Forecasters on Saturday described Tropical Storm Katia as “overachieving” in the Eastern Atlantic, saying that though its direction was proving difficult to pin down, it was expected to weaken on Sunday.
In an advisory late Saturday, the National Hurricane Center estimated that the storm had sustained winds of 45 miles per hour, with higher gusts. The storm, which was about 855 miles north-northwest of the Cabo Verde Islands, is not expected to pose a threat to land.
As for where Katia might be headed in the next couple of days, the Hurricane Center said “the guidance suite literally has motions in all cardinal directions,” with one forecast model showing “the proverbial squashed spider pattern.”
“Thus, the new forecast stalls the system before dissipating, but it will require some time to sort out the long-range details,” forecasters added.
In late May, the National Oceanic and Atmospheric Administration predicted that there would be 12 to 17 named storms this year, a “near-normal” amount. On Aug. 10, NOAA officials revised their estimate upward, to 21 storms from 14.
There were 14 named storms last year, after two extremely busy Atlantic hurricane seasons in which forecasters ran out of names and had to resort to backup lists. (A record 30 named storms took place in 2020.)
This year features an El Niño pattern, which arrived in June. The intermittent climate phenomenon can have wide-ranging effects on weather around the world, and it typically impedes the number of Atlantic hurricanes.
In the Atlantic, El Niño increases the amount of wind shear, or the change in wind speed and direction from the ocean or land surface into the atmosphere. A hurricane needs a calm environment to form, and the instability caused by increased wind shear makes those conditions less likely.
At the same time, this year’s heightened sea surface temperatures pose a number of threats, including the ability to supercharge storms.
That unusual confluence of factors has made solid storm predictions more difficult.
“Stuff just doesn’t feel right,” Phil Klotzbach, a hurricane researcher at Colorado State University, said after NOAA released its updated forecast in August. “There’s just a lot of kind of screwy things that we haven’t seen before.”
There is a consensus among scientists that hurricanes are becoming more powerful because of climate change. Although there might not be more named storms overall, the likelihood of major hurricanes is increasing.
Climate change is also affecting the amount of rain that storms can produce. In a warming world, the air can hold more moisture, which means a named storm can hold and produce more rainfall, like Hurricane Harvey did in Texas in 2017, when some areas received more than 40 inches of rain in less than 48 hours.
Researchers have also found that storms have slowed down, sitting over areas for longer, over the past few decades.
When a storm slows down over water, the amount of moisture the storm can absorb increases. When the storm slows over land, the amount of rain that falls over a single location increases.
In 2019, for example, Hurricane Dorian slowed to a crawl over the northwestern Bahamas, resulting in a total rainfall of 22.84 inches in Hope Town during the storm.
Other potential effects of climate change include greater storm surges, rapid intensification and a broader reach of tropical systems.