Times Staff Writers
The National Oceanic and Atmospheric Administration is now predicting an above-average hurricane season driven in part by warmer-than-normal water temperatures in the Atlantic Ocean.
The agency's updated 2017 Atlantic forecast, released Wednesday, should stand as a warning for coastal residents as we enter the most active period for hurricane development, forecasters said.
"Today's updated outlook underscores the need for everyone to know their true vulnerabilities to storms and storm surge," said Brock Long, administrator of the Federal Emergency Management Agency. "As we enter the height of hurricane season, it's important for everyone to know who issues evacuation orders in their community, heed the warnings, update their insurance and have a preparedness plan."
Forecasters now say there's a 60 percent chance of an above-normal season, "with the possibility now that it could be extremely active," said Gerry Bell, the lead seasonal hurricane forecaster at NOAA's Climate Prediction Center, which published the report. There is only a 30 percent chance for an average season and a 10 percent chance for a below-average season.
Those numbers are up from NOAA's May prediction of a 45 percent chance for an above-average season. Wednesday's forecast said it's likely there will be 14 to 19 named storms, with five to nine hurricanes and two to five major hurricanes this season, which runs through Nov. 30. It factors in the six named storms we've already seen this year, including Hurricane Franklin, which grew from a tropical storm to a hurricane on Wednesday while bearing down on the Mexican gulf coast.
A major hurricane is a Category 3 or stronger, with wind speeds of at least 111 m.p.h.
In May, NOAA predicted 11 to 17 named storms, with two to four major hurricanes. Its forecast of five to nine hurricanes remains unchanged since May.
The season, meteorologists say, has the potential to be the most active since 2010. An average season comprises 12 named storms, with six hurricanes, three of them major, according to NOAA.
Several factors have combined to make the tropical Atlantic conducive to hurricane development, said Bell, with NOAA's Climate Prediction Center. One is that El Niño, the phenomenon of warmer-than-normal water in the tropical Pacific Ocean, didn't materialize. That warmer water creates high-altitude winds above the tropical Atlantic, which contributes to wind shear that helps to keep thunderstorms from coalescing into cyclones.
Another factor, Bell said, is that the water in the tropical Atlantic Ocean is one to two degrees Fahrenheit warmer than normal, because the surface winds across that part of the ocean have been weak. Strong winds will churn water near the surface, said Phil Klotzbach, a climate research scientist at Colorado State University, which puts out its own hurricane seasonal outlooks. That churn results in cooler surface water. When the winds are weaker, he said, the top layer of water bakes in the sun.
The warm water doesn't just fuel hurricanes, Klotzbach said. It also lowers the air pressure over the water, making the atmosphere more unstable, which gives cyclones more opportunities for development. Also, he said, warmer water often contributes to more moist air, which is better for cyclones than drier air.
Klotzbach's most recent seasonal outlook, released Aug. 4, is similar to NOAA's, predicting 16 named stormed, eight hurricanes and three major hurricanes.
He said the six storms we've already seen — twice the average for this time of year — doesn't play a great role in forecasting the rest of the season. Most of those storms were weak and marginal, he said, and didn't contribute much to the expected seasonal total of accumulated cyclone energy, a measure that combines both the strength and duration of storms.
But Bell said what those storms indicate is that the conditions in the Atlantic hurricane basin for storm development are already set entering the peak of the season.
"The wind and air patterns in the area of the tropical Atlantic and Caribbean where many storms develop are very conducive to an above-normal season," Bell wrote in the news release.
Klotzbach said climate change likely hasn't played a role in the active seasons we've seen this year and last, in which Florida was hit by its first hurricane in 11 years. It's difficult, he said, to try to pinpoint climate change's effect on storms amid all the noise created by more influential weather factors, such as El Niño.
In general, Klotzbach said, science suggests climate change could actually decrease the frequency of hurricanes, but increase their intensity. But it depends how the planet, which warms unevenly, grows hotter.
"What really matters for tropical cyclones is how the Atlantic warms relative to the rest of the globe," he said.
Contact Josh Solomon at (813) 909-4613 or [email protected] Follow @josh_solomon15.