There was nothing in the forecast at the start of the 1979 Fastnet Race to indicate a storm, but a storm came with devastating effect. How and why did it cause such a catastrophic disaster? Neither the track it followed nor the central pressure of the depression was in itself remarkable. Its speed of close to 45 knots was quick, but not exceptional. It was only when it began to slow down and deepen in the 24 hours between midday Sunday 12 August and Monday 13 that it appeared to develop storm tendencies, deepening eventually to 978mb, a central pressure that would be considered deep in winter and this was the height of summer. By mid-afternoon on Monday, satellite pictures showed that the depression was more significant than had been thought and was deepening rapidly to a storm. It has been suggested that it was the afternoon satellite picture that prompted the imminent gale warning that unfortunately was broadcast after the shipping forecast. As the shipping forecast was the primary weather information for most yachts in those days, any warnings out side the scheduled time was unlikely to be heard at sea. Some synoptic charts at the time indicated a trough following behind the cold front. Whether this was the front or a trough behind it, what is important is that there was a large change in wind direction in the region of 90°. This is a significant feature of the storm, with the strongest wind arriving as the pressure rapidly rose after the trough. Gusts contained within the leading edge of squalls can be half as much again (or more) as the average wind speed, making the reported gusts of 80 knots realistic. Diagrams of wind fields produced by the Met Office show this 90° change in the wind direction and when we read reports from the boats of the conditions experienced, it is the sea state that is the one overriding factor that generated problems for the boats. Our understanding of waves is not complete. Records from North Sea rigs show that the existence of very high, or rogue waves is much greater than theory would have us believe. In the Fastnet storm the south-westerly wavetrain would still have been large when the north-westerly waves arrived, creating a very short steep sea and, although the inquiry found that, in theory, neither the shallow water nor tidal stream had a significant effect, competitors who were asked reported that they thought it had made a difference. Although estimating wave heights is very difficult from a yacht, claims of 50ft waves are substantiated by the report from a Nimrod pilot on 14 August of wave heights of ‘50-60ft’. It was the sea state the wind generated that caused the biggest problems, just as it did nearly 20 years later during the 1998 Sydney-Hobart race. Article continues below… Advances in forecasting go hand in hand with advances in computing power. It seems amazing new that the first live TV forecast was made … Continue reading Fastnet Race 1979: Why was the storm so devastating?
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