We're at the peak of Atlantic hurricane season. What's next?

September 10 is the climatological peak of hurricane season in the Atlantic Ocean. This is the day with the greatest odds of having at least one named storm somewhere in the Atlantic basin—and, true to form, we've got a hurricane brewing in the Gulf of Mexico.

It's clear that this year isn't going to live up to expectations of a hyperactive hurricane season. But that doesn't mean we should let our guard down. Here's what we could expect from the second half of hurricane season ahead.

All signs pointed toward a bustling basin

The field's leading experts almost unanimously called for an extremely active hurricane season this year.

An average Atlantic hurricane season would see 14 named storms, seven of which would strengthen into hurricanes, and three of those turning into major hurricanes. NOAA called for 17-25 named storms this season, while the good folks over at Colorado State University expected about 23 named storms this year. 

Why so bullish? Everything seemed to be aligning just right. We're in between El Niño and La Niña right now. An active monsoon season across sub-Saharan Africa should've led to more disturbances that could seed the development of tropical systems.

On top of all that, sea surface temperatures across the Atlantic have been near historic highs for over a year now. Those sultry ocean waters helped power an above-normal hurricane season last year despite the odds against it. 

Things haven't panned out as expected

The atmosphere is complicated. Meteorology, for all its incredible advances over the years, is still an inexact science. There's plenty that even the leading minds in the field are still working to understand about the intricate links between every aspect of our skies above.

Despite all the ingredients seemingly coming together for a blockbuster hurricane season, it's been...well, not that. Hurricane Beryl showed us what those hot sea surface temperatures are capable of when it roared into a category five storm in early July. Since then, though, we've only seen a smattering of named storms.

Francine, which is gathering strength in the Gulf as of this post, is only the season's sixth named storm. If projections remained on track, we should've seen twice as many storms form by the peak of the season.

Lots of factors contributed to this unexpected lull in hurricane activity. I wrote a bit about it for The Weather Network a couple of weeks ago:

[...] You can’t bake a sweet cake with just flour. Water temperatures are just one part of the equation that plays into the formation of a vigorous tropical cyclone. This precise mix of ingredients includes moist air, calm wind shear, and vigorous thunderstorms that serve as the seed from which a hurricane grows.

Those ingredients have been a little bit out of step this season. Monsoon rains in sub-Saharan Africa have been travelling farther north than usual—bringing rare rains to the desert while missing key windows to seed tropical disturbances over the Atlantic. We've also seen intrusions of dry, dusty air puffing off the desert itself, as well as a general lack of instability over the tropical Atlantic.

The dangers of a "quiet" season

If you follow any meteorologists on social media, you've probably seen a lot of this introspective chatter over the past week. But Francine highlights the danger of banging away at this being a supposedly quiet season: it only takes one storm to make a mess.

An example I frequently use is the 1992 hurricane season. That was a below-normal hurricane season that didn't produce its first named storm until the end of August. That storm was Hurricane Andrew. That's not to say we're going to see anything close to a repeat. But this season has already proven what it's capable of in Hurricane Beryl's rapid intensification over the Caribbean.

Storms toward the latter half of hurricane season tend to form closer to land, reducing the amount of time residents have to react and prepare for a storm's arrival. Look at Francine in the Gulf—if anyone in Louisiana tuned out the weather over the weekend, they were probably shocked by the hurricane warning that hit their phone last night.

Folks throughout the southern and eastern United States need to remain prepared for dangerous storms well into November. Even though this season isn't going as expected, we've got a long way to go before the basin shuts down for the winter. September and October have a long history of nasty storms swirling ashore. 

Make plans to deal with dangerous weather, including potential evacuations, flooding from heavy rainfall, and even tornadoes as storms push inland. Make sure you've got an emergency kit ready for power outages that could last days—even far inland from where a storm might make landfall.

[Satellite image of Beryl courtesy of RAMMB/CIRA]

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Francine expected to hit the northern Gulf Coast as a hurricane Wednesday

A dangerous storm developing in the southwestern Gulf of Mexico will make landfall as a hurricane Wednesday along the Louisiana coast.

Tropical Storm Francine spent Monday rapidly getting its act together off the eastern shores of Mexico.

The latest advisory from the National Hurricane Center (NHC) says that Francine has maximum sustained winds of 65 mph. The storm even appears to be developing an eye based on satellite and radar imagery, which is a sign the storm could soon close in on hurricane intensity.

Sea surface temperatures are a few degrees warmer than normal across the western Gulf, partially a result of having next to no storm activity over the region so far this year. (Tropical systems churn up cooler waters from below, even if briefly.)

Given the warm ocean temperatures and favorable environmental conditions around the storm, forecasters expect Francine to strengthen into a hurricane before making landfall on the central Louisiana coast during the day Wednesday.

