Hurricane Safety and Preparedness

Why Small Tropical Storms and Hurricanes Can Be Difficult to Forecast

At a Glance

Smaller tropical storms and hurricanes can be difficult to forecast.
They can intensify or weaken quickly.
Wind shear, dry air and land interaction can cause small storms to fall apart quickly.

Tropical Storm Dorian is the latest example of why small tropical storms and hurricanes are notorious for giving meteorologists an added forecasting challenge, particularly when it comes to predicting intensity.

The National Hurricane Center (NHC) reinforced this early Monday morning by saying, "Due to the wide range of the model solutions, the NHC intensity forecast remains of low confidence. It should be noted that compact tropical cyclones like Dorian are often challenging to predict."

(MORE: Latest Forecast For Dorian)

There are several reasons why smaller storms like Dorian can introduce additional forecast difficulties.

For one, tiny storms can rapidly strengthen or weaken due to small changes in their environment because they contain less mass (air, water vapor, clouds) to spin up or slow down.

One example of a storm that was able to spin up quickly because of its small size was Hurricane Humberto in 2007. Humberto first became a tropical depression at 4 a.m. CDT on Sept. 12, 2007. It then rapidly intensified and made landfall near High Island, Texas, as a Category 1 hurricane about 19 hours later.

Radar showing the rapid development of Humberto from a tropical depression into a landfalling hurricane with a well-defined circulation center in less than a day.
(National Weather Service)

But there are other cases when the fragile nature of smaller storms contributes to a quick demise, especially if the circulation center is poorly defined.

Two of the biggest factors that can trigger weakening or even the dissipation of a small tropical storm or hurricane are wind shear and dry air.

Wind shear is a change in wind speed and/or direction with height that can rip apart a tropical storm or hurricane.

Dry, sinking air disrupts tropical storms by suppressing thunderstorms and strengthening downdrafts of storms that are able to form. That prevents thunderstorms from persisting long enough near a surface low-pressure center in order to keep the storm healthy.

Danny in August 2015 was a small hurricane that quickly succumbed to wind shear and dry air. After becoming a Category 3 hurricane with 125 mph winds in the central Atlantic, it dissipated about 72 hours later near the Caribbean.

In 2015, Danny fell apart three days after becoming a Category 3 hurricane with 125 mph winds.

Land interaction is another trap that smaller storms must avoid to survive. The tall mountains of Hispaniola (Haiti/Dominican Republic) are one of the more notable features in the Caribbean that are capable of quickly shredding a small circulation.

While large and more intense hurricanes are not immune to the obstacles mentioned above, they are better suited to fend them off.

Sometimes, larger hurricanes will battle one or more of those hostile factors for a period of time and eventually reorganize. Other times, they can fall apart just like their smaller counterparts.