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Old 28-04-2006, 08:49   #1
sjs
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Please, No Politics, But Re: Pilot Charts

I do not want to start any diatribes on global warming, or anything else, but has anyone read any objective scientific information regarding the reliability factor of pilot charts in view of the unprecedented hurricane activity of the last few years?

Their information concerning weather is historical and, therefore, might include this recent activity, but it is based on averages and there might not be enough data to give proper weight to recent anomolies.

In other words, is there any reliable information to the effect that pilot charts are less reliable; and if so, to any objectively measurable degree?
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Old 28-04-2006, 09:49   #2
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You pose a very interesting question. I really doubt there is a 'set in concrete' answer.

My own take on this is to continue to use the charts as the trends they show will probably still hold in regard to seasonal weather for your area of interest.

These charts are averages compiled over long periods of time. I believe in the last 100+ years in which weather data has been compiled the earth has gone through cycles of severe storm periods.

The law of averages http://en.wikipedia.org/wiki/Law_of_averages

However, I think it more important than ever to gather as much knowledge about weather, how to get weather info before and during a passage is more important now. Not letting your guard down even while at anchor.

I would find it very interesting to hear how the voyagers here are getting weather info
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Old 28-04-2006, 10:56   #3
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Weather info.

I go outside.
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Old 28-04-2006, 13:17   #4
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Yeah good stuff Mike. I have a special weather rock. You know the one, if it's dry, it's not raining, if it's wet, it is raining and so on.

In a seriouse look at this though, Do pilot charts give a "Season prediction" based on the two global cycles of El Neno and La Nena. Theses two cyclic factors are the greatest influence in our global weather pattern. Understanding which cycle we are in, gives us plenty of warning as to what weather pattern we will have for a coming season.
Take a look http:/ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/eln/atms.rxml
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Old 28-04-2006, 13:53   #5
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Wheels

Thanks for the link. Looks like a college course in meteorology.

El Nino & La Nina have been going on for as long as recorded weather, won't the pilot charts still reflect helpful info as to time and route of passages?

Some years may require a larger fudge factor

John
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Old 28-04-2006, 16:40   #6
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Yup, I agree that the wet or dry rock method is good, and I appreciated the laugh. I'm guessing I won't get an informed answer on this, as there probably is not an informed answer out there. Jemsea, I appreciate your comments. As it has always been, there are no guarantees with the sea and however prepared the vessel and crew there are risks to be taken. Still, I have to believe the original source of the charts is contemplating this issue, I just have not read anything about it.
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Old 28-04-2006, 18:10   #7
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Weather forcasts

Many sailors check the weather forcasts before leaving and while at sea.
Hurricanes, cyclones, typhoons etc are usually detected before they form, their paths are predicted with some degree of reliability, and this information can be factored into cruising plans.
This becomes very important during the cyclone season.
My opinion is that it would be important for a cruiser to have the ability to move immediatly a cyclone is predicted. (ie. plans for particular ports, compliance with paperwork etc.) may have to be abandoned to head for safety.
If you are not in a safe place then inaction is not an option!
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Old 28-04-2006, 19:18   #8
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Here's a world map of water temp's that could be of some help in predictions. Weather is determined by ocean water temps and this may be of assistance if one were to monitor it daily and compare it to weather of the region of interest as well as being an education tool or even curiosity.

http://www.wunderground.com/MAR/

Here's another that keeps one wondering.

http://www.ssec.wisc.edu/data/geo/west/

And here's one for wave action for different regions.

Enjoy.................................._/)
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Old 28-04-2006, 19:29   #9
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You're implying that the recent hurricane seasons are unprecedented. But if you pay attention to the reports you will hear things like 'first time 2 cat 5 hurricanes hit the US since 1927' or words to that effect. All the hysteria is focused on 2 cat 5 hurricanes but the 'since 1927' is totally ignored. As it turned out, we did not get hit by 2 cat 5 hurricanes in 2005 but we did back in the 1920's. (Not sure exactly the decade). The cycles of hurricane seasons is well documented but ignored by the hysterical media circus.
A lot is made of the rising temps in the N Atlantic but the S Atlantic is cooling, which is typical of the cycles of the hurricanes over an estimated 40 year period. Globally, hurricane activity is running about the same as ever.
Current predictions are that the NE coast will get hit by a big one soon...just like past records show. But it's unlikely we'll get the historic perspective, just more media hysteria.
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Old 29-04-2006, 05:00   #10
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Weather Patterns vs Climate Change

The importance of the Pilot Chart is not in it’s representation of specific values for wind, currents, wave heights, visibility, surface pressure, & sea surface temperature; but in illustrating the general relative weather patterns, by month for those features.

Although specific global climactic conditions may be changing (slowly), general weather patterns remain fairly constant. Hence, we’ll still plan an eastbound Atlantic crossing to Europe for the late spring months (June/July departure), and a westbound crossing to the Caribbean for the late fall months (November/December departure).

Caribbean Hurricane seasons may become extended, and storms more violent & numerous, but they will still occur in the hottest (water temperature) months - which will remain August, September, & October (Caribbean). The Pilot Charts will continue to reflect these patterns, even though the specific quantitative values may be (or not) be changing (more rapidly than normal).

I think the U.S. NIMA “Atlas of Pilot Charts”* and British Admiralty “Ocean Passages for the World” et al will continue to provide and accurate reliable information for their intended purposes, regardless of escalated climate change.

