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The 2020 Atlantic hurricane season is busiest on record as Subtropical Storm Theta forms

Theta is the 29th named storm of the 2020 Atlantic hurricane season

The National Hurricane Center’s map of active systems and systems to watch on Monday evening. (NOAA/NHC)
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In a move truly on brand for 2020, the Atlantic Ocean broke its record for the all-time busiest hurricane season Monday evening as a new subtropical storm formed and earned the name “Theta.”

The season had already featured 28 named storms, including a dozen that have made landfall in the United States. In addition to newly minted Theta, meteorologists are tracking yet another system in the Caribbean that could be named in the days ahead.

Tropical Storm Eta floods South Florida, could make second landfall late week

The 2020 hurricane season will be remembered not only for its sheer number of storms, but also the areas that were targeted by storms multiple times. Southwest Louisiana was ravaged by Category 4 Hurricane Laura in late August, only to be battered again by Hurricane Delta in early October and sideswiped by Zeta late in the month.

Mexico’s beleaguered Yucatán Peninsula also saw repeated storm strikes, with the area lashed by Gamma and Delta in early October, and then by Zeta as well.

Fortunately, Subtropical Storm Theta is likely to remain primarily out to sea — but another area of concern in the Caribbean may not be so innocuous. That one could affect Central America next week, but forecast confidence is very low.

Theta forms, establishing new Atlantic record

On Monday, the National Hurricane Center highlighted a cluster of thunderstorms about 750 miles southwest of the Azores, indicating it had a 70 percent chance of eventual development as it slowly drifted east. At 10 p.m. Eastern time, the Hurricane Center declared it a subtropical storm — meaning it had some of the characteristics of a tropical system, but also formed through partially mid-latitude processes.

On satellite imagery, the system is easily discernible as a swirl of cloud cover, which increasingly wrapped about its center on Monday evening. The disturbance initially formed as a “frontal cyclone,” or a wave of low pressure along a cold front. Cold air in the upper atmosphere allowed that low to develop thunderstorm activity, eventually pinching off from the front and forming a detached, closed circulation. As that process continues, Theta, while changing little in intensity, will probably become fully tropical in nature.

The National Hurricane Center also expects air exiting Theta’s thunderstorms at high altitudes to change the system’s upper-level circulation such that it is able to develop more tropical characteristics.

Theta is expected to pass between the Azores and the Cabo Verde islands late this week, while maintaining strength as a 50 to 60 mph system. Indications suggest Theta could make a run for Britain or become swept up in an even bigger mid-latitude ocean storm next week.

Caribbean threat

The first system to watch could affect the western Caribbean and has already been assigned a 50-50 shot of eventual development by the National Hurricane Center. One component of the fledgling system was over Puerto Rico and the eastern Dominican Republic on Monday morning and was producing heavy tropical downpours across the Island of Enchantment.

Puerto Rico and the Virgin Islands were under a flash flood watch until Wednesday evening, with a broad two to four inches likely to fall beneath a dense plume of tropical moisture. That river of soupy air is being drawn northward, spiraling into Tropical Storm Eta west of the Florida Straights.

Simultaneously, a weak tropical wave arriving from the east will tap into this moisture while getting some energy from a cold front arriving out of the northwest. This combination of atmospheric features will rendezvous this weekend, when conditions are favorable for a storm to form.

Down the road, it could potentially affect Central America. If it is named, “Iota” is the next Greek letter on the list.

Clinching the record

When Theta officially was named on Monday night, it meant 2020 had broken the record for the most named storms ever observed in an Atlantic hurricane season. The previous record of 28, which 2020 had already tied with Eta, was set in 2005.

That year was the only other year on record when forecasters had to dip into the Greek alphabet after having run out of traditional storm names. The 28th nameable system of the year in 2005, Zeta, formed Dec. 30. This year’s, Eta, did so Oct. 30 — exactly two months ahead of record pace.

There’s even a chance that, if the Caribbean disturbance develops, we could hit the 30-named-systems mark in the Atlantic, an unprecedented occurrence attesting to just how active and destructive this season has been. As of early October, the United States had been hit with three hurricanes that resulted in at least $1 billion in damage, a number that has increased since then.

Hurricane Eta exploded before hitting Nicaragua, but we may never know how strong it was

Unusually warm Atlantic waters and a La Niña event brewing in the tropical Pacific Ocean helped tip the scale toward an especially active season this year.

Several of the storms this year have undergone rapid intensification, which is linked to warming ocean waters from human-caused climate change. Meanwhile, the link between climate change and the number of storms is less clear, with some studies showing future seasons may have fewer but stronger storms.

What is apparent is that the combination of increasing coastal populations, climate change-driven sea-level rise and changes in storm characteristics, including increases in inland rainfall production, are all making hurricanes more destructive than they once were.

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