Hello all! We are in the peak of hurricane season, which runs June 1st-November 30th. This year, we have Hurricane Dorian, currently forecast to be a Category 4 at landfall. Let’s take a look at how Dorian formed, and what he’s planning on doing…
There are three types of cyclones that can form: tropical, extratropical, and subtropical cyclones. Hurricane Dorian is a tropical cyclone, which is a warm core, non-frontal low pressure system of synoptic scale (about the horizontal length of 1,000 kilometers from the ground) that develops over the tropical or subtropical oceans. The temperature of the core is vital in determining if the system is a tropical or extratropical cyclone especially as we get later and later into the hurricane season (think September/October and beyond).
In order for a hurricane to form, many scientists have a different number of important factors, but we like to reduce it down to three key elements:
- Sea surface temperatures: ideally, we need warm sea surface temperatures above 26°C.
- Weak upper level winds in the atmosphere.
- Some sort of disturbance to provide low level convergence and rotation
So, where exactly have all the hurricanes been this year? We’ve been in an El Niño, which means waters around the equator off of South America have been warm and usually indicates a normal hurricane season. It is also possibly linked to this year’s spring severe weather outbreaks in the Southeast United States because El Niño conditions help to speed up the subtropical jet stream. We’re currently almost in La Niña conditions, which means those water temperatures are slightly cooler than normal. For much of the summer, there was a strong high pressure system over the Atlantic, which caused warm air to flow over Greenland (leading to the big ice melt we heard about last month) and cool air off of the coast of Africa pushed cooler water into the Main Development Region (the MDR, or the region between 10 and 20 degrees north in the Atlantic). This explains why we’d only heard about the Pacific named systems; the water over there was much warmer than on our side of the continent.
For Dorian, the eye initially dissipated south of St. Lucia and redeveloped west of Martinque, explaining the jog north in its initial path. From there, it went east of Puerto Rico and developed a dry slot to the north due to the running of air up the mountains and sinking down the other side. What’s next for Dorian? Initially, it was projected to make landfall near Jupiter, Florida along the southeast coast, but models are predicting a shortwave trough to exit the Ohio Valley region and weaken the high pressure system, causing Dorian to possibly turn north towards South Carolina. Dorian will move over sea surface temperatures near 30°C and is currently moving at 8 mph. No matter the exact path, areas within the cone of possibility could face a great amount of flooding and wind damage.
Just because Dorian is NOT currently forecast to make landfall in Florida doesn’t mean Florida is safe from harm. Dorian could have impacts over a large area, and if he makes it close enough to the coastline, cities like Fort Lauderdale, Daytona Beach, West Palm Beach, and Jacksonsville could still see near-hurricane force winds and storm surge, along with flooding for the main risk. Labor Day weekend hurricanes are not uncommon in the least: more than two dozen hurricanes have hit over the holiday weekend since 1851 (for more reading on this: https://time.com/5666204/florida-hurricanes-labor-day-history/). For official updates, follow the National Hurricane Center at www.nhc.noaa.gov.