Weather Window

[JCFARER]

Hello all,

The wife and I have been tangling with something that we hear often "weather window" and think we have an idea as to its meaning but would like some "distinctive" clarity.

Monohullers and Multihullers, sail or power, are welcome to respond. We are interested in all that knowledge but intend to purchase a sailing multihull so those responses are very important.

Here goes. What is the ideal "weather window" and what criteria must be met. For example: a planned heading of 180Deg, for 600Nm, at a speed of 7Kn, on a vessel weighing 20K#'s eventually hitting doldrums or entering the trades would mean that the ideal "weather window" is (Fill in the blank)..... and, what drives that criteria. The tide and wind from which direction to the heading, etc...etc...?

I know, many, many variables...but share a "real" occurence if it gives better clarity. Oh yes, explain that the push of a button on a computer gave you all the information...wind, tide, etc...that you needed to warp into action, but please, also explain the process if you didn't have all of these technologies available. If you believe it is only good for a small distance and after that it's a crap-shot until you arrive, then explain that also.

Thanks...we will follow this one closely since we have as many definite logical ideas as we have erratic and oppossing.[^]

Fair winds,

J

[JeanneP]

I think you'll find that weather windows come in all sizes and flavors, depending on location.

Basically, a weather window is a forecast for reasonable weather for (x) number of days, followed by ...... The "followed by" might be good, it might be bad. For example, as we are heading south, a reasonable weather window might be one or two days of calm weather, with a change to colder weather with winds increasing out of the north to 15 to 20 knots. Reasonable window, we bolt south, the further south we get the later the heavy north winds might hit us, but they would still be welcome because they would be pushing us south rather than slowing us down.

When we were in the Gambier and Austral Islands, the southernmost of the islands of French Polynesia, weather fronts would roar through there on a fairly predictable pattern. The winds would ease, switch from easterly to westerly, roar hard for two or three days, the wind would start clocking around back into the east, you'd have a few (3 to 10) days of easterly trade winds, then it would start again. Forecasting consisted of watching the low pressure systems as they moved through, and bolting as soon as they were past. As the winds shifted again you would anticipate the change to bad weather and start reefing early.

Elsewhere in the S. Pacific the Intertropical Convergence Zone (ITCZ) wobbled north and south, affecting the weather. You would track it until it was in a favorable position for you to bolt to the next island group.

This is local knowledge (well, "local" in the sense that each region has its own weather quirks) to some extent.

In the Bahamas, you watch the weather and do not budge when a norther is expected to come through. Or you head for a safer anchorage in anticipation of that norther arriving. Because northers are nasty in the winter in the Bahamas, and in some places downright dangerous.

This is a quick explanation of the idea of a weather window. As I said, each region has its own "flavor" and peculiarities.

[Spike_dawg]

There are so many factors it would take a novel size reply for everything involved. Jeanne sums it up nicely as to what it is.

I think you are also looking for how to do it. As Jeanne replied, it's dependent on the weather patterns and time of year for the area. Also the discrete forcasts for the LENGTH of time you are sailing. That's defined by the boat polars...how fast you sail with different wind speeds and directions. Also how fast you sail for your level of comfort and passengers on board.

There are all kinds of weather factors you look for, or look to avoid, and some of these are also area dependent. A low pressure system to the north of Hawai'i is often a good thing, north of New Zealand a bad thing.

Weather patterns can be found in Cornells World Cruising Routes, sailing atlas's of the Pacific and Atlantic and also various web sites. Here's one for the pacific. http://www.pangolin.co.nz/almanac/analysis.php

Actual weather forcasts are available from multiple sources, again dependent on the area involved. Weather gribs are also available (free) from NOAA or sailmail. Weather fax (free) over ssb or internet.

Professional weather routing is also available for a fee. Some of these people are extremely accurate...others not so good.

I had a list of Bob McDavitts weather to look for to make the journey from Tonga to New Zealand. If I find it again I will post it here. It's a comprehensive list of weather patterns which open a "window" to make a safe sail. I think it's available on line but don't have the link.