No hurricanes have been active in the Atlantic Basin since July 12 despite August being the second-most-active month for Atlantic hurricanes, but some forecast guidance suggests the tropical Atlantic could wake up over the next two weeks.
Multiple tropical waves are forecast to emerge off the coast of western Africa, potentially spinning up into tropical cyclones as they track westward across the tropical Atlantic Ocean, known as the Main Development Region (MDR) for Atlantic hurricanes.
The National Hurricane Center said on Tuesday that one such tropical wave moving off the African coast by Thursday bears watching for some development in the eastern Atlantic over the weekend.
We’ll also be monitoring other tropical waves for signs of life as they spread westward from the Atlantic to the Caribbean and Gulf of Mexico.
Often referred to as African easterly waves, tropical waves are batches of energy and general spin in the atmosphere that develop due to temperature contrasts in northern Africa.
“Medium-range models are indicating an uptick in activity over the Atlantic’s Main Development Region in the coming 10 to 15-plus days,” said Dr. Michael Ventrice, a meteorological scientist at The Weather Company, an IBM Business.
“Many forecasters are seeing numerous strong low-pressure systems, associated with the model’s prediction of an uptick in African easterly waves pushing off western Africa, across the MDR towards the end of the European model’s ensemble runs.”
One of the reasons for this potential uptick in activity is that the Madden-Julian Oscillation (MJO) is expected to enter its active phase over the Atlantic Ocean and Africa regions, which often corresponds with an uptick in tropical cyclone activity across the Atlantic Basin’s MDR, Ventrice added.
Since this forecast is in the extended range, there is still uncertainty when it comes to computer model guidance, he cautioned.
“I think we are going to see some activity in the coming two weeks across the MDR, but there’s a chance the models are not handling the tropics correctly and things end up less active than what is being touted,” Ventrice said.
For now, it is too early for any specifics, but it’s a reminder we are in the peak of the hurricane season. Residents of coastal locations should have a hurricane preparedness plan in place every year no matter how active or inactive of a season is expected.
September is the Peak Month for Atlantic Hurricanes
Historically speaking, September has recorded the most Atlantic hurricane formations since 1851 with 404. That’s an average of two or three forming in the month every year, according to National Oceanic and Atmospheric Administration (NOAA). August ranks second with 245 hurricanes, and October ranks third with 205.
The period between Aug. 20 and Oct. 10 accounts for 60 percent of all Atlantic Basin hurricanes and 75 per cent of all major hurricanes (Category 3 or stronger) in that basin, according to Dr Phil Klotzbach, a tropical scientist at Colorado State University.
Atmospheric conditions are more favorable over a much larger expanse of the Atlantic Basin during the peak months of August through October than early or late in the season.
In June, the tropical cyclone formation zones are confined to the Gulf of Mexico, western Caribbean Sea or just off the southeastern U.S. coast. This is one reason for the relative lack of early-season hurricanes compared to August through October. Storms that form in these areas early in the season don’t have far to go before reaching land.
From July into August and September, the formation zone gradually spreads eastward until the so-called MDR, from the Lesser Antilles to just off Africa, is in play. This opens up the potential for Cape Verde hurricanes to make the more-than-3,500-mile trek from the eastern Atlantic Ocean toward the Caribbean islands or U.S. coast.
One factor that may influence this year’s peak hurricane season is the Atlantic Multidecadal Oscillation (AMO), which is a long period of upward and downward swings in tropical activity in the Atlantic Basin.
The AMO is trending negative this season after being predominantly in its positive phase since the mid-1990s. Each phase lasts 20 to 40 years and is a result of changes in the system of oceanic currents in the northern Atlantic Ocean.
This oscillation is the climate background that all other climate and weather patterns build on in the Atlantic, including El Niño.
Research has shown that negative AMO Atlantic hurricane seasons can have a slightly later than normal peak, according to a tweet by Eric Webb, a University of North Carolina at Charlotte graduate student.
Some computer model guidance is suggesting that may be true this year, with an uptick in tropical activity in late September, beyond the typical Sept. 10 peak of the hurricane season.
Last September was the most active month on record for Atlantic hurricanes following Category 5 hurricanes Irma and Maria and Category 4 Hurricane Jose.