Mark Schleifstein | 25 June 2022

The record June heat wave in southern Louisiana, with water temperatures edging into the mid-90s on Friday in Lake Pontchartrain and along the Gulf Coast, is serving up a triple whammy of water-related dangers: an elevated risk of intense hurricanes, an increased number of dangerous Vibrio bacteria infections, and more fish kills.

As air temperatures bubbled into above-100 realms on Friday in some locations, the Slidell office of the National Weather Service reported that the average temperature of 88.1 degrees for the seven days ending Thursday marked the hottest June week on record. It beat a previous record in 2012 and marked the 17th-warmest seven days for any time of the year.

And forecasters warned those seven-day records were likely to fall after Friday and Saturday temperatures were measured.

What could be even more problematical for businesses and residents forced to keep air conditioning running at maximum levels overnight is that daily low temperatures for the two weeks ending Thursday also marked the warmest two-week stretch for June on record, at 78.1 degrees. And Weather Service meteorologist Jared Klein pointed out that the high in New Orleans has reached at least 95 for nine days in a row, tied for the 5th-longest stretch of 95-degree days on record.

“The latest forecast supports this streak to extend to 11 straight days after the weekend, which would place it in a tie for the 3rd-longest,” he said in a Friday forecast discussion message.

And the increased temperatures this year are part of a pattern stretching back more than 50 years in New Orleans, according to Climate Central, an independent group of scientists and communicators who research and report on climate change. Their review of records indicate the average summer temperature in New Orleans has increased by 1.5 degrees during that time.

Those high temperatures are definitely affecting local water bodies, officials say, and the most significant threat could be along the Gulf Coast, where surface water temperatures have reached at least 88 degrees, “which is significantly higher than usual,” said Matthieu Le Henaff, a researcher with the University of Miami and NOAA’s Atlantic Oceanographic Meteorological Laboratory.

Water temperatures along Louisiana’s coast in June during the past few years have often been at least a few degrees lower because of flood-swelled flows from the Mississippi and Atchafalaya rivers, often cooled by snowmelt from the Midwest. But this year, water levels have dropped well below those past flood levels.

And Louisiana’s warmer than normal coastal waters are problematical for another reason this year, says Nick Shay, a marine researcher with the University of Miami’s Rosenstiel School of Marine and Atmospheric Sciences.

Shay points out that the southernmost segment of the Gulf Stream – a deep current of much warmer water that stretches from the Caribbean Sea through the Yucatan Straits into the southern Gulf before looping around the eastern coast of Florida – has bowed well north into the northeastern Gulf without breaking off into a separate deep, warm water eddy.

Water at the surface of that current is running around 82 and 84 degrees, about the same as the Gulf waters surrounding it, Le Henaff said. But while those warm temperatures are only at the surface in most of the Gulf, in the loop, those much warmer temperatures extend to 3,000 feet below the surface.

If a tropical storm or hurricane’s path cuts across even part of that deep, warm water, it could cause the storm to rapidly intensify, jumping one or two categories in strength in just a few hours.

In most of the Gulf, as a hurricane passes over warm water, its forces pull cooler water up from the depths, and the storm is more likely to weaken. Over the loop current, the deep warm water acts as if someone’s turning up the gas burner on a stove, Shay said.

The warmer water along Louisiana’s coast also reduces the chance of weakening, he said.

At the moment, some of that increased risk is being tempered by dry air in the upper atmosphere, a wind current called the Saharan Air Layer that’s been delivering dust from the Sahara Desert to Louisiana and Texas for the last few weeks.

“Storms don’t like dry air,” he said, but added that it’s becoming clear that the dry air and its dust are likely to end in the next few weeks, increasing the chance of tropical storms in the Gulf.

The warmer, brackish water along Louisiana’s beaches and estuaries also poses a health problem for those vulnerable to bacterial infections, the Louisiana Department of Health warns.

