The 2020 hurricane season is getting underway with a potential disturbance in the western Gulf of Mexico. There’s broad area of low pressure over Central America, technically called a Central American Gyre – a gyre being a large rotating weather system, with the emphasis on large. The giant disturbance overlaps into the Pacific Ocean, the extreme western Caribbean Sea and the southern Gulf of Mexico.
Sometimes, a tropical depression or storm forms in one of these bodies of water when part of the gyre breaks off into a smaller system. One such storm – Tropical Storm Amanda – formed in the Pacific over the weekend and moved into Guatemala.
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Computer forecast models indicate that Amanda’s remnant circulation might redevelop into an organized system as it rotates around the “mother” circulation of the gyre into the extreme southern Gulf of Mexico in the next couple of days.
The specifics vary with the model and the various updates. For now, it’s an Area to Watch. The details are impossible to predict, but the atmospheric pattern appears conducive for a storm to develop over the warm water of the southern Gulf.
It doesn’t appear that this system would affect South Florida. High pressure has moved over the peninsula from the Atlantic, and should block anything from coming this way.
Late in the week, some long-range computer forecast models show a second organized tropical system breaking off from the gyre and moving north in the western Gulf. It’s unclear if that circulation would be the same one that started as a remnant of Amanda, or some other disturbance that hasn’t yet formed.
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Looking at the details of forecasts of systems that don’t yet exist is a waste of time. The bottom line is, the entire western Gulf is an Area to Watch for a second development late this week into next weekend.
Looking back, it was an interesting May in the tropics – or, more correctly, the subtropics. Arthur and Bertha came and went, and briefly, it looked like we might get Cristobal. If the big low-pressure system in the Atlantic east of Bermuda had been able to wrap up a bit more and develop thunderstorms near the center, it would have met the criteria to be named a Subtropical Depression. But it wasn’t to be.
If something develops in the western Gulf this week as expected, it will be named Cristobal (pronounced krees-TOH-bahl).
If Cristobal had formed last week, it would have been the first time we had three storms officially meeting the naming criteria in May. But two is not terribly unusual – it’s happened several times that we know of. In fact, in 1908, two hurricanes formed in May. One hit the eastern Caribbean Islands and the other hit eastern North Carolina.
The important takeaway, however, is that these storms say nothing about how hurricane season is going to develop. The weather pattern that formed Arthur and Bertha was the same one that brought the torrential rain to South Florida. They were caused by a winter-like system meeting tropical air.
Since the triggers for Arthur and Bertha had a winter component, the busy May doesn’t say anything about the true tropical season to come in August, September and October.
The agencies and organizations that make hurricane-season forecasts are mostly calling for somewhat above-average activity. There are no obvious factors to tamp down the development of tropical storms and hurricanes this year, but no clear factors to make the season hyperactive either. Which raises the question, “What is average?” The answer is a bit murky.
Over the long term, an average season had 11 or 12 named storms. But more recently, normal has been 14 or 15. Our higher-resolution satellites and other modern mechanisms for measuring storms is probably responsible for at least a couple of additional names each year. So don’t get hung up on specific numbers. There are a lot of moving parts.
The bottom line: Assume it will be an active season. Which means, as always, we have to be ready. The COVID-19 crisis makes it more essential that we don’t all run to the store when a storm threatens. Think it out now. Let’s not make this situation any worse.