Atlantic hurricane season activity could pick up into September


Despite almost unanimous predictions of above-average activity, it’s been an ominously quiet start to the hurricane season — though that could change in the coming weeks.

There has not been a named storm in the Atlantic basin since Colin, a tiny vortex of gusty showers that clawed along the Carolina coast on July 3 with minimal impact. It’s been quiet since then, despite the calendar approaching September when the hurricane season historically peaks in activity.

There are signs that a trend reversal is imminent after a quiet week in the last few days of August. The National Hurricane Center has outlined a system to watch, noting that a sudden surge in activity is possible. It’s far from a guarantee, but it also stands to reason that tropical sleep can’t last forever.

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The historical peak of the hurricane season is around September 15, but mostly from late August to mid-October ranks as the busiest stretch of the week when it comes to tracking the tropics. There are an average of 14 named storms in any given season, seven of which could be hurricanes, but NOAA forecasters have continued to repeat previous calls of 14 to 20 named storms, six to 10 hurricanes, and three to five major hurricanes.

Even the quietest seasons have produced meteorological monstrosities.

For example, there were only seven named storms in 1992, but the first was Category 5 Hurricane Andrew, which besieged southern Florida and hit the National Hurricane Center headquarters with a 163-mph gust. Conversely, when storms spent their lives over the open ocean, the potentially busier seasons on paper had comparatively less impact on humans.

But when it comes to tropical storms and hurricanes, it only takes one.

Tropical disturbance in the Caribbean

On Wednesday morning, the National Hurricane Center monitored a disturbance near the coast of northern Honduras. Most of the bad weather, including some robust thunderstorm activity, was north of the mainland and over the western Caribbean.

The system is currently crooked, but it showed signs of healthy runoff or exhaust at its upper levels. Tropical storms and hurricanes breathe, so to speak, and the more they breathe upwards, the more warm, moist air they can draw in near the surface to fuel their continued growth and maturation.

Minimal organization of this disturbance is likely by Thursday, but it will slide into Campeche Bay by Friday. There it will encounter very warm sea surface temperatures – supporting strengthening – but wind shear is moderate. Wind shear, or a change in wind speed and/or direction with altitude, has been known to play a tug-of-war with tropical cyclones. Strong wind shear can stunt a storm’s vertical development and often unbalance storms.

It’s impossible to be sure what will happen to the system in more than three or four days, but by and large it will likely drift northwest, either toward northern Mexico near Tamaulipas or far south Texas . Local heavy rainfall is possible if left intact, but any forecast beyond that is pure speculation.

The National Hurricane Center estimates a 20 percent chance of a well-formed tropical cyclone developing, but it’s still worth monitoring.

Across the Atlantic, there are signs that activity could pick up more significantly over the next 10 days.

Weather models focus on more aggressive tropical waves rolling off the coast of Africa and spreading west through the MDR or Main Development Region. Sometimes called “Hurricane Alley,” the MDR is the belt of the tropical Atlantic that can occasionally produce long-lived, powerful storms back-to-back.

It’s far too early to diagnose simulated waves as a potential storm, but several other flow factors could be supporting storm formation. Wind shear seems likely to be taking a breather, which could allow for better vertical development of a storm. Dust from the Sahara could also prevent storm formation, but the layer of hot, dry air in the middle layers of the atmosphere in which it is embedded should thin out over time. That could allow some tropical systems to thrive, especially if the oceans continue to warm.

The Gulf of Mexico could also become increasingly favorable for potential storms towards the end of the month; The Gulf is about half a degree to a degree above average in terms of sea surface temperature.

Simply put, August came in like a lamb — but his exit might not be so gentle.

About Mike Crayton

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