The past couple of weeks we have really seen the Atlantic hurricane season really start to ramp up. As a matter of fact, we are approaching the peak of hurricane season which historically has peaked September 10th.
So now that we know that this is the time of year where we see the most tropical activity, lets learn about the “What’s, the Why’s, the Where’s, and the How’s” tropical systems develop.
To begin, lets dive into the birth of a tropical system.
In the above photo that is the most recent as of today shows an Infrared Satellite view of the West African coast. Along with it is what has developed into Tropical Storm Gaston and another energy wave moving into the East Atlantic.
So what is it that you’re looking at? It looks pretty, full of color, but what is it actually?
To answer this, you have to think about weather systems back here at home. For example, a cold front gets its energy from the contrasts between two air masses. In the United States, cold Canadian Arctic Air contrasts with the warm Gulf of Mexico Air. This is essentially the reason behind showers and thunderstorms tend to develop in front of cold fronts. Its the contrast between two different air masses. (Now I can go into the dynamics, but that is not why I am writing this article.) Back to Africa, the same idea is at work over the Saharan desert, hot air mass over the Saharan contrasts with the cool and humid air mass from Central Africa create the same “Cold Front” affect, pushing waves of energy into the East Atlantic.
This happens more frequently from July-October because during these months the Saharan desert heats up the most, thus creating a bigger contrast.
The biggest question we have been getting has been why do they call it “Invest XX”. Great question, and it has a simple answer. Shown above is the current satellite loop of Invest 99L. NOAA, or the National Oceanic and Atmospheric Administration oversees the National Weather Service and in this case the National Hurricane Center. When the team of meteorologists at the National Hurricane Center see a wave of energy move into the Atlantic that shows potential to develop into a tropical system, they label it Invest, which is short for Investigation. This means they focus resources on carefully monitor the collection of showers and thunderstorms for signs of development. This is why you have heard of the Hurricane Hunter airplanes. These are specially designed aircraft from the US Air Force or NOAA whose mission is to fly into the system and monitor all the parameters.
After monitoring a promising system there are certain criteria NOAA looks at to give an Invest and upgrade to a named storm. The first and most important aspect for a system of energy to be classified as a tropical cyclone is when the system organizes itself from an area of thunderstorms and showers into a non frontal (this means it is not a product of a cold front/warm front etc) cyclone. We look at areas of deep convection, much like a thunderstorm here, however these are very much organized. We also look for winds at the surface moving in a closed circular motion which creates a well defined center. This is what we call the Eye Wall, more on that later.
Once there is a defined center of circulation and the system becomes organized the Invest now receives a name. From a Tropical Depression to Tropical Storm and finally to a Hurricane, the levels of strength is measured by sustained surface wind speeds. This means the speed of the winds for a period of 1 minute. Here is this list of the levels of strength the system needs to reach each category;
Tropical Depression – maximum sustained surface winds at 38mph or less.
Tropical Storm – maximum sustained surface winds at 39mph to 73mph.
Hurricane
Category 1 – maximum sustained surface winds at 74mph to 95mph.
“Very dangerous winds will cause some damage”
Category 2 – maximum sustained surface winds at 96mph to 110mph.
“Extremely dangerous winds will cause extensive damage”
Category 3 – maximum sustained surface winds at 111mph to 129mph.
“Devastating damage will occur”
Category 4 – maximum sustained surface winds at 130mph to 156mph.
“Catastrophic damage will occur”
Category 5 – maximum sustained surface winds at > 156mph.
“Catastrophic damage will occur”
As you can see the criteria that categorizes hurricanes. The above image is the satellite view of Hurricane Katrina before it hit the gulf coast. You can clearly make out the very defined eye wall in the center. This is where the system rotates around.
The life blood of any hurricane is the warm waters of the tropics. This allows for constant convection where the warm moisture rich air is lifted from the sea and is condensed by the cold air aloft. Just like any thunderstorm.
This hurricane season has started off slow, however the factors in the tropics are far more favorable for tropical cyclone development and our season should still see a slightly above average hurricane season. Below is the names of the storms the National Hurricane Center will use for this year.
Forecaster: Ian Mauger
Wyoming Valley PA Weather
24 AUG 2016 0320z
Pocono Lake Region WX 