Atlantic set for rugged September, but full-year warnings ring hollow: CSU

The slow-go 2022 hurricane season can still put in a stretch of above-normal cyclone activity in the final two weeks of September, but the season as a whole can no longer live up to early fears, officials at the Colorado State University’s Tropical Weather & Climate Research department have said.

“We believe that the next two weeks have the highest probability of being in the above-normal category,” CSU researchers said of the two weeks to end-September. “Large-scale atmospheric conditions do look to favour heightened activity over the next two weeks.”

That “highest probability” for an activity level defined as accumulated cyclone energy (ACE) in excess of a 26 reading, is now put at 50%. Researchers give 40% chances to a “normal” level of 10 to 26 ACE.

The recently formed tropical storm Fiona looks set to hit hurricane status in the coming week, CSU said of its readings. NOAA has recently set a tropical storm warning for the leeward islands and a watch for Puerto Rico and both the US and British Virgin Islands.

Researchers see “some support” in the models for development of two additional areas in the next ten days.

The Madden-Julian Oscillation (MJO), a moving pattern of atmospheric variability over the east Atlantic said to create supportive conditions for storm systems, failed to meet prior forecast and remains “weak” and should remain so for the coming two weeks.

But wind shear, known to hinder cyclone development, will likely be less favourable over the coming period, models also suggest.

Even a high intensity end to September is unlikely to put the season on track for the above-normal activity levels forecasted throughout the spring and summer.

“While the most recent seasonal forecast called for an above-average season, the odds of reaching above-average seem quite unlikely at this time,” analysts wrote.

The first half of September finally delivered CSU researchers a bullseye, with tropical storms Danielle and Earl rendering enough ACE to meet the CSU forecast for “normal” levels vis-a-vis seasonal averages. Danielle and Earl didn't manage a landfall, but did deliver 27 ACE.

When CSU last offered a full-season forecast, the Atlantic was said likely to deliver 18 named storms and a total of eight hurricanes, of which four could hit category 3 or higher.

That Atlantic will now have to deliver another 12 named storms and six hurricanes to redeem the CSU crystal ball.

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