 Discussion: As November comes to a close, so does the 2018 Atlantic Hurricane Season. This season produced fifteen named storms. Among those fifteen storms, eight of them were hurricanes. This hurricane season produced two major hurricanes out of the eight that formed. A major hurricane is defined as a category three or higher on the Saffir-Simpson wind scale. The Saffir-Simpson wind scale measures a hurricane’s sustained wind speed. This Hurricane season will be remembered in particular for Hurricanes Florence and Michael that caused significant damage to the southeastern United States. Hurricane Florence was one of two major hurricanes this season. It formed on August 31st, 2018 and as it made its way across the Atlantic it strengthened into a category 4 hurricane with sustained winds of 130 miles per hour. It maintained its strength until the track took the storm into an area of wind shear. Wind shear can tear apart the hurricane causing the structure to become asymmetrical and weaken. Florence made landfall in North Carolina on as a category one hurricane and moved slowly over the Carolinas producing torrential rainfall and devastating flooding. Many rivers across the Carolinas came close or actually broke their rainfall records. It took many weeks and in some places a month for the waters to recede and the rivers to fall below flood stages. Hurricane Michael was the second of two major hurricanes this season. It formed in the Caribbean Sea on October 2nd, 2018 and traveled slowly through the Gulf of Mexico. Once in the Gulf of Mexico, it rapidly intensified and became a major hurricane on October 9th, 2018. Hurricane Michael reached a peak intensity of a high-end category four hurricanes with maximum sustained winds of 155 miles per hour. On October 10th, 2018, Hurricane Michael made landfall on the Florida panhandle near Mexico Beach, Florida. Michael caused widespread damage across the panhandle with a fourteen-foot storm surge that washed houses away and strong winds that destroyed buildings and foundations. Michael was the fourth strongest storm to make landfall in Florida since Hurricane Andrew in 1992 in regard to its wind speed. It was also the third strongest hurricane in regard to its central pressure with a minimum central pressure of 919 millibars to make landfall since Hurricane Camille in 1969. Overall this Hurricane season was pretty active this year. Tropical Storm Alberto kicked the season off early on May 25th, 2018 making landfall in Florida. Seven of the fifteen named storms were subtropical at a point in their lifetime. A named storm that has characteristics of a non-tropical storm is called a sub-tropical storm. These seven storms this season all became tropical storms and three of them intensified to hurricane status. For the first time since 2008, the Atlantic saw four named storms existing in the Atlantic basin together. Florence, Helene, Isaac, and Joyce all co-existed for a period of time this season. With the 2018 Hurricane season finished, it is never too early to begin making preparations for next summer. It’s important to have a plan in place if you live in hurricane-prone areas because it only takes one storm to cause significant damage. Being prepared and tuned into your local and government weather service offices is a great way to be ready for the 2019 season! For more information on having a hurricane ready plan click here! To learn more about other tropical cyclone stories from around the world, be sure to click here! © 2018 Meteorologist Shannon Scully
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  DISCUSSION: Year in and year out, millions of people all over the world bear witness to the formation of tropical cyclones in tropical ocean basin across the globe. During some of the more intense tropical cyclones which form during a given year, there are often some neat satellite imagery-based signature features which can be greatly appreciated even by the general public. One such example of an interesting feature which will often occur in association with tropical cyclones of variable intensities, but most often in association with major hurricanes (i.e., across the tropical Eastern and/or Central Pacific Ocean as well as the tropical Atlantic Ocean is upper-level outflow.
Upper-level outflow associated with a tropical cyclone is particularly interesting since it will always flow in the opposite direction from the more intense cyclonic (anticyclonic) winds which occur with tropical cyclones which form within the Northern (Southern) Hemisphere. However, the big question which many people will often inquire about in association with upper-level outflow tied to more intense tropical cyclones is why the upper-level winds from in the opposite direction of the low/mid-level wind flow regime. As is often the case with many interesting scientific conundrums in life, the answer to this question is actually very simple. And that answer is a result of a basic atmospheric dynamics principle and fundamental law of atmospheric physics. This basic atmospheric dynamic principle is the fact that above any low-pressure center is a high-pressure center and above any high-pressure center is always going to be a nearby low-pressure center. Effectively, this fundamental principle is what allows the atmosphere to always remain at or closer to a dynamically-stable state of atmospheric balance over both shorter-term and longer-term periods. When it comes to observing upper-level outflow associate with a tropical cyclone via satellite imagery, it is often photogenic and almost mesmerizing to watch. Moreover, upper-level outflow is often found to be quite attention-grabbing despite the storm encapsulated within the symmetric outflow (or sometimes asymmetric outflow depending on the given situation at hand) being quite powerful towards the surface of the Earth. Thus, this just goes to show that even the more interesting and curious details of a larger weather event can be quite interesting to understand on a more profound level. To learn more about this particular issue, please also visit our GWCC Kid's Corner, which can be found right here! To learn more about other tropical cyclone events and topics from around the world, be sure to click here! © 2018 Meteorologist Jordan Rabinowitz |
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