Has anything changed with seasonal hurricane forecasts since the start of the Atlantic hurricane season?
It is now late June, and many different groups have issued seasonal hurricane forecasts for the 2019 season. The Tropical Meteorology Project at Colorado State University (CSU) released their most recent outlook on Tuesday, June 4. At that point, they called for a near-average season of 14 named storms, 6 hurricanes and 2 major (Category 3-4-5 hurricanes; maximum sustained winds >=111 mph). That compares with the long-term average of 12 named storms, 6 hurricanes and 3 major hurricanes.
One of the big questions that CSU and many other groups issuing seasonal hurricane outlooks (such as the National Oceanic and Atmospheric Administration (NOAA)) raised were how the weak El Niño conditions that were currently observed might transition by the peak of the Atlantic hurricane season during August-October. El Niño is warmer than normal water in the eastern and central tropical Pacific. When it is present, it tends to increase upper-level winds in the Caribbean and the tropical Atlantic, tearing apart hurricanes and causing a less active season. Recently, NOAA scientists issued an updated outlook for El Niño. They gave a 55% chance that El Niño conditions will persist through August-October (Figure 1). These are the three peak months of the Atlantic hurricane season.
So What’s Changed?
At the start of the hurricane season, water temperatures across the tropical Atlantic were near their long-term averages. Over the past few weeks, the tropical Atlantic water temperatures have remained near normal (Figure 2). Warmer-than-normal water temperatures in the tropical Atlantic provide more fuel for hurricane (which live off of warm ocean water). They also are associated with a more unstable atmosphere and more moisture, which are critical for hurricane formation and maintenance. Near-average water temperatures are typically associated with near-average seasons, provided tropical Pacific water temperatures are also near their long-term averages.
Current conditions are fairly similar to what was observed at the start of the hurricane season several weeks ago. Consequently, it seems unlikely that CSU (or other groups) will be making large changes to their forecasts in the short term. CSU will be releasing its next update for the hurricane season on Tuesday, July 9.
Another important item to note is that while the Atlantic hurricane season has gotten off to a quiet start, hurricane activity during June is a very poor predictor of how much hurricane activity will occur during the remainder of the season. The hurricane season does not ramp up in an average season until early August. About 95% of all major hurricane activity after August 1 in an average year.
Lastly, it is important to note that regardless of any seasonal hurricane forecast, it only takes one hurricane making landfall near you to make it an active season. Residents and businesses are reminded to prepare the same for every hurricane season.
Figure 1: Latest forecast for El Niño from NOAA. They give a 55% chance of El Niño persisting through August-October (highlighted by the black arrow) – typically the three most active months of the hurricane season.