The eerie calm in the tropics:
HOUSTON – If you’ve been wondering why things are so quiet during the peak of hurricane season, you’re not alone.
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Over the past couple of weeks, I’ve been asked that question a lot. Sept. 10 marks the statistical peak of the Atlantic hurricane season; it’s typically the most active day for storms in the Atlantic, the Caribbean, and the Gulf.
Yet, in the last 75 years, this date has passed without a named storm only nine times, and this year joins that list. So, what’s happening? Click play, and I’ll walk you through it.
Here’s why there hasn’t been a named storm since Aug. 28:
We hear a lot about how warm the ocean is, but that’s only part of the story when it comes to hurricanes.
Think of a tropical storm or hurricane like a car, you need more than just gas to get it moving. A vehicle also needs good tires, a working battery, and all the right parts running together. The same goes for a storm.
Warm water is the fuel, but other key ingredients have to line up, too. Right now, several of those ingredients are missing, and that’s what’s keeping storms from forming:
- Sinking air over Africa: A large area of high pressure has set up over Africa, leading to sinking air. This limits the number of tropical waves that typically travel from Africa into the Atlantic and can become the seeds of developing storms. With fewer tropical waves and an already dry environment, the pieces just aren’t there to get the hurricane “engine” running.
- Dry, stable air in the Atlantic: The main development region is experiencing below average tropical moisture and instability. There’s just not enough fuel in the atmosphere to get storms started. The below graphic shows below average moisture in the main development region in the Atlantic, there is higher moisture closer to the U.S. and off Africa’s coast but little where it really counts.
- Strong wind shear: Higher-altitude winds are tearing apart any storms that try to get organized. There is a pronounced area of high wind shear shown in bold red on the graphic below that stretches across the Atlantic. This is critical because for a system to build into a tropical storm or hurricane, winds need to move in the same direction and speed from the ocean’s surface up through 5.000 feet in the atmosphere. Instead, opposing winds are ripping storms apart. This wind shear is caused by what is called a TUTT low or tropical upper-tropospheric trough. The troughs in the graphic below are the white arrows. This has been in place for the past two weeks.
How rare is this?
Looking back, this kind of quiet isn’t just rare, it’s almost historic. Since 1950, only once has there not been a named storm from August 29 through September 16. That year was 1992. Category 5 Andrew hit Miami that year. Similar to this year, Erin was an August Category 5, but it did not hit land. If we don’t get a storm in the next six days, we’ll join that exclusive club.
This pattern can’t last:
There is a small 20 percent chance that a tropical wave off Africa could develop into a named storm within the next seven days. But overall, high wind shear and dry air are expected to keep storm chances low for now. But by the end of the month, the current weather pattern we are in will change. All of the ingredients will be in place for a flurry of storms to form. We’ll keep you updated when this will happen.