Impacts of Tropical Cyclone Stalling
11/2/24 – Numerous academic studies have found an increase in the number of storms with decreasing forward speeds, i.e., tropical cyclone stalling, when comparing recent decades with earlier periods.
Meteorologists call the distance that tropical cyclones travel in a given amount of time “tropical cyclone translation speed” or TCTS.
They have also found that TCTS is a key factor in determining the damage a tropical cyclone can cause to a community from rainfall, exposure to high winds, flooding and storm surge. That damage totals more than a trillion dollars in the last 40 years with death tolls in the thousands.
There is broad academic agreement on the increase in the number of slow-moving or stalling storms. And they identify the central Gulf Coast as one of the hot spots.
Some studies have also found a correlation between stalling storms and rapid intensification near coastlines, a red flag for emergency managers.
Rise in Economic Devastation and Fatalities
Marybeth Melcher of Western Michigan University published “Tropical Cyclone Translation Speeds in the Northern Atlantic Ocean.” She found statistically significant trends indicating an increase in the duration of cyclones (slowing of forward motion) over forty-years.
She says that regions experiencing tropical cyclones “will experience greater exposure to some of the most devastating aspects of tropical cyclones such as extreme rainfall, wind speeds, and flooding. Increased exposure to these elements could and will likely translate to a rise in both economic devastation and fatalities.”
Slowdown Found to Be Global
In a 2018 study called “A global slowdown of tropical-cyclone translation speed” published in Nature, James P. Kossin found that TCTS has decreased globally by 10% from 1949–2016. That includes a:
- 21% decrease over land areas in the western North Pacific
- 16% decrease over land areas affected by North Atlantic tropical cyclones
- 22% decrease over land areas in the Australian region.
Remember, the more time a storm lingers over any given area, the higher the rainfall accumulations.
Hurricane Harvey a Notable Example
Kossin also notes that “unprecedented rainfall totals associated with the ‘stall’ of Hurricane Harvey13,14,15 over Texas in 2017 provide a notable example of the relationship between regional rainfall amounts and tropical-cyclone translation speed.”
Kossin concluded that the “translation speed of tropical cyclones, particularly over land, is therefore highly relevant when considering potential changes in local rainfall totals.”
Recent Study Focused on Atlantic Basin
In September of 2024, Dr. Jill C. Trepanier, Dr. John Nielsen-Gammon, Dr. Vincent M. Brown, Derek T. Thompson, and Dr. Barry D. Keim published “Stalling North Atlantic Tropical Cyclones” in the Journal of Applied Meteorology and Climatology (© 2024 American Meteorological Society*.)
The authors found that TCTS influences rainfall accumulation, storm surge, and exposure to high winds. These effects are greatest when storms stall.
Trepanier and her colleagues provide both a definition and climatology of slow-moving or stalling TCs in the North Atlantic from 1900–2020. “A stall is defined as a tropical cyclone (TC) with a track contained in a circular area … with a radius of ≤ 200 km for 72 hours.”
The authors found that of 1,274 North Atlantic tropical cyclones, 191 or 15% met this definition. Of those, 10 stalled more than once. Hurricane Ginger in 1971 stalled the most with four separate stalls.
“Stalling TC locations are clustered in the western Caribbean, the central Gulf Coast, the Bay of Campeche, and near Florida and the Carolinas,” say the authors. “Stalling was most common in October TCs (17.3% of October total) and least common in August (8.2%).”
Their study examined two time periods, 1900-2020 and 1966-2020, and statistically tested for trends in the annual frequency of stalling storms.
The estimated annual frequency of stalls significantly increased from 1966–2020 by 1.5% per year. The cumulative frequency in the number of stalls compared to all storms also increased.
“Stalling storms have a significantly higher frequency of major hurricane status than non-stalling storms. Storms are also more likely to stall near the coast (≤ 200 km). Approximately 40% (n=77) of the stalling TCs experienced a period of rapid intensification, and five did so within 200 km of a coastal zone.”
The authors believe their findings will help emergency managers better prepare for the future. Speaking of that…
Stay Alert
Remember that hurricane season isn’t over until the end of November. The National Hurricane center shows three areas of activity in the Atlantic. They’re giving the closest one in the southwestern Caribbean an 80% chance of formation in the next seven days.
Don’t let your guard down yet.
Posted by Bob Rehak on 11/2/24
2622 Days since Hurricane Harvey
*Extensive quotes from abstract reproduced with permission of copyright holder.
