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Record pace as east Atlantic high develops north of leading yachts What variable winds? Vendee Globe 2000 leaders simply surf their way towards the ITCZ November 19, 2000 It has been a matter of being in the right place at the right time, for skippers in this year's Vendee Globe 2000. From Cape Finisterre, when yachts caught north west winds circulating around that deep British low, to the Canaries when a moderately strong high (1024hPa) developed to their east, these sailors have had a downwind ride all the way. Now, as yachts approach the Cape Verde Islands (leader Yves Parlier is expected there today), that high which developed east of the Canaries has deepened to 1028 hPa as a powerful trough to the west squeezes winds between the two systems. At the same time, the Inter-Tropical Convergence Zone (ITZC) has traveled slightly north along the west African coastline, with winds increasing between that line of low pressure and the high to the north. Good winds from the north east up to 30 knots have created conditions perfect for breaking race records and already leading yachts are more than a day ahead of leaders in the 1996 Vendee Globe.
This animated infra-red map courtesy of Intellicast clearly shows the powerful trough in the west Atlantic (red 'cloud' indicates very cold cloud tops, and usually a lot of rain at the surface) and the deepening high centred between the Azores and the Canaries (high pressure zones are indicated by dark blue). Winds circulating around this high pressure cell (clockwise in the northern hemisphere) are pushing the leading Vendee Globe yachts quickly towards the Inter-Tropical Convergence Zone. Where best to cross the tricky trough of low pressure is foremost on the skippers' minds. Eyes on the doldrums Now all eyes are focused on the ITZC and where best to cross it! Ellen MacArthur aboard Kingfisher aimed for a position 30 degrees west as she passed between the Canary Islands, and at the time the heaviest cloud activity along the ITZC was centred around 30 degrees west. She has stuck by her decision and is now the furthest west of any yacht. Catherine Chabaud (Whirlpool) and Dominic Wavre (Union Bancaire Privée) are furthest east, hugging the west African coastline, while the remaining front-runners are somewhere in between. It's a gamble Who's decision will pay off best? According to routing guru Bob Rice, the best place to cross the 'line' is where cloud activity is greatest. That's where opposing winds from both hemispheres are driving most deeply into the centre. Winds along the African coast, he says, tend to be light and variable as they become affected by the hot land mass to the east. It all sounds cut and dried, but in reality there are many variables. Perhaps Chabaud and Wavre are hoping that the ITZC will remain in the north along the eastern Atlantic and perhaps by crossing the line early they will be the first to enter the region of south easterlies circulating around the St Helena high pressure system. Hmmm ... So many choices, so many decisions. From where we sit, we reckon Kingfisher is in a good position, weather-wise. But any separation from this highly competitive fleet is always a difficult choice. Meanwhile, winds in the South Atlantic will provide plenty of challenges for these experienced sailors. The St Helena High is not well formed, with a trough of low pressure extending from Brazil well into the Southern Ocean. If skippers were hoping for a downwind ride between that trough and the centre of the St Helena High, they better start praying for conditions to change! Yacht positions Position of leading yachts courtesy of Virtual Spectator on November 18. Chabaud aboard Whirlpool is the yellow line to the east. MacArthur aboard Kingfisher is the blue line to the west and Parlier aboard Aquitaine Innovations is the green line in the middle. Another look at the weather Another view of the Atlantic in this image dated November 18. The ITZC is at the bottom of the image, shown as a line of cloud from west Africa to South America. Note the band of cloud east of Nova Scotia and the high pressure to the east of the trough. Also note how the isobars around this high are closer together on its western and southern flanks. The area of least wind is west of Gibralter and south of Portugal. Skippers in the Vendee Globe 2000 are enjoying steady winds from the north east as they head towards the Cape Verde Islands. This is a hint of what these sailors will look forward to in the South Atlantic. This image is dated November 17and shows a band of weak high pressure between southern Brazil and Namibia. The close-knit isobars of the roaring 40s are shown at the bottom of the image. To get to these constant winds, sailors have to navigate through the band of high pressure, located between the westerlies and the ITCZ. Trouble is ... there's no clear path - no place where winds circulating around the high (counter-clockwise in the southern hemisphere) take a dive to the south. If this pattern keeps up, skipper will have some head scratching to do. © weather-wise.com 2000 Explore comment from the |