Wind and Storm Surge

The NHC expects Francine to be near peak strength by the time it makes landfall in Louisiana on Wednesday. 

Widespread tree damage and long-lasting power outages are possible where Francine's eyewall makes landfall. Hopefully the worst winds remain over the relatively unpopulated bayous, but Lafayette—home to more than 100,000 people—could find itself in or close to the eyewall based on the current projected track.

Damaging winds are possible as far east as New Orleans and as far west as Beaumont, Texas. The outer edges of the storm could bring winds high enough to cause some downed trees and sporadic power outages.

A life-threatening storm surge is likely along the coast where Francine makes landfall. The latest advisory calls for a storm surge of 5-10 feet where the eye crosses the coastline if landfall coincides with high tide. This is some of the most surge-vulnerable land in the United States. Storm surge flooding can extend many miles inland across southern Louisiana's flat, marshy terrain. 

Any eastward jog in the storm could bring more dangerous wind and storm surge closer to New Orleans.

Heavy Rainfall

Tropical downpours are a certainty along Francine's track inland. The majority of deaths associated with landfalling tropical storms are the result of flash flooding from heavy rainfall. 

The Weather Prediction Center calls for 5-7+ inches of rain along Francine's track inland, which will pretty closely follow the Mississippi River north of Baton Rouge. Several inches of rain could fall as far west as Little Rock and as far east as Birmingham through the end of the week.

It's also worth noting that little bullseye over upstate South Carolina and adjacent areas. Southerly winds and enhanced moisture associated with Francine flowing up the foothills could produce 3-5 inches of rain over the region, leading to a localized flash flood threat. 

Almost all flash flood injuries and deaths are preventable. Never drive across a flooded roadway. It's impossible to tell how deep the water is until you're in it, and the road itself could be washed out beneath the water. It's not worth the risk to your life or those who have to rescue you or recover your body.

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Hot and humid nights drove another summer of record heat across the U.S.

This was one of the hottest summers—if not the hottest summer—ever recorded for large portions of the United States, another data point on the undeniable trend toward warmer days and even warmer nights as our climate steadily changes.

Meteorological summer began on June 1 and ended on August 31. This clean division of months more closely tracks temperatures than dividing the year up based on astronomical solstices and equinoxes.

The overall pattern we saw this summer featured persistent ridges of high pressure over the western and eastern ends of the U.S., with troughing in the center of the country.

Ridges foster sinking air, which warms up as it compresses on descent toward the ground. Troughs force air to rise, leading to unsettled weather and generally below-seasonal temperatures.

Source: IEM

We can see this divide in a map showing how much average daily temperatures departed from normal. A day's average temperature is the daytime high and nighttime low averaged together. Troughing in the center of the country led to somewhat seasonable temperatures, while folks west of the Rockies and east of the Appalachians dealt with warmer-than-normal conditions.

What really stands out is the desert southwest.

Folks in Phoenix, Arizona, just lived through their hottest summer on record. The daily average temperature there was a whopping 98.9°F this summer, which beat the previous record (set last year!) by nearly two degrees.

This summer's daytime highs in Phoenix were absolutely blazing hot—as of this post, the city is in the midst of a 100-day streak of daytime highs at 100°F or hotter, exceeding the previous record 100-degree streak by nearly three weeks.

Source: IEM

But it was the nighttime lows that really stood out.

Every single day this summer saw a warmer-than-normal low temperature, with those departures often coming in 10 or more degrees above normal. That's no small thing when midsummer nights don't cool off much in the desert. The city's low temperature in July only dipped below 88°F five times, and it remained 90°F or warmer at night 19 days throughout the month.

Here are the Summer (Jun-Aug) 2024 A) temperature rank, B) temperature departure from normal, C) precipitation rank, and D) precipitation percentage of normal. pic.twitter.com/8lUdLBQ1j7

— Brian Brettschneider (@Climatologist49) September 2, 2024

While not as unbelievably hot, the story of nighttime lows driving near-record summertime temperatures is constant up and down the East Coast.

Take a look at interior New England, where Caribou, Maine, just saw its warmest summer since records began there back in 1939. Repeated intrusions of muggy air in late June, mid-July, and in early August made low temperatures above 65°F a common sight in this small community near the Canadian border. For reference, Caribou's average low on July 16—summer's midpoint—is about 57°F.

This summer's noteworthy heat and humidity follows the pattern you'd expect to see as the climate changes.

Source: Climate Central

As I wrote back in July: "Climate change sets a new baseline for extreme heat throughout the United States and around the world. As the entire frame of reference moves toward a hotter climate, warm temperature extremes are far more likely that cold temperature extremes. Excessive heat will come in hotter than what we grew used to just one or two generations ago."

A warmer atmosphere can also hold more moisture. This increase in humidity makes it harder for nights to cool off as much as they used to, which is a significant factor driving warmer-than-normal summer low temperatures.

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