• Why are a few clouds over northern Georgia being called a tropical disturbance?

Why are a few clouds over northern Georgia being called a tropical disturbance?

Jul 9, 2019

Over the past two days there has been an increasing amount of attention given to a tropical disturbance that is expected to make landfall on the upper Texas Coast or Louisiana by the end of the week.

StormGeo is currently referring to the storm as Disturbance 12, but it is likely that it will become Tropical Storm Barry. However, the disturbance is unusual in that it is:

  1. Currently over land
  2. Far from any ocean
  3. Not presenting itself as a tropical disturbance on radar or satellite imagery (currently no wind or rain activity).

What's going on?

It’s not unusual for tropical systems to get their start over land as low pressure systems. While over land, these systems are typically not referred to as tropical. As the system moves over the warm waters of an ocean, they can develop into tropical disturbances. These systems of atmospheric instability draw energy from the warmth of the water, allowing the circulation to grow into a disturbance, depression, tropical storm or hurricane. Some examples of this are:

  • Hurricane Alicia, 1983: The powerful and devastating Hurricane Alicia started as an area of weak low pressure on a cold front spanning from New England to Mississippi that moved into the Gulf of Mexico where it strengthened.
  • Surprise Hurricane, 1943: What’s known as the Surprise Hurricane of 1943 was initially identified as an atmospheric circulation over the southeastern U.S. that moved into the Gulf of Mexico where it took on tropical characteristics. Two days later it strengthened to a tropical storm and one day after that it developed into a hurricane. [Interesting side note: this hurricane was the first ever penetrated by an aircraft for the purpose of hurricane reconnaissance].

These storms were not classified as tropical systems until they moved over water and began to take on tropical characteristics.

What’s special about Disturbance 12?

All computer models and StormGeo’s tropical meteorologists are confident that Disturbance 12 will move southward across Georgia towards the Gulf of Mexico, where it will become a tropical storm. However, there is currently no system—tropical or otherwise, meaning there is quite a bit of uncertainty as to what exactly will happen with the disturbance. How strong it will be? When and where will it make landfall? How much rainfall will there be? These questions cannot currently be definitively answered.

Going Viral

Another unusual factor of Disturbance 12, especially compared to the storms from 1983 and 1943, is the high level and speed of modern communication, as well as the vast amount of available weather data. Although the future tropical storm is currently just an indication on computer models, the storm is already well-advertised. As a science, meteorology has developed dramatically in the past few decades, but so too, has social media. In the past, meteorologists would sit on a hunch for a day or two while waiting for the next set of data or run of the models to increase their confidence.

Today’s advances in technology allow a wider array of people – smaller weather organizations, amateur meteorologists and hobbyist – to have access to advanced weather data in addition to the pros. In the age of social media, all of these voices are contributing their opinions and forecasts in an attempt to boost followers and shares. With so much data and opinions available there is the possibility that the forecast can become diluted or lead to hype. It also has enabled us to give greater warning time, allowing people to prepare their homes and businesses, or even evacuate if necessary.

With this in mind, it’s easy to understand how a system that is only just starting to develop—and is far from any ocean—is already being called a tropical disturbance.