What Is The ITCZ And Why Does It Matter?

What Is The ITCZ And Why Does It Matter?

- Robin Urquhart

We were warned about the Intertropical Convergence Zone (ITCZ) well before we left on our Pacific crossing. It was constantly brought up in discussions with other cruisers. We were given strategies for getting through as quickly as possible and cautioned by tales of voyagers from previous years who had not been so lucky. “Took years off my life,” was how one sailor described ghosting through thunderstorms.

So, it was with no small degree of trepidation that we began our approach to the ITCZ. We checked weather forecasts religiously. The ITCZ seemed to jump all over the place: One day it was at 8° N and the next 5° N. We stayed north and went farther west than we had originally intended in order to stay above it. At 10° N, 131° W, we saw it starting to drop and ducked south. We were lucky — the ITCZ stayed a few degrees ahead of us the whole way down to the equator, at which point it jumped right over us and set up at 6° N again. We were through without having to cross it. In a way I was disappointed, but in another and more honest way, I was very relieved. It was as much luck as it was route planning.

The experience raised a few questions: What exactly is the ITCZ, why are sailors so afraid of it and why is it so hard to predict?

In order to understand the ITCZ, it is important to understand a little about pressure and wind. Wind is nothing more than the movement of air from high pressure to low pressure.