When to Go Left (in the Southern Hemisphere)
Last month we looked at “the law of storms”. Basically, this can be summarised that the way to go, to evade the roughest weather in a depression, is to the right of the incoming wind.
However, when your voyage involves encountering a passing trough or frontal zone then the best thing to do is to go left and sail directly into the approaching rain. By so doing we MINIMISE the time spent in the peak conditions of the trough. This is a case where the way to go is on a starboard tack, the opposite to the law of storms
MetBob. Bob McDavitt is the weather guru that uses /\/\etBoB to provide meteorological information for cruising sailors, primarily for those in the South Pacific.
1: In the case above we intend to sail to the north but have an incoming trough approaching from the west. The barometer is falling and “law of storms” suggest we go east. But in this case the better direction to go is to the left in steps, first to NW. then to W and maybe to SW.
Decode
Along path: Red barbs and arrows show forecast winds and current-one barb is 10 knots and half is 5, add 40-50% to get gusts. At map time: Black lines are isobars; streamlines are average winds. Purple arrow/shading are mean wave height/ direction. Blue/ Green//Red shading for rain. Black arrows show the currents.
2: Above, around 22hours later, position circled.
As the wind increased, we turned more to the left, to the west. Soon we will be captured by the rainy part of the front and maybe in NW or westerly winds. In these we turn more to the left going to the SW — a dogleg.
3: Above, around 14 hours later.
When the rain stops and the backing wind is from WSW, near position circled – yippee–we have got to the other side of the passing trough and we can resume our trip northwards with wind on port (as prescribed by the “law of storms”).
Bob McDavitt – check my other blogs at www.metbob.com