East coast - wave direction and beach sand movement

[Stephen Tashi]

In the Great Courses lecture series "Oceanography", Prof. Tobin says that the general direction of beach sand movement ("sediment transport") along both the east and west coasts of the USA is from north to south. On the east coast, this is because the prevailing direction of waves is from the northeast.

Why is prevailing direction of waves from the northeast?

That direction is counterintuitive to me because my understanding is that the prevailing surface current ( the "north Atlantic gyre") would be from south to north along the east coast of the USA and this gyre is due to the prevailing winds (the "westerlies") which would be blowing from the southwest.

 

[PhanthomJay]

The direction of ocean currents are often different than the direction of waves. There are many factors that influence the direction of the currents, and yes, on the east coast of the US, the prevailing winds are westerly or southwesterly, at the mid to upper levels of the atmosphere, but at the surface ocean, waves are driven by surrface winds, which during large storms like hurricanes and winter storms and the like, winds at the surface are generally northeasterly, causing huge waves and costal flooding and migrating sand erosion moving north to south. It is somewhat analogous to winter storms called "northeasters", during which although general storm motion is SW to NE, driven by the jet stream level winds,
local surface winds are generally NE to SW, driven by surface pressure gradients, hence the name "northeaster' and the large waves generated moving from the northeast.to southwest.

 

[AlexTheParticle]

There are a few reasons why the prevailing direction of waves on the east coast of the USA is from the northeast. One factor is the Coriolis Effect, which is caused by the rotation of the Earth. This effect causes winds and currents in the Northern Hemisphere to veer to the right, resulting in a clockwise circulation pattern. This means that winds blowing from the southwest will actually create waves that travel from the northeast.

Another factor is the geography of the east coast. The coastline of the eastern United States is oriented in a north-south direction, which means that waves coming from the northeast will be more likely to hit the coast at a perpendicular angle, resulting in more erosion and sediment transport.

Additionally, the Gulf Stream, a warm ocean current that flows along the east coast, can also influence wave direction. The Gulf Stream flows from south to north, but as it reaches the coast, it begins to veer eastward, resulting in waves that travel from the northeast.

It's important to keep in mind that while the prevailing direction of waves on the east coast may be from the northeast, there are still other factors at play that can influence wave direction and sediment transport, such as storms and local topography. The east coast is a dynamic environment, and it's important to consider all of these factors when studying beach sand movement.