As we move toward the peak of the Atlantic hurricane season, particularly in August and September, the area meteorologists monitor expands significantly. We’re no longer watching only the Caribbean and areas near the U.S.; this is also when stronger tropical waves emerge from Africa and travel westward across the Atlantic. We have certainly seen several waves coming out of Africa, but so far none have made it to the Caribbean or developed into a tropical system.
On average, a tropical wave moves west at about 15 mph. If we could remove the atmospheric and oceanic factors that cause a system to strengthen, weaken, or change direction, a wave moving at that speed would generally take about 12 to 14 days to reach the U.S. coast, according to Dr. Robert Hart at Florida State University.
Once a system reaches the Lesser Antilles, that timeline is roughly cut in half, with about five to six days to reach the continental United States. Tropical systems that form closer to land offer even less time. A system developing in the Gulf of Mexico could reach the U.S. or eastern Mexico in just one to three days. Therefore, tracking a tropical wave from Africa can feel like a marathon.
Did you know?
Tropical waves play an important role in transporting moisture westward from Africa and across the Atlantic. Without them, the Caribbean would be a desert.
What are the chances of a far-off brewing system striking the U.S?
With a system moving closer, the chances of striking the U.S. also increase. But probabilities also change depending on a system’s location and intensity. A hurricane that has already formed over the tropical Atlantic, such as near the Cabo Verde Islands, has less than a 10% chance of eventually striking the continental United States. Once a tropical cyclone reaches hurricane strength, with maximum sustained winds of at least 74 mph, it is more likely to recurve and remain over the Atlantic. Once a system enters the Caribbean and becomes a hurricane, however, its chances of striking the Lower 48 increase to roughly 30% to 40%. Depending on its location and track, the risk of impacts elsewhere in the Caribbean can also remain moderate to high.
