Katabatic winds

[neil1967]

I think I understand about Katabatic winds - hot air around the top of steep sided hills cools in the evening and sinks down the valleys causing gusts. Given that, is it actually possible to predict when katabatic winds will occur - clearly you need the mountains/hills, but is there a set of ideal conditions that cause katabatic winds that I can look out for, so I have a better idea of when they might occur?

 

[DownWest]

Stories about Drake's passage and other wanderings near Terra del Fuego suggest that they are not very predicable.

 

[Norman_E]

It depends where you are. I once stayed in a hotel in Turunc near Marmaris and there was a katabatic wind every evening. The combination of a hot sunny September day and the steep mountainside behind the town did the trick every time the sun went down and the clear skies let the heat radiate away..

 

[RichardS]

The Croatian met service are very good at predicting the onset of the bora, which is their strong katabatic wind. However, without access to their weather station data I don't think you would have much success.

Richard

 

[Skysail]

In the Ionian, mountains around Vassiliki generate katabatic winds reliably. From a flat calm at noon, by 6pm it is blowing force 8. Windsurfing is very popular as the conditions suit everyone from beginner to expert, depending on the time of day.
So I guess if the sun is there consistently, you can forecast the wind.

 

[mikegunn]

My first experience of a vicious katabatatic wind was when anchored in Cala Di Mascarat in Spain. Around sunset it was very still. No wind. Eerily so. We’d gone ashore but my partner said she felt uncomfortable and that we should return to the boat, which was anchored in the Cala. Just as we arrived back on board the wind hit. Within seconds the anchor was dragging and by the time I’d switched on instruments and engine we were seeing 50 knots of wind. I’d put out 70 mtor’s of chain and suddenly the anchor bit but the force was sufficient to deform the bow roller. Five minutes late the wind died to a whisper, as though nothing happened. I believed that katabatic winds we’re caused by a lump of cold air which had been prevented from descending by rising warm air, suddenly loosing that support. That fitted in with our location. The Cala has a steep rock face adjacent, topped by a plateau. I have since experienced other instances of katabatic winds, particularly in Greece. They haven’t always been associated with sunset either. It seems that wherever there is a lump of relatively cold air being supported by warm air, should the thermal collapse the cold air can plummet down.
Mike

 

[colind3782]

We got knocked down by a katabatic wind off the Rock of Gibraltar which came out of nowhere straight on the beam. In hindsight I suppose I should have expected it but I didn't.

 

[RupertW]

In the Ionian, mountains around Vassiliki generate katabatic winds reliably. From a flat calm at noon, by 6pm it is blowing force 8. Windsurfing is very popular as the conditions suit everyone from beginner to expert, depending on the time of day.
So I guess if the sun is there consistently, you can forecast the wind.

That’s why I like anchoring there lots of other equally predictable but less extreme places in the Med. Lazy calm breakfast and swim in a nearly empty bay, time to dinghy ashore for shopping and lunch then watch any day anchorers clear out by mid-afternoon regular Force 8 while you siesta, take photos of the windsurfers and kite surfers and once the sun goes down it just dies away for a calm supper with no breeze at all. And repeat.

 

[Joker]

I experienced it when I was anchored in Lulworth Cove for the first time. I could hear the wind in the rigging, and wondered whether it was safe to raise the anchor and leave the Cove. When I got out into the open sea, it was as flat as a millpond.

 

[Metabarca]

In the Adriatic, you will usually have two or three days' warning of the bora, which can be caused by an imbalance in pressure north and south of the Alps, and accelerates as it hits the coast (always strongest in the Quarnero/Kvarner as the mountains are higher there and right up at the coast. If you see clouds low over the mountains, the bora is about to hit.
In Tierra del Fuego (known as williwaws), much less predictable, as there are so many mountains and channels. You can see them churning down the Beagle Channel from high up, but I believe they're especially bad around Cape Froward, where the cape itself is a high mountain. Spending the night at anchor in these waters means tying yourself down with a spider's web of lines in all directions.

