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sail-world.com -- Louis Vuitton Cup: Predictwind - It's all in the building breeze again

Louis Vuitton Cup: Predictwind - It's all in the building breeze again    
Fri, 23 Aug 2013


Predictwind indicates that winds will follow a typical San Francisco pattern but should be inside the limit for the start of racing at 1.10pm on Friday for Day 5 of racing in the Finals for the Louis Vuitton Cup between Italian Challenger Luna Rossa, and Emirates Team New Zealand.

With the racing back to it regular start time of 1310hrs the two feeds produced by Predictwind indicate that winds will be averaging 16-18kts, and will be gusting higher.

The key to the day is whether the wind will build at the rate the forecast indicates.

The top image shows the wind speed and direction at 1300hrs with one feed showing winds of 16kts while the other is at 18kts - these are only average speeds and gusts will be higher. There is a little variation in the forecast indicating a higher degree of certainty as to the outcome.

The key feature of the forecast is the breeze kicking in early at around 10kts and staying on a plateau until just before 11.00am, if that plateau is extended for a variety of reasons, then racing will take place in more moderate winds, with the increase coming later in the day. Peak breeze is expected just after 3.00pm at 23kts.

The first image shows the wind prognosis for the scheduled start of the second race, when one feed expected the wind to increase more quickly, while the other is a little more gradual. Peak windstrength later in the afternoon is 23kts - agreed by both Predictwind models.


The second image shows a graphic representation of the wind build - confirming the numbers for the prognosis.


The next two images are showing the same style of information except for an hour later around the time of the second race for the day. Winds are creeping very close to the limit, and bearing in mind that these are only average windspeeds with no accounting for gusts, it is likely that the wind limit will be exceeded on the current wind information.



The fifth chart shows the wind expectations for the following day, Thursday, which shows a reduction in the strength of the breeze, allowing officials some scope to catch-up if required.


Two weather feeds are used by Predictwind, the key to the accuracy of the forecast lies with the graphs, as when the two lines for the two feeds are quite close together and following each other in the trend, then the likelihood of the forecast is high. If there is separation to any marked degree, then there still some issues to be resolved but usually 24 hours from the race they are well aligned.

The Predictwind model takes various weather feeds and then polishes these, part of this process is factoring in the effect of local topography on the breeze - well demonstrated by the image with the funneling of the breeze.

Developed by former Olympian, Jon Bilger (470, 1992), PredictWind?nid=113460 application was used by the Swiss team Alinghi to win the 2003 and 2007 America's Cups, and has become the leading wind system used by racing and recreational sailors around the world. It is available on a subscription basis and also with a free forecast option.

A mobile app for Android and iPhone is available and PredictWind?nid=113460 is probably the most used app on the Sail-World iPhone.

Real time local wind observations have been added as further functionality.

You can check the weather anywhere in the world, and get a five day forecast, plus a variety of other features and functions of PredictWind?nid=113460. The app is synchronised with your PC, so that your latest set of locations are always available without resetting each time you change a device.

by Richard Gladwell



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