For the first time since 2014, no named storm formed in the Atlantic before June 1 — although Tropical Storm Alex almost kept that streak going. Does that give any clues as to the rest of hurricane season? No. That’s one of many questions I get annually, along with questions about subjects people fear could make hurricane threats larger, or subjects people hope could shrink the possibility of storms. Here are some of the most recent topics.
Start with La Niña, when the eastern Pacific is a lot warmer than average. La Niña somewhat shifts steering winds around the globe so average wind shear lowers in the Atlantic. Low wind shear increases the odds of a tropical storm or hurricane. We are in a La Niña.
Who’s loopy? The Gulf of Mexico Loop Current is a current of warm water that flows from the western Caribbean through the Yucatan Channel, extending northwestward into the central or northern Gulf, before looping clockwise to head southeastward through the Florida Straits, and then up the eastern seaboard as the Gulf Stream. Sometimes the pool of warmer-than-average water within the Loop Current breaks off and meanders in the Gulf. When tropical storms or hurricanes cross the Loop Current, they commonly strengthen from the enhanced warmth. Hurricane Katrina was an example of that, but it was an extreme example.
A marine heatwave is not a military training exercise. It is a heat wave over ocean water when stagnant high pressure, light wind and sunshine cause ocean temperature in a region to warm, especially after a recent storm stirred up the water. It builds over many days and may last for weeks. A marine heatwave preceded Hurricane Sally.
What the dust? Saharan dust is what many of us hope for unless you have respiratory issues. The reason we want it is the dust particles that travel thousands of miles westward across the Atlantic are known to suppress or limit tropical development.
A recent study showed cleaner air, with fewer pollution particles, has probably increased the number of tropical systems in the Atlantic in the last several decades. More sunlight reaches the ocean to warm it while steering winds shift to reduce wind shear.
There are caveats to all of the above. La Niña does fade over months, although when it fades or even starts is not very predictable. Marine heatwaves do break. The Loop Current weakens, disappears and reappears. Saharan dust and its influence is temporary, although it does cross the Atlantic in waves. The study about air pollution is just one of the dozens of different studies that show how various factors play a role in long-term tropical development. Don’t count on any one of these to make, shake, break or brake a hurricane. The ingredients for a hurricane of warm water, light wind shear and regions of low pressure are the things to watch throughout hurricane season.
Alan Sealls is chief meteorologist at NBC15 and an adjunct meteorology professor at the University of South Alabama.
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