A key sign of hurricane activity has flipped into high gear
"One of the biggest changes I've observed in recent weeks is a considerable warming of the so-called Main Development Region (MDR) of the Atlantic above its seasonal averages," WPLG-TV hurricane expert Michael Lowry said in late July on a Substack post.
That's a big change from earlier this season.
"To open the hurricane season in June, waters across this bellwether part of the Atlantic where most of our strongest hurricanes get their start were running average to even below average," he said.
The Main Development Region (MDR), located between the Caribbean and Africa, is a region in the Atlantic where many tropical cyclones (tropical storms and hurricanes) form. This area is key because it's where many tropical waves, which can develop into hurricanes, originally form.
The warm water in that key region is just one of the reasons hurricane forecasters are warning that hurricane season could soon heat up.
Warm water everywhere
It's not only the Main Development Region that's warm: Water across the Gulf of America (formerly known as Gulf of Mexico) and the Caribbean Sea area also above average, scientists said. In fact, closer to home, persistent high pressure has led to some notable warming of the shelf waters around Florida, as well as the nearby southwest Atlantic, Andy Hazelton, a hurricane scientist at the University of Miami, pointed out on X on August 1. This included a 90-degree reading at a buoy near Virginia Key, Florida, near Miami.
"Water temperatures are pretty much warm enough everywhere in the tropical Atlantic to support hurricane formation," Colorado State Univerisity meteorologist Phil Klotzbach told USA TODAY July 31. "The general consensus is that a temperature of 26.5°C (79 degrees F) is required to get a hurricane to form," he said.
University of Miami tropical researcher Brian McNoldy confirmed this, telling USA TODAY in an email August 1 that "looking at sea surface temperature, it's above the commonly-used 26°C isotherm everywhere of interest, so that ingredient is in place from Africa to the Caribbean to the Gulf."
So why no hurricanes?
So if ocean temperatures across the Atlantic are plenty toasty for hurricanes to form… what's preventing them from forming?
"One of the biggest disruptors of the Atlantic hurricane season so far has been unfavorable upper-level winds," Klotzbach told USA TODAY. "Atlantic vertical wind shear is generally westerly. We've had a lot of upper-level westerly winds over the past few weeks, increasing vertical wind shear across the Main Development Region."
Wind shear, a change in wind speed with height, is a hurricane killer, the National Weather Service said in an online report. "Strong upper level winds destroy the storms' structure by displacing the warm temperatures above the eye and limiting the vertical accent of air parcels. Hurricanes will not form when the upper level winds are too strong."
Shear might be diminishing, though
However, the upper-level wind anomalies are likely to flip to easterly in early August, resulting in reduced vertical wind shear and creating conditions much more favorable for Atlantic hurricane activity, Klotzbach said.
He said this flip is associated with an eastward-moving Madden-Julian Oscillation, a global climate pattern that affects hurricane formation.
"Phases 1-3 of the Madden-Julian Oscillation are the ones that are most favorable for Atlantic hurricane activity, and we should be headed into these phases shortly per the latest long-range forecast from the European Centre for Medium-Range Weather Forecasts," he said. "So, while things are quiet at the moment (and likely to remain quiet for the next few days), there are signs that things will pick up in about 10 days."
Hazelton agreed with this, noting that on X that "shear has already been coming down, and looks to drop even further as the Madden-Julian Oscillation moves over Africa. The Week 2 look on ensembles is about as favorable as you will ever see upper winds in the basin this time of year."
"Still, shear is just one part of the equation, and this time of year, moisture and stability can hold things back and prevent development even with low shear. Those issues seem prevalent already this year," Hazelton cautioned.
"It will be interesting to see how August goes tropical-cyclone-wise in the Atlantic."
This article originally appeared on USA TODAY: A key sign of hurricane activity heats up for August
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