Tropical disturbance in eastern Atlantic could be one to watch

Water vapor satellite imagery of tropical disturbance off the coast of Africa. (NOAA)

On Saturday, a wave of atmospheric energy moved west off the coast of Africa and entered the tropical Atlantic. This disturbance, which is being tracked as “Invest 94L” by the National Hurricane Center, could be an interesting area to watch for tropical cyclone development over the next week or two.

The National Hurricane Center is giving this area of interest a 30 percent chance of developing into a tropical cyclone over the next five days. The disturbance, which is known as an African easterly wave by forecasters, was showing signs of thunderstorm activity on Monday. The environment is modestly favorable for tropical cyclone formation, with warm sea surface temperature, moist air, and low wind shear.

Five day tropical weather outlook. This disturbance, located near Africa, is being given a 30 percent chance of tropical cyclone formation over the next fie days. (NHC)
Five day tropical weather outlook. This disturbance, located near Africa, is being given a 30 percent chance of tropical cyclone formation over the next fie days. (NHC)

Dry, Saharan air remains to the north of the disturbance, and while it is expected to move into drier air toward the end of the week, the wave could take advantage of its current moist environment and gain some strength. Sea surface temperature, which needs to remain warm to support hurricane development, is expected to remain sufficiently high, at least for the next couple of days.

Saharan air layer analysis. (University of Wisconsin-CIMSS/NOAA Hurricane Research Division)

Though none of the reliable weather models are forecasting tropical cyclone formation yet, the European and U.S. models are predicting that this disturbance could reach the Caribbean on Saturday. At that point, it remains unclear whether this potential storm will take a track that curves out into the Atlantic like Hurricane Bertha did, or if it will threaten the U.S. coast.

While it might seem like a slow hurricane season so far, 2014 is actually right on track to being average. There are typically only two to three tropical cyclones on the books for the year by August 1, and we’ve already seen three: Hurricane Arthur, which made landfall in North Carolina in early June, Tropical Depression Two, which fizzled out before reaching the Caribbean, and Hurricane Bertha, which tracked through the Caribbean and made landfall in Puerto Rico and the Dominican Republic before curving east to sea. Activity in the Atlantic usually picks up in August and September. By October 1, we will typically see around 9 tropical cyclones.

Average Atlantic tropical cyclone activity. (NOAA)

On Thursday, the National Oceanic and Atmospheric Administration forecast an increased likelihood that the Atlantic will see a below average hurricane season. NOAA is predicting a 70 percent chance that we will see seven to 12 named storms in 2014.

Angela Fritz is an atmospheric scientist and The Post's deputy weather editor.
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Angela Fritz · August 11, 2014