State officials report that they’ve already received 47 reports of Vibrio illnesses, including some linked to Vibrio vulnificus, a bacteria that can cause an illness called vibriosis if ingested in raw seafood, particularly oysters, or if it enters open wounds in salty or brackish water.

The open wound infections can result in amputations or death.

“The number that have been reported at this point are consistent with what we have seen in previous years. However, we do typically see an increase in cases during warm weather months, and such is occurring this year,” said department spokesman Kevin Litten.

The department also has received reports of only a few minor cases of algae blooms in Lake Pontchartrain and other water basins, according to the health department and to Brady Skaggs, water quality program director at the Pontchartrain Conservancy.

Skaggs said it’s too soon to declare June a record-setting year for water temperatures in Lake Pontchartrain.

At the moment, the record identified by the Conservancy’s collection of daily and weekly water temperatures in the lake dating back nearly 30 years is 97.3, measured at Bayou St. John on July 26, 2012. That compares to an hourly high of 93 measured by the U.S. Geological Survey at the New Basin Canal at 6 p.m. Thursday, and a weekly average high of 90.7 measured by the Pontchartrain Conservancy at Pontchartrain Beach in New Orleans.

Temperatures have actually been higher in other area lakes and bayous this June, with the USGS recording a temperature of 96 in Bayou Perot near Cutoff at 6:30 p.m. on Wednesday, and 94.3 in Lake Cataouatche near Waggaman at 6 p.m. on June 16.

The high water temperatures, combined with clear skies resulting from lengthy periods of high pressure over the state and Gulf that have suppressed thunderstorms, make conditions ripe for the loss of oxygen in the lake and stream water. Higher temperatures mean oxygen is less likely to dissolve into the water, and the high pressure keeps storms from mixing oxygen-rich surface water into lower levels.

The oxygen is needed for survival by many fish species and bottom-living organisms like oysters and mollusks, said Robby Maxwell, a biologist supervisor with the Louisiana Department of Wildlife & Fisheries.

“We’re getting fish kill reports, the majority from neighborhood ponds and often after a pop-up thunderstorm hits,” he said, which churns the low-oxygen water on lake bottoms and mixes it with rotting debris. This year’s prolonged drought is exacerbating problems for those small water bodies.

According to the National Weather Service, most of southeast Louisiana has received no more than an inch and a half of rain over the past week, with rainfall deficits in some areas reaching six inches for the year.

The result is extreme drought conditions south of a line from Houma to Empire and severe drought below a line from Thibodaux to Lafitte to Delacroix, with moderate drought conditions in the rest of the region.

The present conditions are not unexpected, Maxwell said.

“We’ve come off a really wet stretch during the past 10 years,” he said.

The most likely fish killed have been shad and menhaden, or pogies, which are extremely sensitive to low oxygen. Other fish are more resilient, with some species being able to gulp air at the surface, he said. He recommends private pond owners try using aerators or diffusers, or even water pumps to mix in oxygen, if possible.

But he also said the dead fish are not really a worry for the long-term health of local species.

“It’s the reason they have tens or hundreds of thousands of babies,” Maxwell said. “After a fish kill, there’s also a lot less competition, predation, so repopulation usually happens quickly.”

The warmer water along the state’s coast also is expected to impact the size of this year’s low-oxygen dead zone in the Gulf, said Nancy Rabalais, a Louisiana State University marine biologist.

She said the warmer and calmer waters along the coast support the growth of more phytoplankton, the algae that feed on nitrogen, phosphorus and silicon, that eventually die and sink to the bottom, where bacteria eat them, using up oxygen.

Bottom-living organisms that can’t travel are killed, and crabs, shrimp and fish attempt to escape to areas with more oxygen.

In some cases, some of the blooms may contain toxic cyanobacteria that can cause “red tides” that also are linked to fish kills.

Rabalais said the production of carbon dioxide during the low-oxygen period also can help cause ocean acidification, which also has been linked to survival problems with shellfish.

This year, NOAA has predicted that the area of very low oxygen could be as big as the state of Connecticut.