather Sources — Greece

Pre-departure Weather Checklist

Complete before every passage, ideally the evening before and again first thing in the morning:

• Check wind speed and direction for departure time, noon, and arrival time
• Check GRIB from two different models — do they agree?
• Identify maximum expected wind speed during passage
• Check sea state — note any swell from previous day's wind
• Confirm no fronts or troughs passing within 24 hours of departure
• Check conditions at destination — is entry safe in forecast wind direction?
• Identify a Plan B shelter if conditions deteriorate mid-passage
• Check POSEIDON or EMY for any marine warnings or alerts for your sea area
• Note sunrise / sunset — plan not to arrive at anchor in darkness if avoidable
• Communicate plan to crew — departure time, ETA, what to expect