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Peaceful Christmas in the With a vigorous westerly flow well north of the fleet, skippers in the Vendee Globe enjoy a rare treat as they cross the half-way point of the race. December 27, 2000 Race leaders Michael Desjoyeax (PRB) and Roland Jourdain (Sill) crossed into the Pacific Ocean during Christmas day, as they sailed south of Tasmania and celebrated the half-way point of the race. "They have covered 11948 miles, nearly 21500 kilometres, and there remains the same distance to the finish," said race organiser Philippe Jeantot. Six days ago, the two leaders nosed into variable easterly winds south of a depression forming below western Australia. That low, combined with a ridge of high pressure to its west, helped to kink the jet stream above it and in turn alter conditions in the southern ocean. The normal west to east flow at about 48 degrees south ground to a halt for a couple days, as the kink created a blocking pattern. The ridge of high pressure from the Indian Ocean worked well south towards Antarctica and the low south of Western Australia stalled. Helping this slow-down was another kink in the jet stream east of Fiji, which kept a high pressure cell parked east of Australia - which in turn checked the west to east flow of weather across the southern Tasman Sea. Sounds Complicated? It is. And the Pacific is full of this kind of stuff. The race may be half-way over, but the challenges are almost just beginning ... Anyway ... nothing last forever in the deep south and it wasn't long before things got under way. And when that low south of Australia did move, it dragged a vigorous westerly air stream with it - created in large part by a deep low driving to the east in the days before Christmas. Southern Ocean south of Australia
and New Zealand The band of tight isobars extending from south-west to north-east below Australia indicate a vigorous westerly flow - the kind skippers might expect further south at this time of year. Note how the high east of Australia is helping to push the westerly flow south of New Zealand. A monsoonal trough over Central Australia would have allowed the jet stream above and the westerly flow further at the surface to travel further north. Pressure chart courtesy of Australian Bureau of Meteorology December 24, 0300gmt Fleet leaders avoid the heavy westerly winds to their north and skirt the epicentres of a band of low pressure to their south - resulting in calm Southern Ocean conditions: About 20 knots of wind from their starboard quarter. Picture courtesy of Virtual Spectator.
White Christmas in Tasmania Race leaders skipped along comfortably in 20 knots, just skirting the epicentre of a band of low pressure well south of Tasmania (See image above). But conditions to their north told a different story: Hobart's Mt Wellington recorded a daytime high of 4 degrees C with snow flurries the day before Christmas, as that low passed to the south of the island, dragging cold Antarctic air up to latitude 43 degrees south. Winds at Maatsuyker Island preceding that low blasted in from the north-west at 133kph, or 66knots.That's a heckuvalotov wind, but there are some things to remember here: Maatsuyker Island, about 15 miles south east of Tasmania's South-West Cape is about 900 feet high and the lighthouse which records wind strength stands about two-thirds of that height. Wind strength up there is going to be a lot stronger than at the surface. And another thing - we're not sure if that was sustained, or a top gust, but whatever the case, the Australian Bureau of Meteorology had predicted storm force winds from the north west for December 23. Meanwhile, 2000km to the north people celebrating Christmas eve at Casino on the north coast of NSW sweltered in 40 degrees of heat, after days of northerly winds pushed south by that blocked high east of the Australian coast. That blocked high effectively stalled a low pressure trough stretching between the deep low south of Tasmania and monsoonal activity over the Northern Territory. Is this getting away from our story at hand? Not really ... For race leaders in the Vendee Globe, that blocked high helped to push the low south of Tasmania even further into the southern Ocean, preventing these skippers from facing a barrage of easterly winds, and presenting them with a relatively quiet Christmas at sea. What lies ahead? We're not game to take a bet, but looking at the upper level charts for Australia, it appears another blocking system - very similar to last week - is taking shape. We expect more of the same for a few days yet, but as skippers sail below New Zealand and into the Southern Pacific Ocean there are a few things to consider: More funny weather, with low pressure cells positioned north and south of blocking features. Cyclogenesis in areas of permanent cloud band (One in particular stretches from the Coral Sea east to Fiji and then tends to curve south east into the Southern Ocean) More ice. This in particular is a concern for race organisers, who have created a waypoint at 57 degrees South north of the Ross Sea. This area of Antarctica creates the most ice, due to a number of glaciers spilling off the Antarctic plateau. In fact, we know that sea ice is much more prolific this year, perhaps due to a calmer-than-usual winter in the deep south. Commander Steve Wheeler of the US Coast Guard icebreaker Polar Sea told us that there is a LOT of ice banded from about 145E, out further than the Balleny Islands, and extending clear across the opening to the Ross Sea. Whether that sea ice has had time to scatter with early summer storms, and whether it will affect the Vendee Globe fleet is not known. © weather-wise.com 2000 Upper level winds over Australia
and
Look at that funny kink in the jet stream over central Australia and, particularly, south of western Australia. Expect a ridge of high pressure from the Indian Ocean to dive well south, while a cold blast from the Antarctic will chill Tasmania, and the front-runners in the Sydney to Hobart. Pressure chart courtesy of Australian
Bureau of Meteorology
December 26, 1300gmt
Fleet leaders negotiate a large mass of low pressure, hoping to get into winds flowing from the north-west along its leading front. Look at the ridge of high pressure behind them - the result of that kink in the jet stream (see above). Looks like this system will stall for at least a day, until upper level wind flow straightens itself out. Picture courtesy of Virtual Spectator.
How the skippers saw Christmas Michael Desjoyeaux: "Night is just about to fall as we bend round the little depression and I hope to have more wind afterwards. Calmer conditions can be good just to get out of your oilskins for a bit. I haven't got all the sails up though, as the weather is still variable." Ellen MaCArthur: "The wind is changing a lot, but stays at around 20 knots, and I'm going at around 13 - 15 knots, under gennaker with 1 reef in the main sail because a squall is about to pass through. I'm more reaching than downwind." Josh Hall: "The weather is better, 30 knots from the WSW, and we¹re reaching better boat speeds. For 4 days I was trapped in an anticyclone with not much wind." Philippe Jeantot on magnetic disturbance "The geographical South Pole is of course, not superimposed on the magnetic pole, and the latter is much nearer to the skippers¹ route. What happens is that the rose on the compass continuously rotates 80 degrees either way quite gently, which in turn feeds incorrect information to the autopilot, and it becomes impossible to steer the boat without throwing her off course up and downwind. This was the lot of Thomas Coville (Sodebo) and Marc Thiercelin (Active Wear)." says race organiser Philippe Jeantot. And, on ice risk: In the first Vendée Globe there was no Southern latitude boundary in the rules and pushed on by a racing demon, we were all cutting corners and descended very low indeed. It became a real Russian roulette as we slalomed in between the icebergs in dense fog. For each edition of this race, the Southern limits have been raised further North. This year the skippers have several way points at 57 degrees South, which they must leave to starboard. In between these fictitious markers they can choose to descend lower and follow a more direct, shorter route, but they must climb North to round the next way point. These marks are in place to ensure that the boats avoid the most dense patches of ice flow (off the Ross Sea). Explore comment from From the project manager, Mark Turner , December 25 ... |