June 23, 2001 - Working Your Way around the Squash Zones and the Bombs

New Zealand is poised between the Roaring Forties and the Tropic of Capricorn. No wonder weather forecasting is more an art then a science in this part of the world.

During the summer months tropical depressions drift down onto North Island, pushing warm, wet northeasterly winds before them. In the summer, bone-chilling southerlies roll over South Island and up the Tasman Sea, bringing winds that were only recently passing over Antarctica.

Meanwhile high-pressure systems build over Australia and drift eastward across New Zealand. Where the lows and highs collide, squash zones occur, producing winds 50 percent stronger than would normally be generated. You will not be able to predict this by watching the barometer--you need to look at the isobars. Occasionally a low gets truly caught in the middle and "bombs", creating a fierce system with winds of 50 knots or more.

So when should you leave? It is tempting to leave in April because you maximize the time you have to cruise the islands and it is also still warm in New Zealand. However you risk being caught in a late tropical depression. Lows forming in the tropics are heading south--toward you--and there is not much you can do to avoid the ensuing headwinds.

Advice from those who have made this passage several times before is leave later rather than earlier. By June the lows are coming up from the south rather than down from the tropics. You can see them forming off Antarctica and track them as they head north. Rarely do they make it north of 35 degrees South. Leaving late may make the first few nights at sea rather cold, but it just makes you appreciate the warmth more as you travel north.

Stay tuned in the coming weeks for weekly reports from THETA VOLANTIS as Colleen and Ryan sail to Tonga, Samoa, and beyond.

For more info on forecasting and analyzing marine weather, see Mariner's Weather Handbook by Steve and Linda Dashew. Also, check out Surviving the Storm: Coastal and Offshore Tactics, for tactics you should know if you get caught in heavy weather. For further research, see the Heavy Weather section of SetSail.com.