Karen becomes the Atlantic’s northernmost named storm on record » Yale Climate Connections

Three storms — two tropical, one subtropical — were plowing across the Atlantic and eastern Pacific on Friday. None is expected to become a hurricane, but one of the tropical storms was bringing torrential rains and localized flash flooding to the Northern Leeward Islands, while the other could do much the same across parts of the U.S. Southwest this weekend. And a non-tropical storm could end up being the biggest U.S. weather maker of the bunch as it brings high winds, heavy rain, and potential major coastal flooding from the Carolinas to New Jersey.

Jerry drags heavy rain across the Northern Leewards as it pulls away

Even as it remained highly disorganized, Tropical Storm Jerry was hauling enough moisture across the Northern Leeward Islands to dump huge amounts of rain even after much of the storm’s circulation had moved well north of the islands. As of 11 a.m. EDT Friday, Jerry’s diffuse center was located about 140 miles (225 kilometers) north of the Northern Leewards, heading northwest at 16 mph (26 km/h). Jerry’s top sustained winds were 50 mph (85 km/h).

Strong westerly wind shear kept Jerry asymmetric for most of this week. The shear was decreasing somewhat on Friday, but nearly all of Jerry’s intense showers and thunderstorms (convection) were still located well south and east of the storm’s ill-defined central circulation. Jerry’s sprawling yet sloppy structure meant it couldn’t take full advantage of ample deep ocean heat content and unusually warm water for early October (sea surface temperatures of 29-30 degrees Celsius or 84-86 degrees Fahrenheit are about 1°C or 2°F above average).

]Still, the warm waters have helped bolster Jerry’s convection, leading to torrential rains over several islands. Totals on Friday may approach 4 in (100 mm) as far south as Guadeloupe. As of 2:30 p.m. EDT Friday, a rainfall total of 5.89 in (149 mm) was reported at Barbuda, with sustained winds of 54 mph and gusts to 83 mph, according to Puerto Rico broadcast meteorologist Ada Monzon. Amounts in the 4-6 in (100-150 mm) range could also hit eastern Puerto Rico, where CoCoRaHS reports showed 1-2 in (25-50 mm) had already fallen at several stations by Friday morning.

As a double-barreled upper low along the U.S. East Coast helps steer Jerry northward, the storm will pass over some of the water overturned by hurricanes Humberto and Imelda a few days ago, further nicking its chances to intensify. It now appears Jerry is unlikely to organize or strengthen much before it turns sharply east, well south of Bermuda, by late in the weekend. That said, it wouldn’t be a total shock if Jerry were to make one last attempt at reaching hurricane strength around Sunday or Monday, as suggested by the HWRF intensity model.

Priscilla’s remnant rains heading for a parched U.S. Southwest

Tropical Storm Priscilla was on its last legs Friday over the northeast Pacific. At 11 a.m. Friday, Priscilla was centered about 195 mi (315 km) west-southwest of Cabo San Lazaro, Mexico, drifting north at 5 mph (7 km/h) with top sustained winds of 45 mph (75 km/h). Wind shear on Friday was pushing dry air into the storm and shunting Priscilla’s convection well east of its center. That decoupling trend is expected to continue, and by Friday night, Priscilla is predicted to become a remnant low.

As the rich moisture from Priscilla streams northward on Friday and Saturday into the higher terrain of the U.S. Desert Southwest, torrential rains and localized flash flooding are a significant concern. The amount of precipitable water (moisture in the atmosphere) above Flagstaff, Arizona, at 8 a.m. EDT Friday was measured by balloon-borne instruments at 0.97 inches (2.46 centimeters)—the highest amount ever recorded this late in the season in northern Arizona across 64 years of observing. Intense downpours could extend into parts of southern Nevada and Utah as well as southwest Colorado and southeast Arizona, with flash flood watches out across the entire region.

One silver lining will be some measure of drought relief: most of the area remains in the grip of severe to extreme drought, according to the latest weekly installment of the U.S. Drought Monitor.

Subtropical Storm Karen revs up in the midlatitude North Atlantic

Subtropical Storm Karen will have little impact except on the annals of Atlantic hurricane history. Karen became a named storm at 11 p.m. EDT Thursday while located at 44.5 degrees north, 33.0 degrees west, or about 545 miles northwest of the Azores. That made it the northernmost system in Atlantic history to be designated as a tropical or subtropical storm by the National Hurricane Center.

It wasn’t warm waters that nurtured Karen – sea surface temperatures were only around 19 degrees Celsius (66 degrees Fahrenheit) at the time – but rather a favorable pocket within a much larger mid-latitude storm system that allowed Karen to consolidate its convection and carve out a closed center of circulation. By Saturday, Karen is expected to lose that center of circulation and become post-tropical itself, remaining safely in the remote North Atlantic all the while.

NHC didn’t start naming subtropical storms until 2002. The runner-up for northernmost named storm in the Atlantic behind Karen during this post-2002 era was Tropical Storm Grace, which developed northeast of the Azores on October 4, 2009, while at 41.2 degrees north and 20.3 degrees west. Much like Karen, Grace formed as a small warm-core vortex within a much larger non-tropical storm system. As noted on X by Michael Ferragamo, NHC’s HURDAT 2 database also includes an unnamed tropical storm, similarly northeast of the Azores, whose first position, on September 8, 1952, was at 42.0°N, 23.0°W.

Non-tropical storm to hammer the mid-Atlantic this weekend

Though it’s not being tracked by the National Hurricane Center, a major autumn storm will be plaguing the U.S. Mid-Atlantic coast this weekend. Moderate to major coastal flooding could occur, and gale-force winds are possible—equivalent to a tropical storm—which could bring down some trees and power lines.

Jeff Masters contributed to this post.