RTIR Weather Briefing

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Race meteorologist Chris Tibbs gives the Raymarine Weather Briefing at the J.P. Morgan Asset Management Round the Island Race and here he offers All at Sea readers essential race advice.

In late June around 1600 boats of all shapes and sizes will be out on the Solent for the Round the Island Race. From large classic yachts like Mariquita from a bygone era to the latest high tech wizardry rushing around and arriving home for lunch, they all have one thing in common – the weather.

Whilst it is impossible to give a long range forecast for the race, typically it will be run in light SW wind early in the morning, picking up through the afternoon making it exciting around St Catherine’s before beating back up the Solent against the tide.

However it is not always how the averages tell us it is going to be.

As with all yacht races, your chance of success is largely down to preparation. This includes preparation of the boat and planning your tactics depending on wind and tide.

WEATHER PATTERNS

Chris 2015

Whilst we can work out the tides well in advance, the weather is not so predictable. A week ahead of the race we can start to look at weather patterns. We are looking at how settled the weather is; where highs and lows are expected to be and how much the forecast is changing from day to day, which is an indication of uncertainty.

A week out it is impossible to be too precise, but we should know if it will be sunscreen and salads or oilskins and soup.

As we get closer to start day we can refine the forecasts; there are huge numbers of sites online to do this and I am sure we all have our own favourites. Generally the free wind forecasts like XC weather or Windguru are based on the American GFS model whilst the UK met office site is on their own model so there will be some differences.

Having followed the weather patterns through the week how can we get a better feel for the day?

TIME AND PLACE

As we know the weather can be quite different in areas just a few miles apart and also it does depend on the time of day. Early morning, as the land is cool, the wind is usually light and more variable. As the day warms up some of the energy from the sun is transferred to the atmosphere and the wind picks up. Enough warmth in the day and a sea breeze may develop but this depends on other variables not just the temperature.

We also know that the wind will be strongest around headlands and where it is funnelled by the land, so the places to watch out for are around St Catherine’s and also coming up to the finishing line. But it is around St Catherine’s that it can become dangerous for not only is there the stronger wind, but also the tide.

Wind against tide produces some nasty overfalls and it is a balance between being close to the rocks and the risks inherent in being there, or well offshore to avoid the tide rip. This can prove rather too exciting if already flying a spinnaker in marginal conditions. Weather forecasts, therefore, need to be modified to take account of local conditions where the wind may be accelerated and the wind’s interaction with the tide.

I will be looking at the weather during the build-up to the race, which will be online at raymarine.co.uk, and there will be the usual Live Raymarine weather briefing at the Island Sailing club on 26 June at 18.00. This will also be streamed live on to the Raymarine website.

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