By Alex Sosnowski, Expert Senior Meteorologist
September 13,2013; 9:39PM,EDT
Conditions have been limiting the intensity of tropical systems in the Atlantic basin so far this season, but the season is far from over.
Humberto was the first hurricane of the season, but it will not be the last.
On average, by the middle of September three hurricanes have formed.
According to Hurricane Expert Dan Kottlowski, "A large area of high pressure over the central Atlantic has been very strong and very good at driving dry air southward into the tropics into September."
Generally it is easier for tropical storms to form and tropical storms to strengthen into hurricanes when there is an unobstructed supply of moisture available.
"There have also been frequent surges of wind shear [disruptive winds at mid-levels of the atmosphere] present just about every time we have had a system begin to develop," Kottlowski said.
Winds of this sort not only tend to disrupt the circulation around the developing system, but they can also literally shear off the top of the system or cause it to be very lop-sided.
While the number of hurricanes is running behind the average pace, the Atlantic is churning out an above-average number of tropical storms.
By the middle of September, the average number of tropical storms is six. So far this season, there have been eight, with a ninth system already in the works over the southwestern Gulf of Mexico.
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While the perception of the season thus far by the public and some of the media is that the season is a dud in terms of intensity and direct impact to land, it is far from over.
More than a dozen lives have been lost already this season from Tropical Storm Fernand.
The hurricanes have gotten a late start this season. In fact, so much of a late start that a satellite era record for the latest first hurricane came to within several hours of being broken. The old latest first hurricane record was Gustav, which became a hurricane shortly after 8:00 a.m. EDT on Sept. 11, 2002.
Humberto, which has already maxed out at Category 1 status with 85-mph winds, was upgraded to a hurricane at 5:00 a.m. EDT on Sept. 11, 2013.
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So far, Tropical Storm Andrea during early June was the only system that has made landfall in the U.S.
Predicting the intensity of existing and yet-to-develop tropical systems is the most challenging. There are many variables in the short term and long term that are of influence.
One of the most basic players in predicting intensity that can make or break a budding tropical system is the interaction with large land areas or mountainous islands and pockets of warm, versus cool, water.
When a seasonal forecast is made, the track of individual hurricanes or tropical storms before they form is not known. Judgement calls are made comparing the average numbers of hurricanes with the expected weather pattern for that season.
We cannot say with a high degree of certainty that a total of three tropical systems will make landfall in the United States, but rather that based on the pattern moving forward there could still be a slightly above-average number of landfalls by a tropical storm or hurricane in the United States.
"The ingredients have been and are still there this season, but thus far the tropical atmosphere has been out of sync for hurricane development," Kottlowski said, "In order for there to be a large number of hurricanes and multiple major hurricanes, the atmosphere has to be running like a fine-tuned engine."
The Atlantic has sprung to life of late with three organized tropical systems active at the same time during Thursday: Hurricane Humberto, Tropical Storm Gabrielle and Tropical Storm Ingrid.
On average, there have been twice as many hurricanes during the three months of September, October and November, compared to June, July and August.
"We still expect additional hurricanes to form in the Atlantic this season and odds are a couple of these will become major hurricanes," Kottlowski said.
Meteorologists and the public still have a great deal more watching to do this season and hoping that if and when hurricanes come calling they avoid populated areas.
It takes only one hurricane, tropical storm or hybrid storm to have a major impact on a populated area and define a disastrous season. Agnes, Andrew, Diane, Hazel, Katrina and Sandy were a few such storms that made a lasting mark on their seasons and changed lives forever.
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