Rapid intensification: How hurricanes gain strength and why it's so dangerous

Rapidly intensifying tropical storms and hurricanes are especially dangerous because they can give the public less time to prepare and catch people off guard.

As the Atlantic hurricane season kicks into high gear with Francine tracking toward Louisiana, AccuWeather meteorologists are deeply concerned about the possibility of numerous storms undergoing rapid intensification across much of the basin. If this intensification occurs as storms near land, the threat to lives and property could significantly increase.

Rapid intensification refers to a process when tropical storms and hurricanes quickly become stronger. Specifically, it means a storm's wind speed increases by at least 35 mph within 24 hours. This phenomenon can cause a tropical storm to escalate into a hurricane or a hurricane to jump one or more categories in less than a day.

Rapidly intensifying tropical storms and hurricanes are especially dangerous because they can give the public less time to prepare and often catch people off guard. Predicting a storm's peak intensity and its intensity at landfall is one of the most difficult aspects of weather forecasting, and a rapidly intensifying hurricane adds tremendously to that challenge.

"The general rule of thumb is that people prepare for one category up on the AccuWeather RealImpact™ Scale for Hurricanes or the Saffir-Simpson Hurricane Wind Scale to allow for fluctuation in the strength of tropical systems," AccuWeather Hurricane Expert Alex DaSilva said, "However, a danger exists when a tropical storm or hurricane is undergoing rapid intensification, as the storm potentially could become much more powerful, dangerous and destructive than even that one-level buffer might account for."

The AccuWeather RealImpact™ Scale for Hurricanes goes beyond just measuring wind speeds; it takes into account a variety of factors such as coastal flooding, freshwater inundation, terrain, and the number of people affected. In contrast, the Saffir-Simpson Hurricane Wind Scale focuses solely on wind intensity.

When a densely populated area is in the path of a hurricane, more time is required for preparations and potential evacuations. For instance, a bustling city like New Orleans might need at least 72 hours of notice to prepare for a direct hit, as suggested by NOLA Ready. The larger and denser the population, the greater the urgency to ensure everyone is safe and prepared.

Unusually warm waters are a prime concern

Warm water is the fuel for hurricanes, and this season the ocean temperatures across the Atlantic have been in record territory. "We continue to notice incredibly warm waters over much of the key development areas in the Atlantic," DaSilva said.

When warm waters mix with other factors, such as low wind shear and an abundance of tropical moisture, the perfect recipe for rapid intensification is created. Not every storm will experience this sudden boost in strength, but when these conditions align, the likelihood increases significantly.

According to DaSilva, sea-surface temperatures across the Atlantic Basin are at their highest levels ever recorded for this time of year. The ocean generally continues to soak up heat from the sun through early September, although some temporary cool patches may form.

"The fear is that as we enter the heart of the tropical season—from late August to early October—the sea-surface temperature may continue to eclipse last year's record-breaking season," DaSilva said. "The warmer the oceans are, the more favorable the environment will be for tropical development and rapid intensification."

The depth of the warm water is the most important

As tropical storms and hurricanes pass over warm surface waters, the wave action produced by strong winds blowing on the ocean creates massive waves and upwelling, where water from the depths mixes with the surface. Most of the time, this will lead to the colder deep water cooling the surface water and then cause the intensity of a slow-moving hurricane to level off or weaken. When a hurricane moves quickly, this cool upwelling action is reduced as the storm will continue to encounter warm surface water.

AccuWeather meteorologists also look at the depth of the warm water or ocean heat content (OHC). The deeper the OHC, the less impact upwelling will have.

The potential for multiple rapidly intensifying tropical storms and hurricanes for the 2024 season includes threats from near U.S. coast developing systems in the Gulf of Mexico and off the southern Atlantic coast, as well as for areas throughout the Caribbean and the southwestern Atlantic. Formation near land and rapid intensification near land are the two standout situations that can cause quick changes to the forecasts and risks.

Top priorities when a hurricane is tracking to your location

AccuWeather Senior Meteorologist and long-time Florida resident Dave Houk had sound advice regarding hurricane preparedness.

"Staying up to date with the storm and following along with forecasts is the key to taking action and mitigating risks, as forecasts can change over time," Houk said. Residents and visitors need to have plans and preparations before the storm arrives and know what the "worst-case scenario" can mean for their area.

Storm surge inundation is the greatest danger people may experience during a hurricane. However, the stronger the hurricane winds or the faster a hurricane intensifies, the greater the potential magnitude of storm surge flooding and the chance that rising water may block a last-minute evacuation route.

Houk stresses that people need to be aware of their surroundings, such as whether they are near the coast, a bay or a river, where a storm surge can lead to rapidly rising water in their location and escape route. For example, an elevation a couple dozen feet above sea level may be safer than one only a few feet above sea level.

"Proper planning and preparation prevent panic when a hurricane suddenly forms nearby or undergoes rapid strengthening," Houk said. "If ordered to evacuate, is the emergency kit prepared properly? Based on the forecast track of the storm, should evacuation to an area to the north, south, east or west be best for minimal impacts?"

For those deciding to brave the storm, it's crucial to be aware of the severe risks involved. Beyond the immediate danger of rapidly rising floodwaters, there’s the threat of flying debris and falling trees that could severely damage or even destroy homes. Those who stay should be ready to face significant hardships, including days without electricity and fresh water. Additionally, the aftermath may bring debris and displaced wildlife, adding to the challenges of staying safe. Be prepared and stay vigilant—hurricane season is not to be taken lightly.