Government forecasters on Thursday doubled the odds of above average Atlantic hurricane activity from previous forecasts issued in May, citing unprecedented warmth across Atlantic waters holding back the usual storm-suppressing influence of El Niño.
The new forecasts from NOAA – the parent agency of the National Weather Service – came a week after forecasters at Colorado State University – the pioneers of seasonal hurricane forecasts – issued their final outlook of 2023, predicting above average activity for the peak months ahead. Both high-profile forecasts were released only weeks ahead of what’s typically the busiest stretch of the Atlantic hurricane season.
El Niño conditions – the abnormal warming of waters across the eastern Pacific around the equator – have been building for months. Over the past month, waters across the main El Niño monitoring region (a region known as Niño 3.4) have averaged about 1.1°C (2°F) above the 30-year (1991-2020) average. This may not sound impressive, but it’s the ocean equivalent of a moderate fever. The threshold for weak El Niño conditions is 0.5°C (0.9°F) above average, with strong El Niño conditions starting around 1.5°C (2.7°F) above average.
Government experts on Thursday separately called for a strong El Niño by this winter.
El Niño begins in the ocean, but it eventually has a major influence on atmospheric circulations around the globe. This is how hurricane activity in the Atlantic can be reduced by a slight warming of the eastern Pacific. But not all El Niños are alike, and when exactly the ocean links up with the atmosphere matters for hurricane season impacts.
While we’re still in El Niño’s beginning stages, there is evidence that this summer it’s been slower to join hands with the atmosphere than during other recent episodes. We can see this in the abnormal patterns of rising and sinking air over the past month compared to other recent strong El Niños, like 2015 or 1997 in their early stages.
Notice that this July, the most pronounced area of rising air was farther west over the western Pacific instead of over the eastern Pacific near the abnormally warm waters, as we’d expect in a more textbook El Niño.
Of course, that doesn’t mean El Niño’s failing to link up with the atmosphere. It’s likely already occurring, and we can see signs of it now, but it does appear delayed relative to more recent episodes.
Additionally, the extreme warmth in the Atlantic may serve to counteract the usual moderating influence of El Niño on the Atlantic hurricane season. We’ve never observed Atlantic waters as warm as 2023 in any year, let alone during a potentially strong El Niño, so it’s uncharted territory. We can model how the two may interact, however, and our long-range models suggest little slowdown in the Atlantic.
The conflicting information means a wide range of forecast numbers from the two dozen or so groups specializing in seasonal hurricane forecasts. Both NOAA and Colorado State – while two of the longest-running and most skillful hurricane forecasters – remain on the high side of the seasonal forecast spectrum in 2023.
Regardless of how the numbers shake out this hurricane season, it only takes one hurricane to make a bad hurricane season. Seasonal forecasts are largely an academic endeavor and shouldn’t affect you or your family’s preparations.
As we discussed in yesterday’s newsletter, we’ll be watching the Atlantic a little more closely toward the end of next week, but for now, the tropics will stay mostly quiet for the week ahead.
