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America's Cup: Predictwind - Fresh breezes again for Day 3


'The America’s Cup Race Course, framed by the Golden Gate Bridge'    Richard Gladwell ©    Click Here to view large photo

Predictwind indicates that stronger winds will prevail for Tuesday, the fifth and sixth races for the 2013 America's Cup. The first race starts at 1.15pm on Tuesday, local time with the second race scheduled for 1415hrs. The 18fters have changed their schedule to non-America's Cup racedays and will not race today.

With the racing at its regular start time of 1315hrs the two feeds produced by Predictwind indicate that winds will be averaging around 18 kts, with the breeze having been up all night at around 10-15kts. The key point is that on the graph image the two weather feeds produced by Predictwind are very close together at race time, suggesting the the certainty of the prognosis is high. Before that there is a little disagreement as to rate of increase of the breeze strength. Although there was fog on the course yesterday and Sunday - the cold air on the sea gets angrily sucked in by the hotter inland systems, increasing the strength of the breeze. Unfortunately the fog is not easy to predict or measure and so it is a random factor in the forecast. Winds do increase to be close to the limit of 23kts just over an hour after the conclusion of racing - any earlier and the limit might be exceeded.


The above image shows the wind speed and direction at 1300hrs with breezes expected to be 18kts 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 close agreement between the two feeds as to the rate of build of the breeze, and 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 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 of 23kts.

The key feature of the forecast is agreement between the two feeds as to the rate of build of the breeze, and again 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 wind will be slightly lighter.

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



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 strength of the ebbing tide and standing waves can be seen in this buoy just to seaward of the Golden Gate Bridge.  Richard Gladwell_©   Click Here to view large photo

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 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 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. 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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3:00 PM Tue 10 Sep 2013GMT


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2013 America's Cup

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