 

[Zarro]

Not sure if it is a true katabatibc wind, but if you have been in Cascais for some time you will know that we often get strong winds all night, which pick up about 18.00.

 

[neil1967]

Not sure if it is a true katabatibc wind, but if you have been in Cascais for some time you will know that we often get strong winds all night, which pick up about 18.00.

Yes - been here for a couple of years and have had the yacht here for just over one. Looking to get round to Sesimbra where I understand they frequently get katabatic winds, but it would be good to try and understand if there were times I could avoid them!

 

[Uricanejack]

To put it real simple.
similar to the conditions for land and sea breezes.
only a bigger or more pronounced effect.
high pressure system over the area. In particular over the interior( UK doesn’t have an interior) Still can get a katabatibc wind.
Usually not as strong as.
large continents do.
so a katabatic wind from the interior of continents may not be diurnal and can last for days. if there is a persistent high pressure inland.
So higher pressure over continent and relatively lower pressure over sea.
where they occur regularly they get local names.
often worse in winter. They can exceed 60 or 70 knots here.
even in summer, just passing a point at the entrance to inlet can see a wind increase couple of numbers on the Beaufort scale. The water will show it.

 

[Laser310]

true katabatic winds are gravity-driven down-slope winds - so at a minimum, you need some topography.

they occur in the Caribbean near some of the taller islands, but are usually pretty weak. locals often often referred to them as drainage winds.

drainage winds can be important in the Caribbean 600 race, particularly in the wind shadow behind Guadeloupe.

 

[Yngmar]

Looking to get round to Sesimbra where I understand they frequently get katabatic winds, but it would be good to try and understand if there were times I could avoid them!

We've spent a worryful night at Sesimbra, anchored near a pier off the beach outside the marina. Our Rocna held in the sand, but it wasn't exactly restful with 50+ knot gusts howling down the mountain. Impressive demonstration of katabatic winds though. Never had it quite as much anywhere else, but then we learnt to heed the warnings more carefully

 

[HissyFit]

Stories about Drake's passage and other wanderings near Terra del Fuego suggest that they are not very predicable.

Drake would have had nothing better than an hourglass to tell time, and a judgement of local noon by observation to set it by, so to say that katabatic winds are not predictable going by his experiences is to dismiss 400-odd years of timekeeping development and navigational experience too lightly. Drake wouldn't have had the knowledge of the terrain inland, which drives the off-shore winds. If he knew then what is known now, he'd probably have a good handle on what issues the landmass can cause , weather wise.

By what other posters have written, a fit seems that a familiarity with an area is needed to learn local conditions.

 

[DownWest]

Drake would have had nothing better than an hourglass to tell time, and a judgement of local noon by observation to set it by, so to say that katabatic winds are not predictable going by his experiences is to dismiss 400-odd years of timekeeping development and navigational experience too lightly. Drake wouldn't have had the knowledge of the terrain inland, which drives the off-shore winds. If he knew then what is known now, he'd probably have a good handle on what issues the landmass can cause , weather wise.

By what other posters have written, a fit seems that a familiarity with an area is needed to learn local conditions.

I wasn't refering to Drake himself, but the area. A recent foray there in a small boat had to be aborted because of the unpredictable winds

 

[Stemar]

they're especially bad around Cape Froward

Well named then.

Froward: (of a person) difficult to deal with; contrary.

A word I'll be saving to describe a few people in the Lounge

 

[dulls]

I think I understand about Katabatic winds - hot air around the top of steep sided hills cools in the evening and sinks down the valleys causing gusts. Given that, is it actually possible to predict when katabatic winds will occur - clearly you need the mountains/hills, but is there a set of ideal conditions that cause katabatic winds that I can look out for, so I have a better idea of when they might occur?

I was moored in Nelson New Zealand once. You could set your clocks to the Katabatic winds. We were there in the summer and they blowed everyday then. To avoid them as much as possible anchor on the points and not the centre of the bay.