windy windy windy

[Norman]

Understanding the weather ......

want to know where the winds coming from .....
Take a look at the coming week (this is posted 5 Feb 2011 so comments are only valid for a few days as the system will then move on .....

Close isobars are windy, wide ones are calm, lows alway go anticlockwise and highs always clockwise.

Notice there is a static high in mid atlantic about level with canary islands, this is keeping the repeated lows being passed from North America pushed north. we therefore get hit repeatedly and wiped out by the consistent westerly winds caused by them as they spin anticlockwise. Notice how deep the lows are (by the number of isobars (lines) requird to show the pressure) thus the high winds.

fingers crossed we start getting some high pressures soon .....

North Atlantic Pressure Chart=

norm

[Kev1n]

A nice concise summary Norman and valuable to anyone who fishes the sea.

As you say, tightly packed isobars mean a steep pressure gradient causing strong winds. The winds go more or less parallel to the isobars, with the wind heading slightly in across the isobars towards the centre of a low pressure or outwards from a high pressure.
High pressures are usually harder to predict and give rise to calmer, settled weather, warm and sunny in summer, cold and sometimes murky in winter. Watching the barometer can show if the weather is going to stay settled if the pressure remains high, or become changeable and windy if the pressure drops. You can also watch for a change in the wind direction to give an indication of whether a low pressure is approaching, bringing worse conditions, or moving away leaving more settle conditions.

Another detail to be aware of is that the low pressures usually have a warm front followed by a cold front. These fronts are shown as the blue or red lines on the weather charts and as they pass they drop rain and cause an increase in the wind speed with a change in direction. You can see the effect of a frontal system as first the cloud increases and lowers giving warning of an increase in wind speed.

High and low pressure systems move from west to east meaning that our weather usually crosses the Atlantic, then the UK before getting to the east coast. Having some idea of what is happening in the west gives an indication of what’s to come for us.

Is anyone interested in a brief summary of waves next?

[The Jester]

Yeah go for it Kev

[Kev1n]

OK. Concentrating on the waves that we get round here, which are formed by the wind instead of water flowing over obstructions.

Waves form when the surface of the water is stirred up by the wind. The more energy the wind transfers to the water, the bigger the waves are. So, if the wind blows over the sea for a long distance it can transfer a lot of energy; this distance the waves are formed over is called the “fetch.” Eventually the waves will grow to a maximum size dictated by the wind strength, the stronger the wind and longer the fetch, the greater the wave size. A north easterly gale travels a long way and with high wind speeds there’s a lot of energy transferred into waves resulting in a rough sea. When the wind is offshore (blowing off the shore out to sea) waves are blown out to sea, starting as mere ripples at the beach and getting progressively bigger further out.

Windblown waves travel in direction of the wind. Winds are described by the direction they are coming from; tidal currents however, are named after the direction they are going. A northerly current will be going in the opposite direction to a northerly wind, this will increase the difference in speed between the air and water so will form bigger waves.

As well as the height of the waves, the other thing to consider is how far apart they are. Small waves close together (short wavelength) can give a choppy sea that throw a small boat all over, whilst a swell of bigger waves gently rising and falling over a longer time will be less noticeable. If the wind or current changes direction and opposes the waves’ direction the wavelength shortens into sharper steeper unpredictable waves; not good to be out in those conditions even if the waves look small.

Finally, waves form and travel slowly and will continue to move even after the wind has stopped. Waves that are the remnants of a storm are usually smooth and rounded with a long wavelength and can be quite comfortable to ride out in a small boat, and excellent for surfing.

For boat fishing off our coast we want westerly winds to flatten the sea leading up to a trip then very gentle winds when we’re out.

[Norman]

Nice one Kev, great explanation ... summed up in the last line excellently westerly prior to a trip.

Ideal conditions would be a high centred mid to southern europe for the 3 days before a trip thus circulating clockwise and pulling warm air from the med which sweeps across the UK in a westrly direction ... then, by the third day, with the high moving north to be eventually centred over wreck number 29 off the tyne by 6.30am 1 hr after low tide on a saturday morning in June.

utopia

norm

[The Jester]

Intereting Kev , is this sort of thing part of your job

[canman]

So, i'm just wasting me time sticking a wet finger in the air then.

[oldessox]

So, i'm just wasting me time sticking a wet finger in the air then.

It's one thing understanding how it all works , quite another predicting what it's going to do , the finger in the air is nearly as accurate as some of the weather forcasts we see , so don't be too disheartened


It's like being back at school on this thread , only interesting All good stuff

Ray

[Kev1n]

Intereting Kev , is this sort of thing part of your job

Thanks Jester. It's not part of the job; just stuff remembered from my old geography lessons and added to over the years through interest in several outdoor pursuits.


Norman, you're almost right but a few hours too early there cannot be such a thing as an early morning in Utopia

[The Jester]

Thats where the problem is...I used to fall asleep in geography...