FORT LAUDERDALE, Fla. — Things are supposed to warm up in June, but not this much — especially the waters off the East Atlantic, where many hurricanes form.
Recent National Oceanic and Atmospheric Administration data shows that sea-surface temperatures globally are well above normal for this time of year — last month had the warmest May ocean temperatures since 1850, when record keeping began, registering 1.53 degrees higher than normal.
What matters most to Floridians is the water temperature off the west coast of Africa. The sea surface temperature there is as much as 3.5 degrees hotter than the norm. That energy can act as an accelerant to this summer’s hurricane season, sending hurricanes toward the U.S. earlier than expected.
When meteorologist and hurricane researcher Brian McNoldy, of the University of Miami, got a look at the data, he took to Twitter and wrote, “Tropical Atlantic water temperature is fast-forwarding by about 2.5 months. … The ocean is primed for action, already.”
Just how hot is the ocean? Globally, the mean June sea surface temperature between 1982 and 2011 hovered around 68.3 degrees. This year is 69.6.
In the North Atlantic, where hurricanes that affect Florida often form, the mid-June mean temperature between 1982 and 2011 was 71 degrees. This year the mid-June water temperatures are 73.1 degrees. On average, the region’s water doesn’t get that hot until after July Fourth.
McNoldy said the sharpest increase at the moment is in the far Eastern Atlantic, just off Africa, where, in the heart of hurricane season in August and September, we look for hurricanes to form. “That’s the part that’s really anomalously warm right now,” he said. “So it could give a bit of a kick-start to that part of the season.”
“It can have the effect of letting the deep tropical part of the [hurricane] season start sooner than normal,” McNoldy said. “Usually at this time of year, we don’t look to waves coming off of Africa for activity. We look to the Gulf of Mexico.”
“The sea-surface temperature can be a limitation for storms in the first part of the season. There are plenty of areas in the Atlantic that are not quite warm enough, usually, to sustain a hurricane. If you nudge those up by as much as they’re getting nudged up, all of a sudden those places are OK for hurricanes.”
There are other factors involved in hurricane formation, but he says, “having a warm ocean is the first step.”
Why is this happening?
Experts say the anomaly is too distinct to merely blame on climate change — there have to be other factors involved. But climate change has altered the baseline water temperatures by about 2 degrees since the early 1900s, so anomalies now become new records.
On top of the general climate shift, McNoldy said one major factor in June’s startling water temperatures off Africa is what’s called the Azores High, a big, semi-permanent subtropical high-pressure system that usually sits off the Azores, west of Spain. It has shifted significantly to the southwest.
Lately it’s been much weaker than normal, and about two weeks ago, it displaced to the southwest, closer to the Caribbean than to the Azores.
That has two effects that cause the eastern Atlantic to get hot. One, the east-to-west trade winds weaken, which allows the sea surface to be calm and heat more quickly.
Secondly, the plumes of Saharan dust that normally stream off Africa and across the tropics at this time of year dissipate. That allows more direct sunlight to heat the ocean. “That’s just not happening now,” says McNoldy. As a result, the waters off the horn of Africa’s west coast are thermally ahead of schedule.
The Gulf of Mexico is extremely hot right now as well. On June 9, ribbons of thousands of dead fish washed ashore southwest of Houston due to what officials said was a deadly combination of high water temperatures and windless conditions, resulting in low oxygen in the water.
Will the trend continue?
If the warming anomalies were to taper off as the summer continues it would relate to the Azores high returning to its normal position, McNoldy said. “We don’t know if these big anomalies will be in place in the heart of hurricane season.” It’s conceivable that temperatures could taper back to normal by the end of July.
“Will it be warming anomalously at the same rate? Probably not,” McNoldy said. “This is pretty extreme. The ocean can’t just keep getting hotter and hotter — it reaches disequilibrium with the air … there’s an air-sea exchange if the ocean gets too hot.”
Even if we get back down to normal, we’ll still have a warm peak season, says McNoldy.
The El Niño effect
The National Hurricane Center has called for a “normal” hurricane season with a likelihood of five to nine hurricanes this year, while factoring in both a warmer-than-normal Atlantic, and an El Niño weather system. An El Niño occurs when east-west trade winds over the Pacific Ocean weaken, allowing warm water to stack up off the west coast of South America. They happen every three to five years.
They also affect weather in the Atlantic, and can alter hurricanes. “All other things being equal, an El Niño can hinder Atlantic hurricanes through wind shear,” McNoldy said.
Wind shear occurs when winds at low altitudes are not blowing in the same speed or direction as winds at higher elevations.
McNoldy uses the analogy of standing a roll of paper towels on its end and pushing it across a table: “If you push the tube gently at the top and the bottom equally, it stays vertical and just slides across the table. Hurricanes like doing that.” But if you push the bottom and top at different angles or speeds, the tube will fall over. “A hurricane won’t fall over of course, but it will be very disrupted and will almost certainly weaken or even dissipate in extreme cases,” he said.
This season, though, all things are not equal, as seen with the hot East Atlantic.
“Hurricane Andrew happened in an El Niño year,” warned Jamie Rhome, of the National Hurricane Center, earlier this year. “El Niños are not going to stop hurricanes. El Niño may reduce total numbers, but it doesn’t stop them from coming to your community.”
