Approaching to the ITCZ

Sea Dragon is now really heading south, towards the Equator and tropical weather. There is more to sailing a boat in the tropics than warmer air and fair skies. The increased heat energy drives greater evaporation, and in most cases, humidity. Felt solar energy increases significantly and will soon become more important than actual air temperature for the crew. Perhaps more significant for travelers in this region than the static Equator is the ITCZ. This "Inter Tropical Convergence Zone" is often referred to as the solar Equator. As the sun progresses north (or south) of the Equator on its annual cycle, the area of greatest solar energy moves along with it. Lagging a bit (about one month) this area of ocean surface water is the hottest, most energized area of sea surface. As such, it generates a powerful band of rising air, or convection. This creates very low surface winds...the doldrums...and lots of weather. Rising air fuels squalls and often towering thunderheads. While the winds are localized and short lived, they can be powerful. Such venting drives lightning storms, and squally winds. While not as powerful as big thunderheads on land, these compact storms generate often the only wind in the region.

If you look at the attached satellite image taken from today, you can actually see the ITCZ. It's that band of east-west clouds just north of the Equator. That is the area Sea Dragon will have to punch through.

The ITCZ is the dominant feature that the crew must now navigate through. The trick is to pick a slot through the band that avoids major convection (squalls) but at the same time takes advantage of any wind they do generate. Sailing here is tricky and unpredictable. Winds can come from virtually any direction, accelerate with little advanced warning, and drop off to zero in just a few moments. Sail changes and a lot of active steering are in order. Like some giant chessboard, the crew will watch these cells moving and do their best to set a course through the maze of rising air cells. Seeing the building clouds, feeling the wind, and watching on radar for rain bands will help them do this. We also pull down satellite imagery that give us the big-picture view of the ITCZ band.

Right now this ribbon of unstable air runs SW from about 7N off the coast of west Africa, to just north of the Equator as it approaches the Brazilian coast.

Once through to the other side, the crew will truly have passed from winter...to summer. The SE trade winds will then gradually pick up increasing the boat speed to Brazil.

Ron Ritter