A tropical storm warning has been issued for Puerto Rico, including Vieques and Culebra, as well as the U.S. Virgin Islands, with Tropical Storm Karen a day away from passing near or directly over Puerto Rico. Heavy rain and gusty winds are most likely on the island Tuesday.

The system is about 150 miles west of Martinique, north of Venezuela. But where Karen’s center is, it’s not even raining ― the bulk of shower and thunderstorm activity remains well south of the center of circulation.

The National Hurricane Center expects that “disorganized Karen continues to move slowly,” describing Karen as “disheveled.” In fact, there is even some forecaster doubt that Karen has winds reaching the 39 mph threshold for designation as a tropical storm.

The system has been struggling to blossom beneath hostile upper-level winds, which have been working to disrupt Karen’s circulation in an attempt to tear it apart.


Karen's center remains largely exposed, indicating the thunderstorm tops are most prevalent south of the center. However, a new batch was bubbling up just northeast of the center Monday morning. (TropicalTidbits.com/National Oceanic and Atmospheric Administration)

Karen looks to continue northward at current strength, with “fluctuations” likely over the next 48 hours. While Karen may make an attempt at consolidating some as it slips into a pocket of slightly less vicious upper-level winds, its time to do so is limited. Karen is expected to pass near or over eastern Puerto Rico on Tuesday afternoon. The National Hurricane Center is calling for it to have 40 mph winds at that point, with lesser gusts as one heads farther away from the center of circulation.

Puerto Rico’s electrical infrastructure is still particularly vulnerable in the wake of Maria, with any unwelcome wind-driven shake-ups enough to spell trouble. The wind threat should remain relatively low, but it wouldn’t take much to realize greater impacts.

Of greater significance is the potential for locally heavy rainfall, particularly over the eastern half of the island. Rainfall totals are forecast to range between 2 and 4 inches, but a few isolated locales could pick up 6-inch totals, especially if Karen jaunts west of the current forecast track. This risk includes the San Juan metro area. Any heavy rainfall can be problematic in the mountainous terrain of Puerto Rico, for which reason there is the potential for isolated flash flooding. Conversely, if Karen shifts farther east, the flooding risk will be more limited.

What does Karen do after that? Karen’s future depends on whether its mid-level vortex survives the trip past Puerto Rico. The mountains could shear it apart. But if Karen shoots the gap between Puerto Rico and the U.S. Virgin Islands, its axis of spin will remain largely intact. That scenario would make it one to watch in the Bahamas and, possibly, the southeast United States and Gulf of Mexico.


A group of simulations from American (blue) and European (red) computer models from Monday morning for Tropical Storm Karen. Each color strand represents a different model simulation with slightly altered input data. Note that 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)

The reason? Steering currents on the south side of the Bermuda High, the large clockwise circulation frequently present in the western Atlantic subtropics, could help Karen make a hard left turn once it moves north of Puerto Rico if it’s still intact. After Tropical Storm Jerry pulls away, a lobe of the Bermuda High will be displaced southwestward, essentially blocking Karen and shunting it northwest toward the southeast United States or perhaps west toward Florida and the Gulf of Mexico.

The atmosphere will be more supportive of development during that time, as well. It’s simply too early to know how realistic a scenario this is, but we’ll have a much better idea by the middle of this week.

Meanwhile, Tropical Storm Jerry’s out there doing its thing. It has 65 mph winds as it spins 400 miles south-southwest of Bermuda. It will weaken slightly as it passes just northwest of Bermuda on Wednesday, its track almost identical to that of Humberto last week. A tropical storm warning is up for the island, and conditions could begin to deteriorate there Tuesday night.


A stunning satellite shot of Jerry on Monday morning. With weakening or unhealthy storms, it's possible that the heaviest shower/thunderstorm activity is removed from the center of circulation. That's why we can see the low-level cloud field so well. (TropicalTidbits.com/NOAA) (TropicalTidbits.com/National Oceanic and Atmospheric Administration)

Our attention then turns to a system just off the coast of Africa, which is “expected to become a tropical storm later today,” according to the Hurricane Center. The name Lorenzo is up next. The system is expected to get its act together quickly, intensifying to hurricane strength by midweek. In fact, soon-to-be Lorenzo could be a major hurricane by the end of the workweek. But it’s anticipated to remain largely out at sea.


The system that will soon become Lorenzo could approach major hurricane status by the end of the week but should remain largely out to sea. (National Oceanic and Atmospheric Administration/National Hurricane Center)

After that, it looks as though we’ll have a break for a few days before the next notable African Easterly Waves roll off the African coast at the start of October.