Tropical systems in the Atlantic Ocean form due to warm air from the coast of Africa that meets the ocean breeze that allows for a storm to form. Through the time span of two to three weeks, tropical systems can go through different phases from tropical disturbance to a major hurricane. From the beginning of its lifecycle, Hurricane Dorian started out as a disturbance on August 19, 2019. Five days later, the system grew to a Tropical Depression and by August 29 the system grew into a hurricane. Beyond this time, Hurricane Dorian strengthened rapidly and made landfall on the US Virgin Islands before approaching Florida. In fact, Hurricane Dorian became a Category 5 on the Saffir-Simpson Scale, which is the highest possible tier, while making landfall in the Bahamas producing winds of upwards to 185 mph.
Photo: The lifecycle of Hurricane Dorian where each dot represents a 6-hour interval. (Photo from NOAA)
As a Major Hurricane, Dorian was approaching the Florida coast and was brought to a halt over the ocean, leading the public to question the time of arrival. Since the atmosphere can dictate the processes based on what is occurring hundreds of miles away, the common phenomenon called ‘blocking’ was taking effect stopping Dorian in her tracks. Blocking can cause systems to remain in their space for hours or days at a time. Considering the dynamics of a low pressure system, the winds move in a counter-clockwise and inward direction. As you may assume, a high pressure system is the opposite, where winds will move clockwise and outward. Based on the proximity of these systems, multiple high pressure systems can act as a block to a low pressure from moving in its predicted track. In the case of Dorian, the hurricane was stalled over the Atlantic Ocean, just outside of the Florida coast due to two large high pressure systems, one to the west and another to the east.
Photo: The forecast issues from WPC the afternoon of September 3, 2019 showing two high pressure systems to the east and west of the location of Hurricane Dorian. (Photo by WPC/SPC/NHC Forecasters)
Luckily, in the time the hurricane was stalled, Dorian experienced decreased intensity due to colder waters moving into the hurricane and differences in wind direction causing a loss of organization. As the Hurricane was soon able to continue towards the continental United States, Dorian made landfall in South Carolina as a Category 3 Hurricane. Beyond this, Dorian moved northeastward up the Atlantic coast of the United States and beyond before fully dissipating on September 10.
Despite the intensity and organization of a system, the atmosphere all works together. If a strong low pressure is moving in a direction that is halted by a high pressure system, it can easily stop in its tracks. This can be applied outside of tropical systems to any low pressure system that can lead to a prolonged period of reoccurring weather phenomenon (i.e. rain, snow, etc.) For this case, the Florida coast was saved from an intense storm that could have caused drastic damage and even through losing intensity, other states saw impacts. Being aware of the surrounding weather can be a decider on what happens in the expected track of a storm.
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©2019 Meteorologist Jason Maska