* http://www.nga.mil/portal/site/marit...c24fd73927a759

FWIW,
Gord May
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Old 29-04-2006, 05:36   #11
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I think Gord's said it exactly right. A friend was recommending Virtual Passage Planner to me the other day because it uses mean current and wind data of this type and shapes a recommended routing 'automatically'. Non-labor intensive and entertaining...but over-using historical data IMO. Better to look at where things stand before leaving, monitor them enroute, and adjust to the extent you can. Small boats can not outrace storms but we can try to put the odds more in our favor.

Re: variability, Xort also puts his finger dead-center. We in N America have been on the downside of a storm cycle for 4 decades, a moment in time relative to such global systems, yet relative to our lifespans we consider the last half-century to be a massive time span and so 'representative'. One of the TV weather f'casters showed me data on the storm history of our local Tampa Bay, Florida area by decade, reaching back to 1880. The measure used was 'Cat I or more storm center passing within 100 km of the center of Tampa Bay.' There were 1, 2 or 3 storms that passed inside that envelope each decade from 1880 thru 1950. Since 1950 there have been zero. Most of the shoreside construction in that area has been done SINCE 1950, some of it on reclaimed, low-lying land. We are now on the upswing side of the storm cycle and any realist can see what's coming. When it arrives, hopefully not on a Wilma scale, there will be much made about it...but probably not from the balanced perspective that the storm was both a 'normal' event as well as overdue, and that the land development was 'short sighted' and overly vulnerable.

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Old 30-04-2006, 12:59   #12
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The problem with rules of thumb and averages is that at one level they are what they are but to attempt to then out guess the average isn't a fruitful game. As a pure strategy to look at averages and pick them apart defeats the purpose they serve.

You can do quantitative estimates that would attempt to predict weather for say the next week in a given location OR you can say this chart is an average of 100 years. Which way should we go? The trouble with both approaches is they don't mix together at all without picking the average apart.

To second guess all the averages and try to say well this year is not average and this is different than normal is a poor attempt at a quantitative estimate. You fool yourself into thinking weather is average but not right now. You can be an aaveraged based thinker and know with certainty when hurricane seqason is but you can't be averaged based to say there will be a hurricane at a specific location on July 23rd.

You are sitting in a location deciding to go some place "better". On average you might decide to go north or south for a month long voyage but to get to the next port is more about right now than the average for right now.

Here is a good one. 85% of the time the weather for tommorrow will be like today. This one really is a pretty true statement for most every where. What is it worth to you to know that today? How might you use such an average? Could you really use it?
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Old 01-05-2006, 03:18   #13
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Weather is the state of the atmosphere* at a given time and place (here & now). Weather changes hourly , daily, and weekly.
* air temperature, pressure, humidity, clouds, precipitation, visibility, & wind.

Climate is the average weather in a location over a long period of time. Climate changes seasonally, yearly, or over centuries & epochs. You will see more sun in summer, more storms in fall, more snow in winter, etc..

Paul asks ( rhetorically ?):
”... 85% of the time the weather for tomorrow will be like today...How might you use such an average?...”

I can think of three weather forecasting principles that use averages such as this:

Persistence - Today’s conditions (elements) reflect tomorrow’s conditions. In the tropics, especially at island stations, where day after day the weather is basically the same because the station is affected by the same air mass with no passages of fronts, a persistence forecast that tomorrow is going to be the same as today, is usually quite accurate. The longer a feature stays in one place, the greater its impact will be on surrounding regions, and the more persistence is likely.

Steady-state or Trend - Today’s changes reflect tomorrow’s changes. Thus, if a cold front is approaching the station at 20 miles per hour, then it will continue to move at 20 miles per hour in the same direction; so the forecaster can determine the weather conditions, based on the location of the front, determined by extrapolating its position, and assuming its rate of movement doesn't change.

Analogue - This technique utilizes the fact that existing weather patterns on weather charts, which resemble previous weather patterns on previous weather charts, should produce the same type of weather elements, or phenomena, that the previous patterns produced. These previous patterns can then be used as a guide for making forecasts of weather elements.

HTH,
Gord

PS: Sorry for the condensed & incomplete answer - I have a “bear” of a work-week ahead of me.
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Old 01-05-2006, 04:58   #14
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If I'm understanding Paul's main point correctly - that one can't easily/practically integrate the use of historical and real-time synoptic data - then I have to say my experience is the opposite. These days on most cruising boats this done with every major passage. You ID the typical prevailing conditions, seasonal timing issues, threats (e.g. with an Atlantic Crossing, getting too close to the Azores High or too close to the regular sweeping frontal systems to the N), and build a general strategy around what is essentially a historical picture.

When making the many incremental decisions that produce a passage, you become more tactical and rely on the real-time synoptic data (from Sat, HF pactor, WxFax, RTTY, Net voice f'casts and more) and constantly revisit your routing decisions based on what you're seeing. Is the high shifting N? Then I'll adjust my routing a bit more N'ly, accordingly. Is the LP cell exiting N America both strong and further S than normal? Then I'll put less N in my course or perhaps go S of E. This goes on all over the world these days aboard cruising boats as opposed to the old 'historical-only' approach which was relying on pilot charts and the advice in guide books, which can only offer summary data. However, one always keeps the historical pattern in mind as its a way to keep options open and provide 'tests' against which one can measure how persistent or potentially momentary a tactical picture might be.

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Old 01-05-2006, 13:22   #15
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Here, I would have to say we have an 85% chance the weather will be different tomorrow.
In Auckland , there is a 98% chance the weather will be different in an hr and every hr.
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