Tropical Storm Adrian Forms, Earliest Known Storm in Eastern Pacific

Update: Due to strong wind shear, Adrian was downgraded to a tropical depression late Wednesday and is no longer expected to become a hurricane or re-strengthen into a tropical storm.

Tropical Storm Adrian became the earliest known tropical storm to form in the eastern North Pacific on Wednesday, six days before the official May 15 start to the season.

This is also the first time in the satellite era where early storms formed in both the Atlantic and eastern Pacific — Tropical Storm Arlene formed in the Atlantic as a fairly rare April storm.

While such early storms can, and have, happened, there are some signs that they could happen more as the world warms and the overall hurricane season lengthens. But not all the evidence bears that out and the question remains a compelling subject of research.

Adrian formed off the coast Central America early Wednesday evening thanks in part to an abundance of warm ocean waters, Phil Klotzbach, a Colorado State University hurricane expert, said in an email.

Such warm ocean waters this time of year aren’t unusual, and it was those combined with lower than normal wind shear that helped Adrian coalesce. Wind shear happens when the winds at different levels of the atmosphere are blowing at different speeds and in different directions.

Shear in the atmosphere has since ramped back up, though, Klotzbach said, and Adrian is looking a little ragged because of it.

The National Hurricane Center expects Adrian to slowly strengthen over the next few days as it moves to the northwest, paralleling the Central American coast. It could become a hurricane by the weekend. It is currently not a threat to land.

Adrian is only the third storm to form before the May 15 start to the eastern North Pacific hurricane season. The other two times this happened were in 1990 and 1996, Klotzbach said.

An earlier storm isn’t necessarily an indicator of a busy season, though there is some research that suggests more storms are correlated with a longer season and vice versa.

Klotzbach’s early forecast for the 2017 Atlantic hurricane season is for a slightly below-average season, with 11 named storms, of which four would become hurricanes. (The 1981-2010 median values are 12 named storms and 6.5 hurricanes.)

Klotzbach will update his forecast on June 1, the official start date for the Atlantic season. The National Oceanic and Atmospheric Administration will issue its forecasts for both the Atlantic and eastern Pacific later this month.

Whether global warming might impact the length of the hurricane season is something scientists have only just begun to investigate. The idea is that because the oceans absorb the bulk of the excess heat trapped by the buildup of greenhouse gases in the atmosphere, it may make tropical cyclones more likely to form at previously marginal times of the year.

Jim Kossin, of the University of Wisconsin and NOAA, has found some evidence for a lengthening of the Atlantic season in observations. The eastern Pacific, though, doesn’t seem to show a significant trend, Klotzbach tweeted. Climate models have also been mixed on that score.

Overall, research points to warming leading to fewer storms overall, but to more of those storms being strong ones.