Active tropics keeps spinning up systems as above-average season continues.

4 p.m. update: Tropical Storm Karen was downgraded to a depression Monday afternoon after a plane investigating the storm failed to find a center of circulation.

In its 4 p.m. statement, the National Hurricane Center said the storm's winds had dropped below the threshold of a tropical storm due to wind shear and dry air.

The storm could restrengthen after it crosses Puerto Rico and enters the Atlantic Ocean, weather forecasters said.

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A crowded tropical Atlantic added Tropical Storm Lorenzo this morning, a budding cyclone that joins tropical storms Karen and Jerry.

Lorenzo is on track to gain Category 2 hurricane strength later this week, but is in the far eastern Atlantic about 315 miles south-southeast of the Cabo Verde Islands.

None of the three systems are a threat to the continental U.S. at this point, but Karen is forecast to move over Puerto Rico as a tropical storm on Tuesday and start to make a left turn toward the east coast on Saturday.

“Such a track to the north is eerily similar to that which Dorian took earlier this year, when it passed through the eastern Caribbean at the end of August,” AccuWeather meteorologists wrote in a forecast. “Because of this, interests across the Bahamas and the southeastern United States should be carefully monitoring the track of Karen this week.”

University of Miami senior research associate Brian McNoldy is also keeping an eye on Karen.

He said in his column today that a strong ridge of high pressure is expected to build to Karen’s north in a couple of days which would force it west.

“The ridge is pretty robust in the models, so a continued westward track would bring it toward the Bahamas, Florida and/or the southeast US coast in about one week,” said McNoldy, who noted the system could fall apart before then or fall under the influence of a host of other environmental factors.

“At this long lead time, it’s just worth being aware of this ‘left turn’ possibility, and knowing that the global models and their ensembles have supported this scenario for a couple days now.

Jerry could take a swipe at Bermuda as a tropical storm late this week.

While the peak of hurricane season was marked Sept. 10, the tropics are forecast to remain active into early October.

Colorado State University researcher Phil Klotzbach said that Lorenzo is the 12th named storm this year, reaching the total for an average season with more than two months remaining.

“It should be noted, however, that five of the Atlantic named storms of 2019 so far have lasted one day or less (Andrea, Chantal, Erin, Fernand and Imelda),” Klotzbach said in a social media post.

Karen is barely hanging on as a storm this morning, with the National Hurricane Center calling it “disheveled.”

As of the 11 a.m. advisory, Karen had 40 mph winds and was moving northwest at 12 mph.

Tropical storm warnings are in effect for Puerto Rico, the US Virgin Islands and the British Virgin Islands.

Strong wind shear and dry air have been holding back development and Karen could weaken to a tropical depression later today.

But, upper-level winds are expected to become more favorable later this week, allowing some “modest” strengthening to occur.

By the end of the 5-day forecast, more significant strengthening is expected and Karen could be near hurricane strength at 70 mph by Friday.

“The predominant model consensus shows a ridge of high pressure building north of Karen late in the week, forcing the storm to track to the west towards The Bahamas,” said Weather Underground co-founder Jeff Masters. “In this scenario, the mainland U.S. could be at risk in about a week to 10 days – though the uncertainty in this outcome is high.”

Klotzbach’s special two-week hurricane season forecasts show the tropic as particularly feisty through at least Sept. 30 owing to weak wind shear and the passing of a the Madden-Julian Oscillation.

The Oscillation, or MJO, is a wave of storminess that travels around the globe regularly and can enhance tropical cyclones as it passes.