Well every year, in the summer and in the fall we have to think about hurricanes and we know that they can affect Eastern North Carolina but what we may not know is how hurricanes form and where do they form. Well for that we have head all the way across the Atlantic Ocean into the continent of Africa. It all starts with the monsoon. We start to see in this green here, the rains start to come into Africa and these thunderstorms really start to ramp up. These are strong to severe Thunderstorms that start in the central part of Africa. Well the hot and drier air from the north then combines with the hot and humid air coming in off of the Atlantic and they form this monsoonal trough or this coming together of winds and create an area of low pressure and uplift and we call this the inter-tropical convergent zone because we’re in the tropics here and the equator is just to the south so we’re really warm and humid. These thunderstorms like to ride along this monsoonal trough and then not unlike the thunderstorms that form in eastern North Carolina that hit the gulf stream waters, the warm Gulf Stream waters, once these thunderstorms hit the warm Atlantic Ocean they then begin to explode like a bomb and tower with towering thunderstorms. The northeast trade winds then start to push these storms across the Atlantic. These storms, at times, do grow very large and they then begin to spin around this area of low pressure that forms. Just to the north is a subtropical high. If we don’t allow that subtropical high to influence these storms, they can become tropical storms in nature.
Alright, you’ve already seen satellite pictures and radar pictures of hurricanes looking very pretty from the sky but let’s take a cross section of a hurricane and see exactly how they form. Here’s the warm moist ocean air. We usually use a threshold of 80 degrees and more as warm ocean air. They really need that warm ocean air to soak up all of that moisture that then begins to feed these towering thunderstorms. Then we have the top of the storm, cool dense air begins to sink in the middle of the storm. This is the eye right here and this is where it is calm. Sinking, subsiding air with the high pressure usually means calm conditions. We then begin to get that spiral and here are the rain bands where we’re just looking at rain and it’s not as intense as this eye wall here. Speaking of eye wall, we’re gonna talk about the hurricane anatomy.
Because that’s where we see the eye, and that’s where we see the eye wall. The eye wall is the most intense part of the hurricane. That’s where we see the highest winds and possible tornadoes and then we see storm surge, large swells across the ocean that floods when it comes on shore. Spiral rain bands also providing some heavy rains for us at times during the hurricane.
But the hurricane constantly needs this fuel, this warm ocean air, warm and humid air to rise up into the thunderstorms and allow them to grow large enough to become very towering and very dangerous. Then, they are also steered by the light external winds, the northeast trade winds. If these winds become too large and they start in different directions then that’s where we get the shear and the hurricane could destruct.
Speaking of hurricane destruction, this is one thing that can cause the hurricane destruction, it feeds off the warm ocean waters, so if we get a cool sea surface temperature below 80 degrees and more than that starts to destroy the hurricane. Also the strong external winds coming from different directions begin to shear the storm away and really begins to break it down. If we get some drier air coming in from that subtropical high in the northern Atlantic that also begins to break the storm apart.
So we really have to be careful and make sure that none of these names really get into our vocabulary in 2015.