How to Track a Hurricane
Hurricanes are a sensitive subject on the campus of Toccoa Falls College as of late. With hurricane Irma tearing its way through the area last year, the incoming threat Hurricane Florence this year, and seeing the aftermath of Hurricane Michael just this week, tropical storms are no longer foreign to anyone on campus. Last year, classes were canceled in response to the storm, but this year the predictions of the hurricane were never realized for the Toccoa area. In fact, in many areas, the forecasts for Hurricane Florence were wrong or significantly exaggerated. While the hurricane caused an enormous amount of damage in areas it did hit, the storm turned out to be far less severe than predicted. This leaves us with the question: why were the forecasts for Hurricane Florence so far off?
Hurricane tracking is complex. It involves many different factors, such as wind and rain intensity, barometric pressure, and temperature to make one forecast. This forecast may or may not change based on ever fluctuating weather patterns. Meteorologist use satellite, Doppler radar, and reconnaissance aircraft to track hurricanes. While there is always room for improvement, storm technology has come a long way since tracking hurricanes by word of mouth. Satellites are used to track forming storms and give general location, but they are limited in the information they can provide. Doppler radar is used for tracking storm intensity as well as the location of the eye of the storm. It is vital to track the location of the eye of the storm due to the peak wind speed and sudden pressure change between the eye and the storm wall surrounding it. This makes the eye wall the most dangerous component of the storm since it is the peak wind speed and barometric pressure. Radar can track rain intensity from 200-250 miles away (1). Radar can also help to locate the eye of the storm as well the intensity. However, all of this is just an educated guess until it can be observed in person. This is why meteorologists still use reconnaissance aircraft. Even though the air craft cannot get very near to the storm, they can give specifics on locations, intensity, and barometric pressures leading up to the eye wall. When combined, these factors are what determine category level, as well as projected pathway.
Initial forecasts for Florence predicted a category four hurricane making landfall in the Carolinas, but right before the storm made land fall, it dropped to a category two.
Hurricane categories are defined by wind speed (See Above). Initially Florence had sustained wind speeds of upwards of 140mph, making it a category four storm. Temperature of the ocean as well as the surrounding atmosphere, along with pressures of surrounding wind systems effect a hurricane’s intensity. Florence’s initial wind speeds of about 140mph dropped down to 90mph as it made landfall, bringing it down from a category four to category two.
The hurricane’s initial intensity is due to the unusually warm temperature of the Atlantic Ocean. Ocean temperatures have been increasing over the past few decades. The release of more heat into the atmosphere has affected the temperature of the ocean, and in turn the intensity of storms. Hurricanes always start as a smaller storm which gains strength from the warm surface of the ocean, evaporating surface water to build momentum. Thus, hurricanes gain their strength from warm waters. As the water evaporates, storm clouds form in the upper atmosphere. This causes rain, and in turn, the release of more heat which starts the process all over again. As the water gets warmer, more moisture evaporates into the air. This process increases in an exponential fashion with each cycle of precipitation and evaporation. Unless this cycle is broken by dry air, cold water, or landfall, a storm will continue to build. Storms begin to spiral from the rotation of the earth and then form hurricanes. This process occurred in the Atlantic Ocean for a prolonged period of time, causing Florence to grow into a category four hurricane. The question is: why did the storm’s intensity drop so rapidly before it made landfall?
Hurricane tracking technology has developed rapidly over the years, however its precision still has a great deal of room for improvement. Small changes in pressure or humidity cannot be tracked, but have the potential to drastically change a hurricane. It is thought that before landfall, Florence hit a dry spot of low humidity. This caused a break in the intensifying moisture and slowed the storm enough to bring it down to a category two. The storm may have also been weakened by moving over the barrier islands. Since the islands broke the hurricane’s contact with the warm water, the storm’s intensity would have decreased. While there was still substantial damage to the areas affected, the storm’s impact was significantly less widespread and less drastic than was originally predicted. So, the forecast can only be as good as the technology. This means that if you or your loved ones are in the predicted path of a hurricane, it is important to keep up with forecasts, as they can change in the blink of an eye. For those around the Toccoa area, it will be especially crucial to keep an eye on the weather forecast in the next few days as Hurricane Michael makes landfall.
References:
Tracking Hurricanes (2013).
W. Drye, What Forecasters Got Right and Wrong About Florence (2018).
Hurricanes form over tropical oceans, where warm water and air interact to create these storms.
R. Arnold, Hurricane Florence Viewed from the Space Station (2018).
K. Schallhorn, Hurricane Florence reminds Carolinas of Hugo, other major storms (2018).
Hurricane Michael Forecast to Intensify and Bring a Dangerous Threat of Storm Surge, Damaging Winds to Florida Panhandle; Hurricane Warnings Issued (2018).
Saffir-Simpson Hurricane Wind Scale.
Pressure and Winds.
Fuel for the Storm.
Sea Temperature Rise (2010).