Dear Editor,
Typically, during the month of June in terms of climatological averages, we get one named storm; for the month of July, we get two named storms; by August 1, we tend to get three named storms as expected.
However, if we go by averages in terms of the climatology of the North Atlantic region, by mid-August several significant but notable changes occur over what we call the Main Development Region (MDR) which change things for the worse in terms of increased hurricane activity.
First, the sea surface temperatures (SST) become ideal where the threshold temperature for hurricane activity reaches and exceeds 26.5°C (80°F) for hurricanes to form, grow and thrive.
Imagine you put a cup of cold water in the microwave and heat it for four minutes. Up to the minute mark the water is just starting to heat up {June and July) and is too cold to enjoy or make the ideal cup of tea.
Well, there is going to come a point when that water will be “ideal” or warm enough to make that teabag start to change the color of the water and just warm enough that you can drink and enjoy a warm cup of tea all before the time gets to four minutes; like the three-minute mark.
Well August 15 is the “three-minute mark” or sometimes I would say “all hell can break loose then!”
The warm waters over the years have been unusually warmer than average in most cases in the MDR and elsewhere, and some people blame this on the impact of global warming or climate change.
That means the primary energy source and hence a very moist atmosphere (by a process we meteorologists call “latent heat of condensation”) of the tropical storm or hurricane is there to sustain the system and provide growth to the developing system.
Second, the Saharan dust, or what we as meteorologists refer to as SAL (Saharan Air Layer) typically inhibits the growth and development of these systems during the months of May, June, July, and early August (typically lasting to the second week of August) and significantly starts to tapper-off thereafter.
What the Saharan Air Layer does is rob the system of its moisture, an integral part of the tropical cyclone growth and development process and entrains dry air into the system preventing any future development of the system.
Therefore, whenever we have a Saharan Air Layer over us (which interestingly and coincidentally will be over us this week from Monday night to late Thursday of this week) it typically means hazy, hot, and dry conditions or rain-free conditions.
It, for the record, inhibits rainfall activities over our area but does not prevent them completely, I might add.
After about August 15, all hell typically tends to break lose over the North Atlantic because the Saharan Air Layer starts to significantly taper off, allowing unrestricted growth of the system.
Third, the winds in the upper atmosphere from mid-August to mid-September tend to become ideal and favor tropical cyclone development.
I will try and explain this as simply as possible. Imagine you are trying to get smoke from a chimney top to rise from the ground to the upper layer of the atmosphere, or let us say to the moon for ease of reference.
Now on a calm day, that smoke will get its best chance to reach the upper atmosphere or the moon (in the case of a hurricane, a Cat 5 storm) because there are no impediments or winds to inhibit its progress.
On the other hand, on a very windy day, the chance of that smoke getting to the moon, or the upper atmosphere, is severely restricted due to the strong winds blowing the smoke particles away from rising to their intended location.
So, in plain language, the smoke will not get to the moon or upper-level of the atmosphere because of the strong winds or be delayed or become less windy on a given day at a given time – ta da!
You have just learned what my met teacher took two weeks to explain to me in my first year of met school!
The term we meteorologists use is “wind shear”; so just imagine the strong winds at different levels blowing the smoke, they are the wind shear (tearing the system apart is what you typically hear the meteorologists say on TV or radio), so in layman’s term, the winds are very strong and blowing the smoke particles apart from getting to the moon.
It’s intended destination, which in our case is a Cat 5 hurricane, or you might hear “atmospheric conditions are not conducive for development”, meaning Saharan dust, colder waters, wind shear, etc. are impeding development.
Fourth, there are about four major areas where hurricanes typically develop, and from mid-August to mid-September, most of those areas become a hive of activity.
In fact, the climatological averages jump from three to about nine named storms by September 16.
All four areas tend to have some form of activity during this period.
The most active of them would be the Cape Verde type hurricane, which comes off the African Coast and moves through the Atlantic Ocean, gaining strength before contacting the Eastern Caribbean islands anywhere from a tropical storm to a Cat 5 hurricane, and if the path and weather systems align, one could pass over our islands.
Fifth, for a hurricane or tropical storm to form, it needs a pre-existing disturbance to form from. In other words, hurricanes do not just simply develop out of the clear blue but need an initiating factor.
That can be anything from an old frontal boundary, an upper-level trough or low pressure, a surface low-pressure system, or a tropical or easterly wave.
For the Cape Verde type hurricanes (which account for about 85 percent of the hurricane activities in the North Atlantic) it is the tropical or easterly waves that provide the initiating factor, and they do not become more frequent during this time, but the atmosphere becomes more unstable, meaning more of them become more active and develop.
In other words, these waves become more conducive to developing into a tropical depression, tropical storm, or hurricane.
— Wayne Neely