THE Fastnet storm of 17 years ago has a double entry in the Guinness Book of Records. It is remembered as being responsible for the worst yachting disaster in history, but in its wake there occurred a unique optical phenomenon the rainbow with the longest known duration.
Just over 300 yachts started the 28th Fastnet Yacht Race from Cowes on August 11th, 1979. The weather chart that day showed the harbinger of doom very clearly, but it looked innocent a shallow depression of 1004 hectopascals just off the coast of Nova Scotia. During the two days that followed, however, this Nova Scotia low moved eastwards, and in mid Atlantic it intensified explosively and unexpectedly. By mid day on August 13th th«MDBO»e«MDNM» depression had reached a position 300 miles to the west southwest of Ireland winds of hurricane force reached the Fastnet area just before 11 p.m. that evening, and during the next six hours winds of up to 80 m.p.h. lashed the race area, generating waves 40 to 50 feet in height.
Of the 300 starters, only 85 had made it round the Fastnet Rock and back to the finishing line at Plymouth by the time the race officially ended on August 16th in the meantime 23 yachts had been abandoned at sea, five were known to have sunk, and 18 participants in the ill fated event had lost their lives.
But the clouds of the Fastnet storm had, if not a silver, then a multicoloured lining. The depression responsible for the havoc moved across Ireland early on August 14th, and by evening it had reached the east coast of Scotland. During the afternoon it provided a showery northwesterly flow of air over north Wales, and it was there, near Llandudno, that these showers, merging one into the other and yet allowing access to the sunlight, produced a rainbow that lasted for a full three hours without a break.
Of course the full rainbow is rather like a colour television picture. As you look at a distant shower of rain illuminated by the sun behind your back, each drop provides a single spot of colour it is the combination of millions of such water drops, each making its own individual contribution, that provides the whole picture. Indeed one could argue that although the north Wales rainbow of August 14th, 1979 appeared to last for three hours, it was in reality a 3 hour series comprising a myriad of individual rainbows that were continually forming, disappearing, and again reforming, as drop replaced drop in the required position.