Tropical storms and hurricanes can face multiple obstacles as they travel across the vast expanse of the ocean. Sometimes those factors are just a speed bump in their life cycle, while others can lead to the storm’s demise.
Here’s a look at four potential nemeses of tropical storms you might hear meteorologists mention when explaining the forecast for each storm and what they mean.
1. Wind Shear
-Big Picture: Wind shear is the change in wind speed and direction with height. It’s often a hostile factor that can tilt or even rip apart tropical storms and hurricanes. So, you could have a storm over a region with very warm water, but if it’s getting hammered by wind shear for an extended time, the storm might struggle to intensify or even meet its demise.
-A Caveat: Sometimes wind shear close to a storm that would normally be unfavorable can actually have the opposite effect if it’s in the right location. We’ve seen several cases in the past where wind shear was located just far enough west of a hurricane to not disrupt its core, but instead help ventilate the storm and allow it to intensify. In 2018, Hurricane Michael’s rapid intensification into a Category 5 before making landfall along the Florida Panhandle was aided by that type of setup.
2. Dry Air
-Big Picture: Since tropical storms and hurricanes need persistent thunderstorm activity in order to stay healthy, any dry air they encounter along their path can be an obstacle. That’s because dry, sinking air suppresses thunderstorms and strengthens their downdrafts (downward moving air) of storms that are able to form, causing them to weaken quickly.
-A Caveat: We saw dry air become a speed bump for the intensification of what would become Hurricane Francine in early September 2024. For a time, dry air infiltrated the tropical storm’s center, preventing it from significant intensification.
Eventually, Francine fended off this dry air, allowing it to intensify into a strong Category 2 before making landfall in Louisiana.
So on occasion, dry air can be an obstacle for only a period of time during a hurricane’s life cycle, while other times it can lead to a storm’s weakening and cause it to fall apart.
3. Land Interaction
-Big Picture: Hurricanes get their fuel from the oceans, so when they track over land, it triggers weakening because it’s cut off from that warm, moist air source. The weakening can be minimal to major, depending on the length of time spent crossing a land mass.
Whether the land has tall mountains or not also plays a role. For example, the mountainous terrain of Haiti and the Dominican Republic in the Caribbean can inflict a great amount of weakening, and some past storms have even fallen completely apart.
-A Caveat: Sometimes this weakening from land interaction can be just a speed bump along a hurricane’s path.
Hurricane Beryl in July 2024 is an example of this. After making landfall in Mexico’s Yucatan Peninsula as a Category 2, it weakened to a tropical storm once it reached the Gulf of Mexico. Since the Yucatan is rather flat land, it did little to disrupt the overall circulation of Beryl, allowing it to reorganize into a hurricane just before striking Texas, where it caused significant wind damage.
One other thing to consider is that while land interaction might be good news for locations along the potential future path of a storm, it’s bad news for the land area causing the weakening.
4. Cooler Water
-Big Picture: Hurricane’s draw their energy from the heat and moisture of the ocean, which helps them to maintain or gain strength. How deep that warmth extends below the ocean’s surface matters as well, which is called oceanic heat content.
A storm tracking through an area with lower oceanic heat content compared to average might tip the scales toward less intensification in the tropical Atlantic, Caribbean or Gulf of Mexico. Cooler ocean water can also cause the atmosphere above it to become more stable, or less conducive to strengthening.
Hurricanes that stall can sometimes generate their own cool water through a process called upwelling, where strong winds in the storm churn up seawater, causing cooler water from below to rise and mix with surface water. If the hurricane is barely moving, this upwelled cool water can zap its energy source a bit.
-A Caveat: A brewing storm that might initially struggle to intensify over a part of the Atlantic that contains less oceanic heat content can track toward another location where this ingredient is more favorable. If that happens, then a fledgling tropical depression or weak tropical storm we might track for days can suddenly grow stronger, assuming wind shear is low and the atmosphere is moist and unstable.
Chris Dolce has been a senior meteorologist with weather.com for 15 years after beginning his career with The Weather Channel in the early 2000s.
