🔍 Key Concepts

• Dangerous vs. navigable semicircle of a Northern Hemisphere storm (relative to storm motion) • How wind direction and fetch affect wave and swell formation • Relationship between the rear/after sections of a storm and long-period swells that move away from the storm center

💭 Think About

• First, picture a Northern Hemisphere low and its direction of movement. Which side is called the dangerous semicircle and which is the navigable semicircle? • Think about where the wind blows with the storm’s motion, giving the waves the longest time and distance (fetch) to build, and where the resulting swells would be able to outrun the storm center. • Compare “front” vs. “rear/after” and “left” vs. “right” relative to the storm’s track. In which combination do you get the longest, most consistent fetch that can generate swells ahead of the storm?

✅ Before You Answer

• Verify which side of the storm track (left or right in the Northern Hemisphere) has winds reinforced by the storm’s motion. • Check how front vs. rear of the storm changes whether waves can move out ahead of the storm or are trapped within the storm field. • Confirm that long-period swells that outrun the storm must be produced where wind blows over a long fetch in nearly the same direction the swells will travel.