A day after lashing Puerto Rico with flooding rains and winds gusting over 40 miles per hour, Karen is continuing its trek northward. Still a tropical storm, Karen is expected to maintain strength or slowly strengthen, eventually stalling and possibly making a turn west. That makes Karen one to watch for residents in the Bahamas and southeast United States, where Karen’s long-anticipated tour of the west central Atlantic might bring it uncomfortably close.

Karen is a capricious storm. Less than 36 hours after being classified as a tropical storm Sunday morning, Karen weakened into a tropical depression, sparking doubts that the system would ever make it to Puerto Rico intact. Barely a day later, Karen intensified into a tropical storm once again as it drew near the island territory. The main impacts in Puerto Rico and the Virgin Islands weren’t from wind, however; the headaches stemmed from rain.

Just southwest of San Juan, 3.46 inches of rain fell, with 3.50 inches in Utuado along the island’s western half. A number of flash flood warnings were issued in the island’s mountainous terrain. Doppler radar indicates as much as half a foot fell in Juana Diaz and Villalba municipalities. It’s estimated that more than 14 inches fell just offshore.

Karen is sitting about 150 miles north-northeast of San Juan, with maximum central winds of 45 mph. Over the next day or two, the system will casually strut northward or slightly north-northeastward, as if heading out to sea. But then the storm slams on the brakes and throws it in park. Karen could stall over the open Atlantic for 12 to 24 hours from late Thursday into the latter half of Friday.

A group of simulations from American (blue) and European (red) computer models from Wednesday morning for Tropical Storm Karen. Each color strand represents a different model simulation with slightly altered input data. The strands are clustered together where the forecast track is most confident but diverge where the course of the storm is less certain. The bold red line is the average of all of the European model simulations, while the bold blue one is the average of all the American model simulations. (StormVistaWxModels.com)

Overnight, Karen exhibited a burst of “convection,” a cluster of shower and thunderstorm activity blossoming near the system’s loosely defined center of circulation. Cloud tops warmed slightly, and thunderstorms weakened a tad Tuesday morning, with additional fluctuations in strength possible over the next 24 to 48 hours.

A burst of convection fired up overnight, with cool cloud tops indicating robust upward movement. Karen took a breather Tuesday morning but may resume intense thunderstorm activity shortly. (TropicalTidbits.com)

What’s next on Karen’s agenda? It’s not clear. Karen may start to make a bizarre clockwise loop Friday, making a full 360 degrees, turning around aimlessly. Karen’s northward progress will be stunted by the Bermuda High — a big atmospheric roadblock in Karen’s path — which is likely to force the system west.

The National Hurricane Center’s forecast favors an acceleration toward the west into this weekend, with Karen setting its sights on the Bahamas. While track forecasts at this time feature considerable uncertainty — the average error in track five days out is 189 miles — it’s a trend that should have folks in the Bahamas and perhaps Florida carefully monitoring Karen’s progress.

Forecasting Karen’s strength is a challenge, as well. Will the system become unpredictably feisty or remain innocuous into the weekend?

Models are split down the middle, with the vast majority showing either a continuation at tropical storm strength or even a gradual decline back to depression status over the next five to seven days. That’s because those models depict a scenario in which Karen’s lower-, middle- and upper-level circulations “decouple,” becoming misaligned. That would give rise to a weakening trend, as in that case Karen’s central vortex would be disorganized and its updraft air flow interrupted.

But, alternatively, Karen might become more formidable. Following the 270-degree turn, Karen will find itself over very warm ocean water — sea-surface temperatures around 84 degrees mean the lower atmosphere is replete with fuel. At the same time, relaxed flow at the upper levels means large quantities of hostile wind shear — a change of wind speed with height — will not be present. That means Karen’s central vortex could remain intact, allowing the fickle system to take advantage of the plentiful oceanic fuel over which it traverses. According to the National Hurricane Center, that “favors strengthening.”

Tropical storm Karen continues to trek north after lashing the island of Puerto Rico with breezy winds and heavy rainfall. (NOAA/RAMMB)

For the time being, Karen is expected to slowly inch its way up toward the 65 or 70 mph mark by the start of next week. However, there’s not much holding Karen back from becoming a more serious storm if things line up right. Assuming Karen makes the loop-de-loop and starts heading west, it may flirt with hurricane strength late this weekend.

In the longer term, anything is on the table, but a continued westward track toward the Southeast next week cannot be ruled out. The European modeling system, in particular, has consistently presented this as a possible scenario.