'There is still more of hurricane season to go': Expert warns another tropical threat may make US landfall

The formation of Subtropical Depression Leslie and Tropical Rainstorm Kirk may only be the start of a busy next couple of weeks in the tropical Atlantic.

Sept. 10 marked the peak of the Atlantic hurricane season from a climatology standpoint. However, hurricane season does not officially end until Nov. 30. The coming weeks into mid-October often bring several additional tropical storms and hurricanes. This year may not be any exception.

AccuWeather long-range tropical meteorologists, led by Hurricane Expert Dan Kottlowski, projected two to four more tropical storms, of which one or two may become hurricanes, following Tropical Storm Joyce.

Two of those storms formed this past weekend in Kirk and Leslie, and a third area of concern may develop near the East Coast this week.

So far this hurricane season there have been 12 tropical storms, of which five became hurricanes. Three named systems - Alberto, Florence and Gordon - made landfall in the United States.

Thus far, Florence has been the only major hurricane (Category 3 or higher) in the basin.

AccuWeather originally predicted 12 to 15 tropical storms, six to eight hurricanes and three to four named-storm landfalls back on April 2. Due to a potential El Niño, the numbers were lowered slightly during mid-summer to 10 to 12 tropical storms and five to six hurricanes.

"There are several things we look at that include the current conditions, the status of El Niño and another cycle that tracks rising air over the tropics," Kottlowski said.

El Niño is the warm phase of tropical Pacific sea surface temperatures. When El Niño is going strong, air is rising and promoting a great deal of tropical activity over the Pacific. At the same time, westerly winds tend to blast from North America through much of the Atlantic basin. These strong winds tend to suppress tropical activity over the Gulf of Mexico, Caribbean and western part of the Atlantic Ocean.

"The anticipated El Niño for this upcoming fall and winter has been lagging, and we are still technically in a neutral phase," Kottlowski said.

"That's one reason why we saw the flurry of tropical storms and hurricanes in the past couple of weeks in both the Atlantic and the Pacific. The delay in El Niño was a caveat we mentioned during the initial hurricane forecast and a midsummer update."

Another parameter tracks a slow-moving wave of rising air, which can lead to storms that can develop tropically when over warm water and under the right conditions. It moves west to east around the equator. That parameter is known as the Madden-Jullian Oscillation, or MJO for short.

"The MJO is forecast to be in a phase that favors rising air over the Atlantic basin starting next week," Kottlowski said.

The rising air in the absence of disruptive winds may allow another flurry of tropical activity during the latter part of September into early October.

AccuWeather long-range meteorologists still believe that El Niño will ramp up this autumn.

"If El Niño does what our long-range team thinks, increasing westerly winds from North America will tend to break across the Atlantic and really shut down the hurricane season later in October and November," Kottlowski said.

"Even so, there is the chance for one more direct impact by a tropical storm or hurricane on the United States during the rest of the season," he said.

In the near term, there are a few features AccuWeather meteorologists are monitoring for potential impacts through the end of September.

"So, even though we are over the hump in terms of the average peak of hurricane season, there is still more of hurricane season to go," Kottlowski said.