If you’re not a scientist, a person who follows the weather or a storm-tracker, then it might seem random: Why do some tropical systems turn into hurricanes, and why do others fall apart?
It’s not random -- there are actually three factors largely at play, according to this July 2020 report.
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Meteorologist Candace Campos said hurricanes can come in all different shapes and sizes, but there are a few things that need to occur consecutively for storms to live and remain healthy. Below are the top three factors that have a direct impact on the strength of a tropical system.
1. Warm ocean water
Think of hurricanes as a massive heat engine, transferring heat energy from the surface of the ocean and releasing it into the atmosphere, Campos said.
This process can’t begin until waters are hot enough to fuel tropical development. And that’s why hurricanes only form in tropical waters, where ocean temperatures are above 80 degrees. The longer a storm stays over water, the better chance it has to maintain or even strengthen further.
The only exception is if a storm becomes stationary. This will allow waters to churn up enough and cool down under the rain and clouds of the storm -- and this was the case with Hurricane Dorian in 2019.
The deadly major hurricane slammed its brakes over the Bahamas, eventually weakening over the cooling waters.
2. Wind shear
Wind shear in a storm is the change of wind speed or direction vertically through the storm.
If the wind is stronger toward the top of the hurricane (high shearing), the center column of the storm will become tilted. Think of a spinning top. If it spins directly upright, it maintains its speed, Campos said.
The moment the top begins to tilt, the spinning speed significantly drops. This goes the same for a hurricane: Any slight tilt to the center, will weaken or even destroy a storm. Lower wind shear, or evenly winds through the atmosphere, is what a storm needs to maintain its health.
3. Moisture content
Hurricanes are jam-packed with moisture. Campos said they’re similar to steam engines sucking up heat energy from the water into the belly of the storm. It’s the same way as runners staying hydrated during a marathon.
But this is not the ONLY source of moisture for storms.
They need plenty of available moisture in their immediate surroundings. If dry air is nearby, it has the potential to be sucked into the center of the storm. If dry air finds a way in, it will quickly erode the whole system and weaken the storm.
Although hurricane season runs from June 1 through Nov. 31, that doesn’t mean tropical development is impossible outside this time. As long as these three conditions align, a tropical system can develop any time of the year.