In a flotilla the lead crew gives you the forecast every morning, but the decision to reef, to wait or to move the boat is still yours. Learn to read a forecast, the barometer and the local winds of the Ionian and the Aegean.
1 · Forecasts
Where the forecast comes from, and which one to trust
Should I plan a sailing day on a weather app or on the official forecast?
On the official forecast from the national met service and its warnings, read on VHF, printed by NAVTEX or posted at the harbour office. Apps show raw model output and miss local effects; when two forecasts disagree, plan on the worse.
Your first source is the lead crew's morning briefing. On your own, the official forecast comes from the national met service: coast stations read it on VHF at set times, NAVTEX prints it aboard, and harbour offices post it. A warning is announced on channel 16 with the word SÉCURITÉ and read out on a working channel: switch to the channel given, listen, then go back to 16.
A phone app shows raw model output and misses local effects. Plan on the official forecast and its warnings; when two forecasts disagree, plan on the worse one.
Forecast says
It means
NW 4 to 5
From the northwest, force 4–5 on the Beaufort scale
Locally 6
Stronger in places: round capes and in channels between islands, where the wind is squeezed
Gusts 25 kn
Short bursts well above the mean wind
2 · Wind strength
Beaufort force, and the gusts on top
At what Beaufort force should I reef a charter yacht?
At force 5, 17–21 knots, reef before you leave; force 4 is full sail and force 7 a day in harbour. Set the sails for the gusts: 15 knots gusting 25 is force 4 with force 6 in it.
Forecasts give the wind as a Beaufort force, named from the mean speed. For a charter yacht with a holiday crew, force 4 is a fine sailing day, force 5 wants a reef, and force 7 is a day in harbour.
Force
Knots
Name
What you do
3
7–10
Gentle breeze
Full sail
4
11–16
Moderate breeze
Full sail, a good day
5
17–21
Fresh breeze
Reef before you leave
6
22–27
Strong breeze
Deep reefs, sheltered legs only
7
28–33
Near gale
Stay in harbour
The force is a mean. Gusts run well above it, and they are what overpowers the boat, so set your sails for the gusts. A forecast of 15 knots gusting 25 is force 4 with force 6 in it. Reef in harbour, where it is easy, not outside in the gusts.
3 · Isobars and barometer
What the pressure tells you
What do closely spaced isobars on a weather chart mean for the wind?
Strong wind: the closer the isobars, the stronger it blows; wide apart, it is light. Aboard, a barometer falling steadily by about 1 hPa an hour says a low is coming and the wind will rise.
A forecast chart joins places of equal pressure with lines called isobars. Read their spacing: packed close, the wind is strong; wide apart, it is light. Under a summer high expect little wind, and allow time and fuel for motoring.
Close togetherstrong wind
Wide apartlight wind, some motoring
Aboard, the barometer gives the trend. One reading means little; write it down every few hours. A steady fall of about 1 hPa an hour, with high cloud thickening, says a low is on its way and the wind will rise.
Rule
Close isobars, strong wind. Falling barometer, rising wind.
4 · Local winds
What the land does to the wind
Why does a calm lunch anchorage off a beach turn into a lee shore?
A sea breeze: on a hot settled day the land heats up and draws wind in from the sea from around midday until evening. It blows onshore, so the beach you anchored off becomes a lee shore.
On a hot settled day the land heats up and draws in a sea breeze from around midday until evening. It blows onshore, so a calm lunch stop off a beach becomes a lee shore. The Ionian's summer northwesterly keeps the same clock: a calm morning, a breeze building from late morning to about force 4, gone around sunset.
High land makes its own wind. At night cold air pours down the valleys in hard gusts, so anchor well clear of a valley mouth.
A wind shift can open your bay to the sea. The wind veers when it shifts clockwise, south to west for example, and backs when it shifts anticlockwise. Before dark, ask where tonight's wind will come from, and move if the bay will be open to it.
5 · Meltemi
The Aegean's summer northerly
What time of day is best for sailing in the Meltemi?
Early morning, when the Meltemi is lightest: leave at first light and be in by midday, as the afternoon often brings force 6–7. It often blows for days, so do not count on it dying overnight.
The Meltemi blows over the Aegean in summer, hardest in July and August: from the northeast in the north, from the north in the Cyclades, from the northwest in the Dodecanese. It is a fair-weather wind. The sky is clear and the barometer steady while it blows force 6 to 7, so the sky gives no warning. Only the forecast does.
When
What to expect
Early morning
Lightest: the time to make your miles
Afternoon
Strongest, often force 6–7
The days after
More of the same: it often blows for days on end
If a leg must be made, leave at first light and be in by midday. Do not count on it blowing itself out overnight: plan on the forecast, keep to sheltered legs or stay put, and ask the lead crew for a route.
6 · Go or no-go
Deciding whether to sail
How do I decide whether to sail today or stay in harbour?
Make a go or no-go check: the wind with its gusts, its direction (upwind is slower and wetter), the hours the leg takes and what your crew can stand. If the answer is doubtful, stay in harbour.
The forecast is half of the decision; your boat and crew are the other half. Weigh the wind with its gusts, its direction (upwind is slower, wetter and harder), the hours the leg will take and what your crew can stand. A leg to windward takes far longer than its miles suggest: you tack, and the sea slows you. If the answer is doubtful, stay: nobody regrets a day in harbour.
Go or no-go?
Force and gusts: within your limit?
Upwind or downwind? How many hours?
Crew: rested, experienced, willing?
Shelter on the way if it gets worse?
Thunderstorms are the exception to a quiet forecast. A tall dark cloud building over the land in the afternoon, then thunder, means a sudden violent squall. Reef or drop the sails before it reaches you, not when it hits.
Remember
Reduce sail before the wind arrives. If you wonder whether to reef, reef.
Practice questions
Questions from this topic, as the app asks them. Open one to see the answer.
Two forecasts for tomorrow
Phone app: W 3, sunny
National met service: NW 6, locally 7
NAVTEX: warning, NW 7 in your area
Your crew prefers the phone app. Which forecast do you plan on?
The app, unless the barometer starts to fall
The app — it is more detailed for your spot
The official one — plan for force 6–7
An average of the two — plan for force 5
Show the answer
C. The official one — plan for force 6–7
Plan on the official forecast and warnings, and on the worse of two forecasts that disagree.
All 20 questions of this topic are in the app: practice by topic with the reason after every answer, your mistakes brought back, and a timed mock exam. Free, no sign-up, in the browser or in Telegram.
