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America's Cup- Predictwind - Lighter winds and late build for Day 1

by Richard Gladwell on 6 Sep 2013
The America’s Cup Race Course, framed by the Golden Gate Bridge © Richard Gladwell www.photosport.co.nz

Predictwind indicates that light to moderate winds will prevail for Sunday, the first race day for the 2013 America's Cup. The first race starts at 1.15pm on Saturday, local time with the second race scheduled for 1415hrs. The 18fters racing in the International Series will have stronger breezes when they start racing around 1530hrs.

With the racing at its regular start time of 1315hrs the two feeds produced by Predictwind indicate that winds will be averaging around 10-15kts, however the key point in the forecast is that the breeze builds very sharply and if that increase in strength is delayed then races could be sailed in winds of 10kts.


The top image shows the wind speed and direction at 1300hrs with breezes expected to be only 10-12 kts at the start of Race 1 - these are only average speeds and gusts will be higher, but not enough to exceed the wind limit. 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 disagreement between the two feeds as to the rate of build of the breeze, but around race start they are consistent in their projection.


The second image (above) shows a graphic representation of the wind build - confirming the numbers for the prognosis. If the breeze builds later than predicted, then the light winds soon one the left of the graph will extend through to the race start time.


The top image shows the wind speed and direction at 1400hrs with breezes expected to rise to 15-18kts at the start of Race 2 - these are only average speeds and gusts will be higher, but not enough to exceed the wind limit.

The key feature of the forecast is disagreement between the two feeds as to the rate of build of the breeze, but around race start they are consistent in their projection.


The second image (above) shows a graphic representation of the wind build - confirming the numbers for the prognosis. If the breeze builds later than predicted, then the light winds soon one the left of the graph will extend through to the race start time.

The third chart (below) shows the wind expectations for Saturday and Sunday. Note that sea conditions described in this chart are based on open water and are not descriptive of an enclosed harbour



The image below shows the wind speed and direction at 1500hrs for the 18fters with breezes expected to be peaking around 20kts at around 1600hrs - these are only average speeds and gusts will be higher, but not enough to exceed the wind limit. There is a little variation in the forecast indicating a higher degree of certainty as to the outcome.



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.

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