Key Points on Hurricanes

Hurricane Matthew in October 2016 (Source: NOAA)

This hurricane season has been one for the record books with several record-setting storms including Hurricanes Alex, Matthew and Nicole.  Florida also had its first landfalling hurricane since 2005 (Hermine), which ended a record streak without one.  Several keys points are worthy of discussion to clear up common misconceptions.

Issue 1: What is the difference between a hurricane and a “post-tropical cyclone?”

Tropical storms and hurricanes are warm-core systems that develop in the tropics.  They have a different structure than mid-latitude cyclones (such as Nor’Easters) that tend to develop along thermal boundaries in baroclinic zones.  Nor’Easters develop during the winter months along the U.S. East Coast in between the warm Gulf Stream and cold Atlantic coast.  Hurricanes, meanwhile, require warm ocean water to develop (typically at least 80 degrees F).  Mid-latitude cyclones typically have a much larger diameter (1,500 km to 5,000 km) than tropical storms or hurricanes (200 km to 1,000 km). 

As hurricanes move northward over cooler water, they lose their tropical structure and become “post-tropical cyclones.”   That means they more closely resemble a mid-latitude system than a tropical system.  A good example of this was Hurricane Sandy in 2002.  Although Sandy still had hurricane force winds and caused significant coastal flooding, it had lost its tropical characteristics shortly before making landfall in New Jersey.  National Hurricane Center meteorologists said afterwards that if a similar scenario arises in the future they would keep the hurricane warnings in effect so people wouldn’t think the danger had passed.

Issue 2: Why is the “cone of uncertainty” so important in hurricane forecasts?

A hurricane spans hundreds of miles across and its effects reach far beyond its center or “eye.”  That’s why it’s critical that people take the proper precautions when a tropical storm or hurricane threatens their region, even if the center doesn’t make landfall.  A great example of this occurred last month with Hurricane Matthew, which tracked just east of the Florida coast.  Although Matthew’s eye remained offshore, heavy rains, high winds and storm surge pummeled much of Florida.  The “cone of uncertainty” refers to where the center of the hurricane could be at a given time, but doesn’t take into account the size of the storm.

Issue 3:  What do meteorologists mean when they say the stronger part of the hurricane is on the right or east side of the storm?

Meteorologists often remind people that the strongest part of the hurricane is its right side.  However, the right side of the hurricane depends on the direction it’s moving.  For example, if a hurricane is moving west, then the right side would be the north side of the hurricane.  If the hurricane is tracking northward, then the right side would be its eastern side.  The stronger part of the hurricane is the east side because its motion contributes to the wind velocity.  National Hurricane Center scientist Chris Landsea explains that a “hurricane with 90 mph winds while stationary would have winds up to 100 mph on the right side and only 80 mph on the left side if it began moving (in any direction) at 10 mph.”

Please remember when listening to a hurricane forecast that hurricanes are a few hundred miles in diameter and not just a single point.