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September 9, 2024

A Quiet August in the Tropics...Will it Last?

This spring, forecasters across the country were calling for a record-breaking Atlantic hurricane season due to extremely warm ocean temperatures and a developing La Niña. While the 2024 season started off strong with Hurricane Beryl becoming the earliest Atlantic Category 5 hurricane on record, things were eerily quiet in August and the first week of September.

According to experts in the Atmospheric Science Department at Colorado State University, the culprit is likely a combination of factors.  

  1. Tropical waves are developing too far north. Typically, a northern shift in the monsoon trough would suggest an active hurricane season, but the tropical waves are emerging over cooler-than-normal waters off the northwest African coast. This northerly track can also help bring down dry air from the subtropics. Dry air hinders development of tropical cyclones.
  2. Warm temperatures in the upper atmosphere, near the jet stream, may be leading to a more stable environment. Stable environments can also hinder tropical cyclone development. However, this theory didn’t stop Hurricane Beryl from becoming the earliest category five hurricane one record.
  3. In August, the wind shear in the eastern Atlantic was too strong. Any tropical waves emerging off the African Coast struggled to strengthen due to wind shear hindering development.

Figure 1: The 100-year average of number of tropical cyclones by day. The yellow count represents hurricanes and the red count represents all named tropical cyclones including both tropical storms and hurricanes. Source: NOAA.

It’s important to remember that we still have about two-thirds of the hurricane season to go. The climatological peak of hurricane season is September 10 and September typically produces more landfalling storms in the U.S. than any other month.

Figure 2: Likely tracks of tropical cyclones in the month of September with orange showing the most likely tracks. Source: NOAA.

Wind shear is forecast to decrease for the second half of September, allowing more chances for tropical waves to develop into tropical cyclones. Additionally, NOAA predicts La Niña to develop in the next month or so. Sea surface temperatures are also very warm. These factors point to the potential for an active late hurricane season.

Figure 3: Graph depicting the percent chance of La Niña, El Niño, or neutral conditions. There is a 66% chance that La Niña develops in the September-October-November timeframe. Source: Columbia University.

It only takes one landfalling tropical cyclone for it to be an impactful hurricane season. Hurricane Beryl is a great example. Hurricane Beryl made landfall as a Category 1 hurricane near Matagorda, TX.  Beryl also spawned 17 tornadoes in Texas, Louisiana and Arkansas. More than 2.5 million people lost power due to the hurricane and unfortunately led to at least 23 heat-related deaths in the Houston area.

Hurricane season lasts through November 30. So, what about the rest of the 2024 hurricane season? NOAA updated their predictions on August 8 and the predictions are very similar to their original forecast. An active hurricane season is still forecast by NOAA.

 

Table 1: Hurricane statistics through August 2024.

Given relatively quiet conditions into the first week of September, it’s possible that NOAA’s predictions do fall short. However, a near-normal or slightly above-normal season could still happen. Will late September and October bring more tropical impacts to the U.S.? It is possible. Reach out to StormImpact to see how our Hurricane Outage Prediction Model can help you make data-driven decisions.

Meteorologist Meghan Klee is the Product Innovation Manager at StormImpact, with over a decade of experience in operational meteorology in the utility sector.

Sources:

https://tropical.colostate.edu/Forecast/2024_0903_seasondiscussion.pdf

https://www.cpc.ncep.noaa.gov/products/outlooks/Slide1.JPG

https://www.noaa.gov/news-release/highly-active-hurricane-season-likely-to-continue-in-atlantic

https://www.cbsnews.com/texas/news/heat-related-texas-deaths-climb-after-beryl-left-millions-without-power-for-days-or-longer/