The Meltemi

The northerly wind that decides an Aegean charter week — when it blows, where it blows hardest, and how to plan a week around it.

Reviewed by Adrian Sneed, Charter Broker at Sneed Charters — a family brokerage arranging crewed yacht charters in the Mediterranean since 1992.

What it is, and what causes it

Sailors say meltemi; meteorologists say Etesians, from the Greek etos, “year” — a wind that returns annually. The word meltemi is probably a loan from the Italian mal tempo, bad weather, though the etymology is not settled.

You will often read that the meltemi forms where an extension of the Azores high meets the Asian monsoon low. That explanation is wrong, and the leading peer-reviewed study says so directly: Tyrlis, Lelieveld and Steil found that a trough separates the Azores and central European anticyclones, so the Azores high is not the relevant one.

What actually drives it is a pressure dipole between the Anatolian thermal low — an extension of the Asian heat low — and high pressure over central Europe and the western Mediterranean. South Asian monsoon heating forces westward-propagating Rossby waves that build an upper-level ridge over the eastern Mediterranean; a wave disturbance arriving from the North Atlantic triggers ridge development over the Balkans; and subsidence under clear skies then strengthens and anchors that ridge. That last step is why episodes persist longer than ordinary synoptic weather.

When it blows, and how reliably

The season runs roughly 15 May to 15 October, with the core in June to September and the peak from mid-July to mid-August. The documented maximum falls in the first week of August — which is also the single most crowded fortnight in the European tourism calendar.

For how often it actually blows hard, the most useful public record is the National Observatory of Athens station at Tinos, running since 2009, which counts days with a maximum gust of 50 km/h or more.

Across the record, the July–August count has ranged from 20 days (2014) to 47 (2016). In each of the last three years it has run at roughly 60% of the days in June, July and August combined. And that threshold is gusts above 50 km/h — lighter meltemi days are additional.

Episodes usually last under seven or eight days, with a cluster in the four-to-eight-day range. Some run far longer: the Tinos record shows 18 consecutive days of strong meltemi from 30 July to 16 August 2026.

How hard it blows

In the broad reanalysis, the commonest wind speed during an Etesian regime is 5–6 m/s — around 10 to 12 knots. That is the average across a large area, and it is not what a boat in the Cyclades corridor feels in a strong episode. In those, speeds regularly exceed 15 m/s (about 29 knots, force 7), with gusts of 20–25 m/s (39–49 knots, force 8–9). Fifty-year return levels across Aegean stations run from 21 to 33 m/s.

On 30 July 2026 the Tinos station recorded a gust of 82 km/h (44 knots), the strongest summer gust in its eighteen-year history.

The daily cycle, and a correction worth making

The meltemi has a real daily rhythm: it is lightest around midnight, begins strengthening from early morning, and peaks in the early afternoon as the Anatolian thermal low deepens under the day’s heating. It eases after sunset.

What you will often be told — that it dies away at night — is misleading once an episode is established. Over the Cyclades the diurnal range is only a little over 2 m/s, roughly four knots. A force 8 afternoon does not become a calm night; it becomes a slightly less windy one. The practical consequence is real: long legs are worth starting at dawn, but do not plan a week on the assumption that the wind switches off after dinner.

Where it blows hardest

The wind backs and veers as you move through the Aegean — north-easterly in the north, northerly in the centre, north-westerly in the south and south-east.

Crete changes the picture east of it. The island’s mountains decelerate the flow as much as 120 km upstream, and the reduced Coriolis effect in that deceleration zone deflects the wind eastward — producing winds around 8 m/s stronger east of Crete than they would otherwise be, with the strongest between Crete and Karpathos. This is blocking and deflection rather than simple funnelling.

Two things we are not going to tell you, because we could not verify them. Charter guides routinely describe venturi acceleration in the Kea–Kythnos and Paros–Naxos channels. The Kafireas Strait is genuinely one of the windiest places in Greece, but no source we could find establishes the venturi mechanism for it either, and one regional study found no straits or channels standing out as local maxima at all. The winds are real; the tidy explanation may not be.

What about the Saronic and the Ionian?

The Saronic Gulf is usually described as sheltered. We could find no meteorological study that establishes that. What we can point to is operational evidence, which is arguably better: on each of the three biggest recent meltemi shutdowns — 8 August 2025, 19 September 2025 and 14 August 2026 — sailings from Rafina and Lavrio to the Cyclades were banned while Saronic Gulf services ran normally. That is a narrower claim than “sheltered”, and it is one you can rely on.

The Ionian is often called “outside the meltemi”. It is not; it is weaker. Twenty-year return levels there are 23 m/s against 25 m/s in the Aegean. For a family week in August that difference matters enormously. It is still not a millpond.

What it does to the ferries — and to your week

The clearest measure of a meltemi episode is when the port authorities stop the ferries. There is no published statutory Beaufort threshold; in practice conventional ferries stop around 8 Beaufort and fast craft rather earlier, with the decision resting with the master and the local port authority.

Note the September date. The meltemi is not finished when the school holidays are.

How we plan around it

• For July and August with non-sailors aboard, we book the Ionian or the Saronic, not the Cyclades. You lose the Mykonos photograph. You keep the week.
• In the Cyclades we set the direction from the forecast, not the itinerary. The same islands run clockwise or anticlockwise depending on which way the wind lets you get home.
• Long legs start at dawn. The wind is lightest overnight and peaks in the early afternoon, so the miles get covered before breakfast — even though the overnight drop is smaller than most people expect.
• We aim to be alongside before 14:00. In peak season the berth shortage is what actually ruins a day, and it is worst exactly when the wind is up.
• If the Cyclades in early August are non-negotiable, take a motor yacht that can move between weather windows rather than a sailing catamaran on a fixed island-hopping plan.

Forecasting supports all of this. The North Atlantic precursor is identifiable up to four days before an outbreak. Greek operators watch the POSEIDON system run by the Hellenic Centre for Marine Research, which produces a dedicated Cyclades sailing forecast out to five days, alongside ECMWF medium-range guidance.

Is the meltemi changing?

Honestly, the evidence points both ways and we are not going to pretend otherwise.

Studies based on observations and reanalysis consistently find a modest decline. Tyrlis and colleagues found outbreak frequency falling 2.47% per decade over the summer season across 1958–2002. Poupkou and colleagues found Etesian days falling 1.48 days per decade across 1979–2009, not statistically significant, though maximum wind speed fell significantly. A 2025 study in npj Climate and Atmospheric Science covering 1980–2024 found occurrences declining at roughly two events per decade.

Regional climate model projections for the late century point the other way, toward strengthening Etesians as the south Asian thermal low deepens.

The two are not reconciled. Anyone telling you confidently that the meltemi is getting weaker, or stronger, is ahead of the evidence.

Frequently asked questions

More on where and when to charter in our Mediterranean yacht charter guide, and on the Greek islands specifically in our Greece yacht charter guide.