WEATHER The Round the Island Race in 2019 was a classic change of systems race, with one wind for the start, a changeover period then a new wind for the finish – in other words ripe for a long period of light winds to tempt you to retire. When you have two separate systems driving your weather it’s even more important to not just read the numbers off the forecast but to try and understand how the weather is coming in and what physical signs you’ll see. Later on: The forecast chart To start off with: • Low pressure driven, light • High pressure driven, to modrate SW/W/WNW (Figure 1) shows moderate E/ESE • Sunny, 24-26°C the big picture, with the morning and early afternoon dominated by the generally E flow off the departing high moving into the Figure 1: Met Office forecast chart for 1300BST, July 29th North Sea, and the 2019. Contains public sector information licensed under the Open Government Licence v1.0 later SSW breeze driven by the next low coming in from the Atlantic. The tricky bit is what happens in between these two systems.
Figure 2: 0.08° Theyr forecast for 1800 BST on Race Day, issued at 1800 UTC the previous day.
Theyr provided a high resolution forecast for the event (Figure 2), and the model run issued the day before illustrated the change in wind regime well. The changeover from the dying SE into the gradually building SW coming up the Channel is clearly shown.
The wind station at Chichester Bar (Figure 3) shows that the forecast was pretty good – the ESE breeze died off at 1900 BST, was light and variable for an hour or so, then gradually built back in from the S veering W.
Figure 3: wind at Chichester Bar - the new breeze started to come in around 1900 BST Data provided by the Solentmet Support Group
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WEATHER
CONTRIBUTED BY SIMON ROWELL, ROWELL YACHTING SERVICES
