Chances that the global climate pattern El Niño will develop this fall were increased in the most recent forecast, boosting confidence in revised predictions for a below-normal hurricane season.
The federal Climate Prediction Center’s July El Niño forecast is giving it a 65 percent chance of appearing in the fall, and about a 70 percent chance of a winter formation.
That’s up from a June forecast that predicted a 50 percent chance of a fall arrival, and a 65 percent chance of wintertime development.
“Those are fairly strong numbers and the trend certainly is for continued warming in the Pacific,” said Jeff Weber, an atmospheric scientist with the University Corporation for Atmospheric Research, about the new forecast. “If that plays out, it really could help to shear apart those late-season hurricanes that come off the African coast.”
For Florida, the periodic warming of the equatorial Pacific Ocean can mean a less active hurricane season with fewer of the powerhouse Cat 5 tropical cyclones known to build during the peak months of August through October.
Earth was put on an El Niño watch last month, but it’s not officially declared present until ocean temperatures in the equatorial Pacific are more than 1 degree above normal and are expected to maintain that temperature for six months.
After that, it can take 30 to 60 days for the atmosphere to respond, Weber said.
“Generally speaking, we think El Niño should show every four to eight years, so we are seeing now a separation of just a couple years,” Weber said. “But we really don’t have a long enough record of this to cipher out what’s normal.”
The last strong El Niño was in 2015 and 2016.
The onset of El Niño occurs in tandem with the relaxation of the trade winds — those Earth-skimming easterlies that have guided sailing ships across the world’s oceans for centuries.
With the trade winds reduced, warm water that has piled up in the western Pacific Ocean and around Indonesia rushes back toward the east. That movement of warm water shifts rainfall patterns and the formation of deep tropical thunderstorms. The exploding storms whose cloud tops can touch the jet stream disrupt upper air patterns so winds come more out of the west.
The west winds create shear in the Atlantic, which can be deadly to budding hurricanes.
Earlier this month, Colorado State University reduced its hurricane season forecast to 11 named storms, four hurricanes and one major hurricane of Category 3 or higher.
The team’s start-of-season forecast issued on May 31 had called for 14 named storms, six hurricanes and two major hurricanes.
An average hurricane season has 12 named storms, six hurricanes and two major hurricanes.
The National Oceanic and Atmospheric Administration’s May 24 hurricane forecast called for between 10 and 16 named storms, five to nine hurricanes and up to four major hurricanes of Category 3 or higher. NOAA will issue an updated forecast in August.
“El Niño or not, we are predicting a lot of storms, so people should not take the potential El Niño as a signal not to be prepared,” said Gerry Bell, NOAA’s lead seasonal hurricane forecaster, in a June interview. “That’s a very important part of this, no one is saying the season will be shut down.”
Already three named storms, including two hurricanes — Category 1 Beryl and Category 2 Chris — have come and gone.
Also, accumulated cyclone energy this season stands at 14.4 when the average for this time of year is 5.1. Accumulated cyclone energy, or ACE, is a way to measure the strength and longevity of tropical cyclones.
“So in terms of ACE, we are at 326 percent of normal activity for the date,” said University of Miami senior research associate Brian McNoldy in a blog last week. “Another way to frame it is that the ACE is currently what it climatologically would be on August 14.”
The last time the Atlantic basin mustered two hurricanes so early in the season was during the hyperactive season of 2005, McNoldy said.
While El Niño can protect Florida from hurricanes during storm season, it also tends to mean a wetter, cooler winter.
“You might save some moisture from fewer hurricanes, but then you get increased moisture in the winter from El Niño,” Weber said. “Sometimes those rain events can be more impactful than what you’ll see from a small hurricane.”