The National Hurricane Center estimates that one of the waves has about a 50/50 shot of developing into a tropical depression or named storm in the coming five days, while the other was assigned a 70-percent chance. Both disturbances are in positions that, if they strengthen, could result in eventual impacts to land.
If one or both of these systems earn names, the next two on the list of storms are: Laura and Marco.
The forthcoming bout of activity has been anticipated for weeks because of the incipient overlap of several key weather systems that will enhance rising motion over the Atlantic. That will foster hurricane development and make tropical cyclones more likely.
Tropical wave 1
The first disturbance of the pair has already trekked across the ocean, soon to arrive in the Windward Islands as it nears the Lesser Antilles. Dubbed “Invest 97L,” the system had plenty of deep convection — or shower and thunderstorm activity — associated with it Monday. But it lacked any sort of rotation or organization about a center, which limits for now its prospects of strengthening.
Part of the reason for this unimpressive structure was the system’s forward speed of nearly 20 mph. When a disorganized system moves too quickly, it can, in a sense, outrun itself, and its thunderstorms don’t have the opportunity to build.
Invest 97L looks to bring gusty winds, squally weather and locally heavy rainfall to the Windward Islands on Monday and early Tuesday. A few rainfall amounts of up to three or four inches are possible, and a flash flood warning is in effect. A few parts of the island saw up to an inch of rain overnight Sunday into Monday morning, according to the Barbados Meteorological Services.
By late this week, the system could be rolling through the western Caribbean, at which point it is expected to slow down, thanks to relaxed upper-level winds. That could prove more conducive to development between Thursday and Saturday, although confidence remains very low.
Computer model simulations have shown mixed signals as to the potential persistence of the wave. Regardless, any area of spin in the Caribbean always bears watching.
Tropical wave 2
The second system is perhaps more interesting in the short term, with acutely greater probabilities of development. That one was located south-southwest of the Cabo Verde Islands offshore of Africa on Monday morning, and it was unimpressive to look at for the time being. A change of wind speed and/or direction with height, known as wind shear, was hindering its ability to organize.
On the other hand, the system has managed to outmaneuver the Saharan Air Layer, or SAL, whose mid-level warm, dry air can suppress tropical cyclone development. That is one fewer obstacle that the system, known as Invest 97W, will need to overcome.
In the days ahead, Invest 97W is slated to drift westward at a decent clip and could begin to encounter a more favorable atmospheric environment later in the week as it approaches the Lesser Antilles. With a bearing a bit north of due west, it appears the Leeward Islands will be up for heavier rain and wind gusts with this one, regardless of potential development.
In the longer range, it’s impossible to predict the strength of a system that hasn’t formed and whose track is highly uncertain. However, the Bermuda High — a large sprawling dome of high pressure over the central North Atlantic that acts as a guard rail for hurricanes — probably will repress Invest 97L’s northward movement or ability to recurve. That could, in turn, make it something to watch as it eventually heads more west-northwest toward the Bahamas or Southeast very late in the week.
An active period to continue
The 2020 Atlantic hurricane season has been a record busy one, with 11 storms forming. That’s an average season’s worth of cyclones. Among the storms have been the earliest C, E, F, G, H, I, J and K storms on record.
None has been particularly impressive categorically, and most systems have been relatively short-lived. That is likely to change though as we head into the heart of the Atlantic hurricane season.
Part of the reason for the enhancement in activity? A convectively coupled Kelvin wave. It’s certainly a mouthful, but the underlying concept is simple: It’s a large, overturning circulation in the atmosphere with rising air on one side and sinking air on the other.
Where the air sinks, hurricane chances are less. But where the air rises, an enhancement in tropical cyclone activity is likely.
That wave is scheduled to team up with a similar feature that will enhance storminess known as the Madden-Julian Oscillation, or MJO. Together, they will work to kindle any fledgling attempts at tropical cyclone development over the Atlantic in the coming weeks.
Meanwhile, anomalously warm waters over virtually the entire Atlantic basin, the result large part of human-induced climate change, will amplify the threat of a higher-end storm. Warmer waters increase the potential strength of hurricanes and the amount of rain they can produce.
Warm ocean waters also can boost the odds of rapid intensification, which can be especially problematic in the hours preceding a hurricane’s landfall. Meteorologists still struggle to adequately predict rapid intensification in advance.
The period of heightened activity, which could at times feature multiple hurricanes simultaneously across the Atlantic, is set to last several weeks and could bring us to the climatological peak of hurricane season in mid-September.