Atlantic basin showing signs of life as development chance arises
AccuWeather meteorologists are closely monitoring a batch of showers and thunderstorms moving over the Atlantic Ocean just west of Africa that has some potential to evolve into a tropical depression or storm in the coming days. Though development is far from certain, it is the first glimmer of activity throughout the basin after a more than month-long lull.
A tropical disturbance, or a tropical wave, designated Invest 97L by the National Hurricane Center (NHC), emerged near the northwestern coast of Africa over the weekend as a candidate for development during the second half of this week to this weekend. As of early Tuesday, the wave was in what meteorologists describe as a "garden spot," an atmospheric pocket that is surrounded by conditions considered too hostile for tropical storm formation.
This image of the tropical Atlantic was taken on Tuesday, Aug. 9, 2022. Of all the tropical waves (dashed lines) the one that is most likely to develop later this week was located just west the coast of Africa (right).
"The tropical wave is far enough away from the 'river of shear' to the north and just south of the dry, stable air," AccuWeather Hurricane Expert Dan Kottlowski said, referring to the nearby conditions in the atmosphere that are inhibiting development. The "river of shear" Kottlowski described is a reference to wind shear, an area of strong, high-level winds that can often prevent tropical development or can cause an established tropical system to weaken.
"If this wave moves due west for the next few days and stays south of the shear zone, then it has a chance of becoming a depression and tropical storm," Kottlowski said. A medium chance of development was originally assigned to the tropical feature on Monday, but the potential has been rolled back as of Tuesday as dry air surrounding the system may already be taking its toll.
To have three tropical storms so early in the season was well ahead of the average pace. But with August now well underway, the same number of storms thus far has the season at about average pacing. Typically, the first hurricane forms around Aug. 11, and this season is very likely to fall short of that mark, even if a tropical storm takes shape. The last hurricane in the Atlantic basin was Sam, which roared over the middle of the ocean from late September to early October in 2021.
At the start of the week, the shear zone stretched across much of the Caribbean and into the central Atlantic. It is possible that the shear zone will remain or change very little through next week. Little change in the wind shear over that area could limit development beyond several days and, perhaps, could cause the system to weaken, should it develop in the near term.
As this feature gradually turns northwestward late this week and over the weekend, it will run into that river of shear, Kottlowski explained. "As a result, this potential developing tropical system is likely to be short-lived once it starts to gain latitude."
Most weak tropical systems tend to be guided along by breezes that flow clockwise around a large area of high pressure, known as the Bermuda high, that hangs out over the central Atlantic.
The organization and strength of the system could very well influence how far west the system will travel before making a turn to the northwest. A strong and well-organized tropical storm is more likely to turn to the northwest sooner, compared to a weak system, such as a tropical depression, that might continue farther to the west before tracking to the north.
From late in the weekend to early next week, the most likely scenario is for the system to turn northwestward soon enough to keep the bulk of the thunderstorms and gusty winds northeast of the Lesser Antilles. However, a weak system could track close enough to drag showers and thunderstorms across some of the islands in the eastern Caribbean.
And this may be the basin's only chance for a named storm until the second half of the month.
"Outside of this particular tropical wave, not much else stands out as far as candidates for development through Aug. 20," Kottlowski said. But, AccuWeather meteorologists will continue to monitor additional tropical waves moving westward from Africa. There will likely be a non-tropical storm that forms along a cool front near the Carolina coast this weekend.
While this storm is forecast to move out to sea next week, it could take on tropical characteristics over time.
It is not uncommon for the Atlantic basin to go for an extended period without any named storms during the middle of the summer. This is the time of the year when there is a handoff from near-land development in the western Caribbean and the southeastern Atlantic coast to the main force of tropical development more than 1,000 miles farther to the east. A gap in development often occurs during the handoff, since vast areas of wind shear are accompanied by inhibiting dry air and dust over much of the central Atlantic.
The heart of Atlantic hurricane season is ahead. Many of the storms that evolve into tropical storms and hurricanes from mid-August to early October originate from tropical waves that move westward from Africa. As wind shear, dry air and dust become less extensive during the late summer and early autumn, the tropical waves take center stage and find conditions that are much more supportive of development.
AccuWeather meteorologists still expect a bumper crop of tropical storms and about an average number of hurricanes. In terms of direct impacts on the U.S., including Puerto Rico and the Virginia Islands, an above-average number of storms is likely.
One of the reasons for the lack of tropical activity in recent weeks is that "there has been more than an average amount of sinking, stable air over the Atlantic basin thus far this season," Kottlowski said.
Sinking air is another factor that often prohibits the atmosphere from forming the towering clouds and thunderstorms that can be a precursor to a tropical depression. If this sinking air persists over a broad area into part of the main hurricane season, then it could result in lower numbers of tropical storms and hurricanes in the end.
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