Atlantic hurricane tipping points: CSU wavers if sea temps trump El Niño

The Atlantic hurricane season may be more subject to the storm-supportive effects of warm surface sea temperatures, leaving El Niño conditions less capable of delivering a calm storm season than originally hoped, analysts at Colorado State University have said to justify an increase in their forecast for storm activity in 2023.

The CSU’s Tropical Weather & Climate Research department upped its core forecasts for the season by about a quarter and now sees “a near-average Atlantic basin hurricane season” for 2023.

As with other major forecast centres, CSU is torn between the storm-suppressive effects of a forecast shift into El Niño and the storm-supportive effects of record warm Atlantic sea surface temperatures.

“The big question marks with this season's predictions revolve around the strength of El Niño and how anomalously warm the tropical and subtropical Atlantic is for the peak of the hurricane season,” authors say.

With opposing drivers facing off in a relatively unprecedented match-up, CSU warns of “greater-than-normal uncertainty” to the outlook.

On the bottom line, CSU upped its forecast for accumulated cyclone energy (ACE) for the season by about a quarter to a reading of 123 to match the 1991-2020 average.

CSU bumped its forecast for named storms by one to 14, hurricanes from six to seven and major hurricanes from 2 to 3, all closing the bulk of the gap in CSU forecasts to the longer-term average.

Tropical Pacific conditions have hit the El Niño threshold after a long three years of La Niña and conditions remain “conducive” for its further development. El Niño looks “imminent,” but its intensity “remains uncertain.” It’s not on track for peak years like 1997 or 2015, analysts note.

But sea surface temperatures in the Atlantic and Caribbean are breaking new ground at a 30-year record high. The next five warmest years include four years classified as hyperactive Atlantic hurricane seasons by NOAA.

But none of those years had El Niño conditions, making the match-up of opposing drivers seemingly unprecedented.

An initial set of forecasts out in mid-April had shown more confidence that the "robust" El Niño expected for peak season would create the wind shear needed to overcome the impact of warm sea surface temperatures.

The June 1 update puts CSU more closely in line with forecasters at the National Oceanic and Atmospheric Administration (NOAA) who have also warned that wildcards are endemic to seasons with such a mixed set of drivers as 2023.

The ever-uncertain landfall probabilities in the early view are only fractional changes from the April view and right at the historic average. CSU sees a 43% chance of major hurricane landfall on US coastline, a 21% chance of an east coast landfall and a 27% chance of a Gulf coast landfall, all matching the 140-year averages.

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