Louis Vuitton Cup: Predictwind - Strong winds despite changed start

Luna Rossa Challenge 2013 Louis Vuitton Cup Final - Race 2
Red Moon/ Studio Borlenghi / Borlenghi-Butto

Predictwind indicates that winds will be just under the limit for racing in the third and fourth races of the Finals for the Louis Vuitton Cup between Italian Challenger Luna Rossa, and Emirates Team New Zealand when they meet on Monday August 19, 2013 in San Francisco.

On Sunday, official bought the start time forward by an hour to try and get lighter winds and enable racing within the limit of 18-19kts (depending on the state of the tide). The first 25 minute race is due to start at 1210hrs local time, with the second about an hour later.

The top image shows the wind speed and direction at 1215hrs with one feed showing winds of 15kts while the other is at 18kts - these are only average speeds and gusts will be higher. There is a small amount of variation in the prognosis, with the point of disagreement being in the rate of increase of the breeze, rather than the actual strength. The breeze peaks at about 1500hrs (3.00pm local time) at a speed of around 23kts - well in excess of the wind limit, but interestingly within the limit of 25kts for the America's Cup.

The prediction indicates that the winds should just be within the limit for the first race, but the second race of the day is marginal.

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

Predictwind - Wind Map for 1215hrs on Monday 19 August, 2013. The right hand frame shows the second weather feed expecting slightly lighter winds at this time

Predictwind - Wind Graph for 1215hrs on Monday 19 August, 2013

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.

Predictwind - Wind Map for 1315hrs on Monday 19 August, 2013. The right hand frame shows the second weather feed expecting slightly lighter winds at this time.

Predictwind - Wind Map for 1315hrs on Monday 19 August, 2013

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

Predictwind - Weather predictions for Monday 19 and Tuesday 20, August, 2013 - San Francisco

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), www.predictwind.com!PredictWind 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 www.predictwind.com!PredictWind 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 www.predictwind.com!PredictWind. 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.