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Old 17-01-2013, 22:41   #1
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The next learning curve: Meteorology?

After reading this tonight, "A very dangerous 936 mb storm peaked today over the western North Pacific with a min pressure of 932 mb and is moving northeast at 25 knots with hurricane force winds and very high sea and swell conditions. Hurricane Sandy, by comparison, reached a minimum pressure of 940 millibars and was the largest Atlantic hurricane in recorded history."

I realized how little I know about the weather and understanding the forecast. I studied the governnment text, "The Wind Blows Always" which taught a little about prevailing weather pressure-slopes but I didn't get much out of it.

My Barometer only tells me one thing, pressure is rising or falling giving me a clue as to what is coming. I don't pay much attention to what the millibars are.

So 932 mb is an extreme low found only in a huge hurricane?
How high can the pressure go?

What equipment do you rely on for weather forecasts while passage making?

How easy is it to see an approaching storm and avoid it when at sea?

What books best prepare a sailor?


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Old 17-01-2013, 23:45   #2
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Re: The next learning curve: Meteorology?

The thing about Sandy was not the intensity (ie the depth of the depression) but the size of the system. That's why the winds were not particularly strong: if you think of the isobars as contours on a map of hilly terrain, the closer together they are, the steeper the 'gradient'. And windstrength is generally a function of the steepness of that pressure gradient.

The 932hPa (same as millibar) pressure for the current system is quite low in comparison with standard pressure of 1000hPa, and you can expect strong winds, but there was a typhoon in that part of the Pacific called Megi (unofficially a super-Typhoon), in 2010, which got down to 885hPa, and had sustained winds (ie for periods of at least 10 minutes) of 230 kph

One rather scary thing about the current storm is that it's almost the least likely time of year, when you'd expect sea surface temperatures to be at their lowest. (which is what tropical revolving storms feed on for energy)

In this part of the Pacific, typhoons can happen at any time of year, but most of them happen (depending on how you define 'most') between about June and October.

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Old 18-01-2013, 00:06   #3
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Re: The next learning curve: Meteorology?

I'd suggest starting with your local weather.

Hunt round and find your local weather forecasts on the internet, in particular marine weather.

Look for wind speed, wave height, wave period, swell, rain, fog and so on.

Get used to relating the weather forecast to what you actually see.

The other aspect to interpreting weather forecasts is to work out how they relate to condition that you want to sail in.

I learnt my basic weather when I did my private pilots' license (read book, answer questions) but there must be many good books on the subject.
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Old 18-01-2013, 06:57   #4
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Re: The next learning curve: Meteorology?

Originally Posted by eliems View Post

What books best prepare a sailor?

Here are two, often recommended, ends of the spectrum:

Reeds Maritime Meteorology (Reeds Professional): Elaine Ives, Maurice Cornish: 9781408112069: Books


Instant Weather Forecasting: Alan Watts: 9781574091366: Books
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Old 18-01-2013, 08:15   #5
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Re: The next learning curve: Meteorology?

Yes anything written by Alan Watts. I once taught a course in weather although I'm far from an expert. This is an immense topic and one cannot predict much from a single station (your boat),however listen to noaa, and simultaneously looking at weather maps in your newspaper and the satellite animations that are shown on TV.Do all this while looking out your window and studying the sky while on board and you will in time learn something. Make the foregoing an ongoing process throughout each day because you want to be able to spot the trends and correlate them to what has occurred earlier.
So the barometric pressure means little in itself,but is it trending up or down ? Most of the readers here are in the mid latitudes which is predominately a story of air masses and their movements and interactions. Some lucky few are in the tropics where the weather is more predictable with different inputs ( e.g. tropical waves).
Some nut cases here, long for high latitudes with their never ending low pressure systems and attendant cloudy days. But surely the place to start is your own backyard no matter the latitude and you can progress from there. Study the weather as outlined above and you will have added another level of interest to our rich cruising life.
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Old 18-01-2013, 08:44   #6
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Re: The next learning curve: Meteorology?

When I moved from the east coast to the left coast I realized that everything I "knew" about the weather had to be relearned. Things like offshore flows, cutoff highs and the patterns of lows were entirely new phenomena.

You can learn to read the weather charts for your area by reading them every day. You'll begin to recognize patterns of how fronts come and go. Every once in a while something will surprise you. This is normal.

This latest storm even has the experts shaking their heads. Where did all this energy come from in January?

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