Dave Kneale/Volvo Ocean Race
Cape Town, Saturday 15 November 2008
Warnings and Advisories: There are no relevant warnings or advisories for the course area today. However, you should continue to monitor the local South African Weather Service for any additional warnings or advisories.
SYNOPSIS: After a week of strong winds, high pressure is moving east into the course area for the weekend. As a result you can expect lighter winds and mostly sunny skies for the start.
Looking a little closer, the large area of high pressure is currently sitting just west of the course area, while a trough of low pressure lingers in eastern South Africa. As a result, the pressure gradient will stay out of the south today, but it will ease notably for this morning. Meanwhile, clear sunny skies and increasing temperatures may build enough of a thermal gradient to influence the breeze in the afternoon. In addition, the upper level flow is still strong enough that some gusts (into the mid 20s) may mix down for the afternoon.
Beyond the start, the winds are expected to back slowly at first. The fleet may see a light patch as they sail through the shadow of Table Mountain; however, as they clear the Cape, both the winds and the seas are expected to build.
Forecast Discussion: Light and variable winds are expected this morning. The winds will build slowly out of the S between 0900 and 1100. The sooner the winds build the more wind speed you can expect in the afternoon. By noon you can expect winds from 10-12 knots out of the S. Then for the afternoon look for the winds to increase to the high teens, with some gusts building into the high 20s.
Weather: Overall you should have a clear and sunny day. You may see some clouds developing over the mountains or along the shore for the afternoon. These will be fair weather clouds and will have little influence over your conditions. Look for the temperatures to increase quickly with clear sunny skies. The daytime high should be in the mid 20sC.
HEDGE: Forecast Confidence -Average.
1. There has been good model agreement for light winds on Saturday morning for some time now. However, there are two areas of concern with this forecast: the rate at which the wind speed will increase in the afternoon, and how much of a wind shadow Table Mountain will cause for the start area.
2. Look for the winds to fill between 0900 and 1100. Early morning you may see winds shifting all over the place but before you see any significant build, you can count on the winds shifting to S'ly. Through the day you may see oscillations between SE and SW, but the winds will primarily stay out of the S.
3. The slower the winds are to fill the less velocity you can expect. If the winds fill by 0900, you may see gusts into the high 20s. If the winds are slower to fill, you can expect the winds to stay in the high teens with gusts to over 20 knots.
4. The wind shadow from Table Mountain will extend north and west from the harbor area. The more SE'ly the winds the further west the shadow will extend. The best breeze may be in the eastern most part of Table Bay and north of Robben Island. In the wind shadow the fleet may see their winds drop to under 5 knots.
5. Once the fleet gets out of Table Bay and the shadow of Table Mountain, they can expect increasing seas (up to 4m) and building winds. The winds could easily be in mid 20s through the first night.
For those folks staying in Cape Town: Sunday and Monday will see light to moderate winds. You can expect the S'ly flow to persist through the weekend and into next week. On Sunday, look for 10-15 knots of breeze through the day. Sunday will see a little more build with winds in the 15-20 knot range. The temperatures will remain very mild with mostly sunny skies, and the daytime high will reach into the mid 20s C.