From the early-season forecast to the scariest words in the forecast to the best days ahead, the Atlantic hurricane season will be based on a nearly 500-year trend.
Adaptive rain-shadow maps
United States NOAA forecast
“Strong El Niño and abnormally warm tropical Atlantic waters near the surface have put us on track for the 10th warmest Atlantic hurricane season in records going back to 1851,” said Gerry Bell, Ph.D., lead seasonal hurricane forecaster with NOAA’s Climate Prediction Center. “This year’s forecast models are pointing to a September-November period with below-normal named storms. However, if the Atlantic remains persistent with strong El Niño conditions, we may see more named storms in the final months of the season.”
El Niño event could affect hurricane season
Computer model ensemble outlook for the western North Atlantic for the period between September through November 2019. The westward-moving high pressure ridge is centered over the North Atlantic, and the dark blue represents more active conditions. Image courtesy of NOAA (NOAA)
El Niño’s forecast revision
NOAA’s Climate Prediction Center put out a June update on El Niño last month and trimmed its most likely time period of development to November from April.
El Niño plays a critical role in influencing Atlantic Atlantic hurricane activity. At this point in El Niño, water temperatures in the tropical Atlantic are warmer than average and computer models predict a stronger El Niño in the coming months. El Niño’s warm waters tend to weaken wind shear over the Caribbean Sea, increasing the overall influence of warm water in the Atlantic.
When there is high pressure ridge over the central and eastern Pacific, the atmosphere can’t make up the energy losses, which contribute to weaker intensity and storm tracks. Conversely, when there is a weak ridge over the central and eastern Pacific, the atmosphere can make up the energy losses, resulting in stronger intensity and storm tracks.
In other words, high pressure near the equator in the eastern Pacific can lead to a very strong El Niño in the Atlantic, while a weak ridge could lead to a more average El Niño.
This is a seasonal projection of El Niño as a strong signal for hurricane development and will influence the number of Atlantic hurricanes and the strength of those storms. A weak ridge in the central Pacific can also provide a boost for hurricane development, but no matter which way the ridge appears, it is up to the Atlantic basin to deliver.
One key to understanding the region is to look at the residual of the storm system after its initial landfall. We saw more than 300 named storms and tropical storms during the past year, some strengthening to Category 3 and Category 4 hurricanes. To summarize, of the 253 named storms that formed during 2018, 153 became hurricanes, 44 of those being major hurricanes (Bermuda hurricanes. Researchers have studied areas of the Atlantic before cyclones intensify. They found that a warm, moist atmosphere with weak downdrafts may provide an environment conducive to formation and evolve into a storm, while a cool, dry atmosphere with strong downdrafts may inhibit cyclone formation. In storms where a moderate degree of beach energy is emitted, a low pressure ridge across the equator may act as a “coat of steroids” and increase cyclone development. This storm system was known as Great Hurricane #1 and developed near Mayan Cay in the Caribbean.
Although there is no definitive long-term relationship between oceanic conditions and hurricane development, there are mechanisms through which climate change changes can influence an individual storm and potentially the whole Atlantic hurricane season. There have been 15 consecutive years of above average Atlantic hurricane activity.
Risk factors that could lead to some extra activity are subtropical or west-southwest currents off the Caribbean Sea and Caribbean island chain and the tropical Atlantic Ocean. The frequency of storms and tropical storms depends on these and other, commonly described, cyclonic dynamics in the Atlantic basin. However, the timing of these favorable cyclone conditions might vary more often for individual storms, rather than leading into greater probability of forming a storm.