Meteorology and Weather Routing
Meteorology in the Greek Category A exam is regional, not generic: the meltemi, the bora and Vardaris, the sirocco, summer thunderstorms over the mainland, and the acceleration of wind between islands. You are expected to read a synoptic chart and a gale warning, use ΕΜΥ (HNMS) and Navtex products, and turn a forecast into a routing decision.
Pressure, wind and the barometer
Close isobars mean a strong gradient and strong wind. Buys Ballot's law in the northern hemisphere: with your back to the wind the low centre lies on your left, roughly 90° plus 20–30° forward because of surface friction. A barometer falling 3 hPa in three hours signals a fast-approaching system; in high summer the Aegean pressure is usually steady, so any fall deserves attention.
The Greek wind regime
- Meltemi (Etesians): N to NW in the Aegean from June to September, typically force 5–7, strongest in the afternoon, accelerated in the channels between the Cyclades and off headlands such as Kafireas, raising steep short seas.
- Bora: cold, gusty NE to N katabatic wind; the Vardaris is its northerly form in the Thermaic Gulf.
- Sirocco (Notias): S to SE from Africa - warm, humid, dust-laden, poor visibility.
- Sea breeze: summer onshore wind building by midday to 10–15 kn, dying at night; where it opposes the meltemi it produces confused seas.
Routing decisions
Plan legs so shelter is reachable within a few hours; avoid lee shores with a meltemi blowing off them; remember that headlands produce gusts and that night-time katabatic drainage can be stronger than the forecast.
Worked example
A 6 kn yacht must beat 60 NM north into a force 6 northerly. Close-hauled she sails 45° off the wind, but 10° of leeway means her track is 55° off the wind. Velocity made good along the wind axis = 6 × cos 55° = 3.44 kn, so 60 NM takes about 17.4 hours - three hours more than the tide-free straight-line guess, before allowing for reduced speed in the seaway. Reasoning: leeway is added to the track angle, not the heading, and it costs VMG on every tack.
Traps that cost marks
- Confusing wind "from" with wind "toward" when plotting.
- Forgetting that in the northern hemisphere the wind backs ahead of a warm front and veers after the cold front passes.
- Using an area forecast but ignoring local acceleration between islands and night katabatic gusts.
- Treating a sea breeze as harmless when it opposes a meltemi.
- Ignoring Navtex gale warnings issued after the morning forecast.