That seems likely to change in short order with the development of a new cluster of storminess and downpours a few hundred miles west-southwest of the Cabo Verde islands. Unlike its predecessors, this one’s westward track could bring it precariously close to land before it begins curving northward around sprawling high pressure.
Models differ in their simulations of the storm, with some depicting it as heading out to sea while others bring it close to the Leeward Islands and Lesser Antilles. All are bullish in their projections of the nascent storm’s intensity, which could become a hurricane by early next week.
In the nearer term, parts of the eastern Lower 48 are actually dealing with some tropical trouble in a rather roundabout way. The long-since-dead remnants of Hurricane Nicholas, which made landfall southwest of Galveston as a Category 1 hurricane on Sept. 14, have lingered over parts of the Deep South for more than a week. That left behind a blob of tropical moisture that’s being squeezed north ahead of a cold front, setting the stage for torrential downpours and pockets of flooding on the East Coast.
The tropical disturbance now
As of 8 a.m. Wednesday, the tropical disturbance that will eventually become Sam was an “invest,” or a region of activity that the National Hurricane Center was closely monitoring. It estimates the system has a 90 percent chance of developing within the next 48 hours.
On satellite imagery, it’s clear that Invest 98L is on the verge of becoming a tropical depression, or the precursor to a named tropical storm. Healthy outflow was visible northwest of the center, as shown by tendril-like strips of cloud cover pointing away from the storm’s “central dense overcast” region. Outflow is a term given to high-altitude exhaust exiting a storm. More efficient outflow processes make it easier for a storm to draw in more warm, humid air near the surface and intensify.
Invest 98L is also roiling with convection, or shower and thunderstorm activity. The system’s rotation is obvious on satellite images, but it’s important to remember that the satellite, GOES-East, is peering down from 22,000 miles above the Earth. Because we can’t see what’s happening at ground level, it’s impossible to ascertain whether that circulation extends down to the surface. That’s why, when a system gets closer to land or appears more threatening, it’s often investigated by hurricane hunter aircraft.
Invest 98L will probably become Sam within a day or two. It’s moving over tropical waters supportive of intensification, and wind shear — a change of wind speed or direction with height in the atmosphere — is weak. That will allow its vertical structure to develop without being knocked off-kilter.
Then Sam will continue west around high pressure banked over the Azores. The wild card is how strong and large that high pressure is. A stronger high would continue to suppress Sam south and drive it west, dangerously close to the Lesser Antilles.
Sam’s future track is also predicated on its strength. A stronger storm system would be taller and “feel” more mid- to upper-level winds. That would drag it north and out to sea. A weaker system initially would make it farther west before intensifying.
While nothing is imminent or guaranteed, it’s a good idea for those in Puerto Rico and the Leeward Islands to monitor the progress of the system.
Other systems to watch
There are several other tropical systems to mention, but they are merely fish storms over the open ocean. Both Peter and Rose were tropical storms but are now tropical depressions whirling to their demise over the central Atlantic.
The remnants of Nicholas are juicing up the atmosphere in the Eastern United States, bolstering the risk of heavy downpours and flash flooding. Parts of the Appalachians are expecting up to half a foot of rain.
In the North Atlantic, the remnants of Tropical Storm Odette, which spent a short life breezing south of the Canadian Maritimes late last week, could generate some new thunderstorm activity over warmer waters near the Gulf Stream. There’s a roughly 50-50 shot it could regain classification and be designated subtropical.