Tuesday, 2 February 2010

Climatology of Global Ocean Winds (COGOW) Updated for Sailors Voyage Planning

COGOW is an extremely useful weather tool for cruising sailors planning their passages. It has been around for a number of years, but recently updated with all QuikSCAT satellite data up to and including December 2009.

This means that all data available on global winds and currents over a period of five years is factored in to any segment of the globe you wish to look at.

It is quite simple to use and you can find it by clicking on 'COGOW' on your browser. The homepage pops up as per the screenshot shown.

You then click on your area of interest and a transparent blue window highlights it.

Then by clicking on any position of that map a 'wind rose plot' for any area in the segment of interest to you, pops up and gives you the average wind strengths, direction and percentage of time they blow for any month of the year. This is quite a cool feature as the 'wind rose plot' pops up to the right of the image and then changes as you move your cursor around.

Here's what Lee Bruce of Oceanmet has to say about the updated programme:

When passage planning, one needs all the help one can get to choose the right time to go, and the right winds to depart.

The good news is that the excellent Climatology of Global Ocean Winds (COGOW) website, which is of crucial assistance when planning a passage, has just been updated.

ALL the years of available data have been added to make the results more accurate, and the months have been broken in half, to show better the transition between seasons.

For all sailors planning a passage, the more information you have the better, and here Lee Bruce, of OceanMet (a division of Tactical Weather LLC) tells you why certain sites can so much improve your planning:

Traditional climatology records are based on decades of data, and can be useful as long as we understand the limitations. Because the data are averaged over long periods, we can lose a feel for the variations that may occur. Extreme events are masked, so we don't know how bad it could be in a worst-case scenario.

The problem is compounded over vast ocean areas because-until recently-there has not been a reliable data collection process. Ship reports are sparse and tend to be clustered near traditional trade routes. Extreme events may go under-reported because the crew is busy dealing with the problem at hand, and does not have the opportunity to report conditions.

But for several years now, a product has been available that uses sensors on a satellite to measure the wind over open ocean surfaces. The system (reading near real-time data collected by NASA/JPL's SeaWinds Scatterometer aboard the QuikSCAT satellite) scans the oceans twice each day, as the satellite revolves around the earth from pole to pole. Due to the footprint of the sensor, there is a shifting data gap with each pass that is widest near the equator. But overall, the information gathered is very good, and is a tremendous advantage over any previous data-gathering method.

Two of my favorite web sites that use QuickSCAT data can be used to review overall wind regimes for a passage. You can check wind observations on a daily/weekly/monthly basis for a particular year, or averaged over five years for a particular month. Each site has its benefits, and I recommend using both for passage planning.

Oregon State University's site is the one that has just been upgraded. It now shows BI-monthly averages over all the years that these have been collected, and also presents a wind rose to show the wind distribution. Cruising sailors should have this site bookmarked to aid in route planning. The maps are great, but they also need to review the wind roses for the real story.

Extract courtesy Lee Bruce

Here is the URL of the site: http://numbat.coas.oregonstate.edu/cogow/index.html

You can read much more about plotting and reading wind and weather patterns in my ebook 'Voyage of the Little Ship 'Tere Moana' downloadable from my website http://www.sailboat2adventure.com

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