Coastal Processes FAQ - What's the difference between a northeaster and a hurricane?

Northeasters and hurricanes are both powerful storms that may exert significant impacts on Delaware's coastal areas. While hurricane season runs from June 1st through November 30th , northeasters are a year-round threat to coastal Delaware.

The primary differences between these two types of coastal storms include the location of storm origin and the wind speeds.

Hurricanes

Hurricanes and tropical storms are cyclones (low pressure systems with counter-clockwise circulating fields of wind) that originate in tropical areas. These storms are dependent on warm tropical waters (80 degrees or greater) as a critical factor for storm development. A tropical cyclone with wind speeds between 39-74 mph is called a tropical storm. When wind speeds exceed 74 mph, the tropical storm becomes a hurricane.

Northeasters

Northeasters are also counterclockwise-circulating fields of wind, but these cyclones form outside of the tropics in the mid-latitudes (they are extra-tropical cyclones). The northeaster season generally runs from October through March, but these storms can occur any time of the year. Northeaster winds typically exceed 30-40 mph with gusts above 60-74 mph.

Torrential Rains, Flooding, and Storm Surge

Hurricanes are unquestionably the more powerful of the coastal storms, but northeasters occur more frequently along the Delaware coast, have longer durations, and may impact much larger areas.

Hurricanes and tropical storms are notorious for dumping anywhere from five to ten inches of rain as they make landfall and then die away. Severe inland flooding occurs as a result of too much rainfall too fast. Rivers overflow their banks and spill into their natural flood plains. Urban flooding causes problems when storm drains become overwhelmed or even clogged by debris.

Northeasters can also bring rain in large volumes and long duration, which may cause extensive flooding in both coastal and non-coastal areas. However, along the shoreline, storm surge is the principal cause of flooding and inundation during a northeaster.

Storm surge is caused by the very low atmospheric pressure at the center of the storm (both hurricanes and northeasters) and the pulling of water onto the shoreline by winds accompanying the storm. The elevated water levels resulting from the storm surge moves ashore and floods adjacent land areas.

The flood height and duration of a northeaster can actually exceed that of a hurricane. The most severe storms in Delaware have been northeasters. The storm of record is the March 1962 northeast storm, which lasted through three days and five extremely high tidal cycles.