Enlarge /. Hurricane Isaias passed north of Haiti and the Dominican Republic on July 31 before whirling up the east coast.
The hurricane season in the Atlantic has been quite active so far. Nine storms chewed through the alphabet – two of them (Hanna and Isaias) reached the strength of a hurricane before landing. Unfortunately, this pattern will not subside as the outlook for hurricanes has increased the chances that this highly active season will continue. In fact, NOAA suggests that we could consider names that start with Y before things calm down for the winter.
In May, the NOAA outlook for the hurricane season gave a 60 percent chance of above-average activity, with about 13 to 19 named storms, six to 10 hurricanes, and three to six major category 3 or higher hurricanes.
On Thursday, the NOAA released an updated outlook with higher probabilities. "The season is expected to be one of the more active in the historical record," she says. The outlook now foresees between 19 and 25 named storms and seven to eleven hurricanes, although the number of large hurricanes remains unchanged. Because the potential energy available for storms can produce one or more smaller storms, the total is often calculated as "accumulated cyclone energy" or ACE. An above-average hurricane season reaches 120 percent of the middle ACE, while deleting 165 percent defines an extremely active season. The new outlook provides that the 2020 season will reach between 140 and 230 percent of the average ACE.
Nine names, but possibly a lot more …
A number of factors affect hurricane activity in the Atlantic, so there are several reasons for this activity outlook. First, ocean surface temperatures in the Atlantic are warm and provide an important ingredient for hurricanes – water vapor to fuel a storm. Wind patterns are still conducive to both creating new storms and strengthening existing ones. These include winds around the West African monsoon that help create low pressure systems that can trigger a tropical storm. This also includes weak wind shear, the contrast between low and high wind speeds that can cause a tropical storm to prevent and lose its organization.
Finally, the prospects in the Pacific Ocean have moved in the direction of La Niña conditions that developed this fall. The Pacific has been in a neutral state between clear La Niña or El Niño for over a year, but things tend to cooler waters in the eastern Equatorial Pacific, which drives the resulting atmospheric patterns. La Niñas tend to promote weak wind shear over the hurricane region of the Atlantic, which supports hurricane development, while the conditions in El Niño have the opposite effect.
A group at Colorado State University, which also makes hurricane season forecasts, has also updated its numbers this week, as it did in June and July. The researchers' central estimates now amount to around 24 named storms, 12 hurricanes and five large hurricanes. And with more activity, they find an increased likelihood that hurricanes will land.
However, all of these prospects are only probabilistic statements about the conditions for potential hurricanes and not forecasts for certain storms. Variable weather patterns determine how storms actually develop and intensify and the ways in which they follow. However, it is clear that despite the desire to take a break in a tough year, the ingredients are there for much more dangerous storms this year. This is a good reminder to make sure you are prepared if you live in a hurricane country.