For the Instructor

These student materials complement the Coastal Processes, Hazards and Society Instructor Materials. If you would like your students to have access to the student materials, we suggest you either point them at the Student Version which omits the framing pages with information designed for faculty (and this box). Or you can download these pages in several formats that you can include in your course website or local Learning Managment System. Learn more about using, modifying, and sharing InTeGrate teaching materials.

Initial Publication Date: December 7, 2016

Extratropical Storms and Fronts

North of the Tropic of Cancer (23.5 N latitude) and south of the Tropic of Capricorn (23.5 S latitude) extratropical storms and weather fronts dominate as the major storm impact to coastal zones in these regions. Although not capable of packing the full magnitude of punch that a hurricane can produce, some storms outside of the tropics can produce wind speeds equivalent to those of weak hurricanes, resulting in very large waves and storm surges along coastal environments.

Northeasters

Along the east coast of North America, the classic example of an extratropical storm system is the Northeaster, which is a storm that tracks from the Midwest of the United States, northeast along the east coast of the United States and into Maritime Canada before being turned eastward into the northern Atlantic basin. The termNortheaster derives from the fact that the winds of these storms are from the northeast within this irregularly shaped but counterclockwise rotating storm system. They occur between late fall through spring when cold arctic air moving southeast comes in contact with warmer air moving north from more southerly latitudes to create a low pressure system with a cold center (in contrast to a hurricane with a warm center). Although not as strong as hurricanes, northeasters are larger in diameter and can impact three to four times as much shoreline as a very large hurricane. Further, their frequency of occurrence is higher for the east coast of North America with 20 to 40 annually, although only several of these generate severe offshore wave heights greater than 5 meters.

Fronts

There are numerous other types of weather systems that can affect coastal zones. The most common along the northern Gulf of Mexico is what is known as a front. A front is zone between two air masses with different temperatures, different levels of humidity, and densities. In the winter, low humidity,cold air systems sweep southward across North America and encounter more humid, warmer air over the Gulf of Mexico. A strong southerly flow (winds blowing from south to north) persists along the northern Gulf in the days prior to the arrival of the cold front. These sustained winds blow as much as 30 to 50 km/hr and can generated large waves in the Gulf of Mexico that then travel northward and impact the shore, leading to erosion, deposition and overall modification of the pre-frontal morphology. As the front passes, the wind direction shifts blowing from the north, bringing much colder and dryer air. These north winds can similarly reach sustained speeds in excess of 30 km/hr persisting for a couple of days. Because these winds are from the north, they can generate large waves in the bays on the north side of the shorelines and have been shown to be very effective at eroding the marsh and other features on the north facing shorelines of barrier islands and marsh platforms.