A massive dome of high pressure is splitting the United States between record-challenging heat and unusually cool weather, while a narrow battleground between the two is producing thunderstorms, heavy rain and a continued flash-flood threat, according to meteorologist Jonathan Kegges.
Kegges, host of the JustWeather YouTube channel, described the setup as a classic “ring of fire” pattern, with high pressure anchored across the South and Southeast while cooler air settles farther west and north. Along the outer edge of the heat dome, moisture and storm systems are being steered around the ridge, creating repeated chances for downpours and stronger thunderstorms.
He is also watching a separate development farther down the road, saying the same large-scale pattern may eventually help determine where any tropical system that forms in the Gulf later this month could travel.
Heat Dome Keeps The South Very Hot
Kegges said the basic setup heading through the end of the workweek features a large ridge of high pressure centered across the Southeast, where temperatures remain unusually high for the middle of September.
Cities including Oklahoma City, Little Rock, Nashville and Roanoke could challenge records, with some locations climbing well into the 90s.
Farther west, however, a trough of low pressure is allowing much cooler air to settle into parts of the country.
Kegges highlighted below-normal temperatures around places such as Boise, Eugene and portions of California, while Minneapolis was expected to remain much cooler than the southern Plains and Deep South.
That sharp contrast is what makes the pattern so interesting. One part of the country is still locked in something that feels like midsummer, while other areas are already getting a noticeable taste of fall.
Between those two air masses is where the atmosphere becomes much more active.
Storms Ride Around The Edge Of The Ridge
Kegges explained that the “ring of fire” nickname comes from the way storms tend to develop around the outside of a large high-pressure system rather than directly underneath it.
High pressure promotes sinking air in its center, which usually suppresses widespread thunderstorm development.
Along its edges, however, winds can pull in moisture and provide a pathway for disturbances to move around the ridge.
Kegges said that is happening from the Southwest into the Midwest, Great Lakes and Northeast, while another stream of moisture is reaching parts of Texas and Florida.
The storms are essentially tracing the outer edge of the heat dome.
That means the same high-pressure system responsible for widespread heat is also helping organize where the rain and thunderstorms form.
Flash Flooding Remains A Concern
The Desert Southwest remains one of the areas Kegges is watching most closely for flooding.
He said repeated surges of Pacific moisture could continue feeding thunderstorms across the region, where heavy rain can quickly create problems because dry ground and steep terrain do not always absorb water efficiently.
Training thunderstorms are an especially important concern.
Those occur when storms repeatedly move across the same location, allowing rainfall totals to build quickly even if any one storm is not particularly long-lived.
Kegges also mentioned the possibility of backbuilding storms, where new thunderstorms repeatedly develop along the same boundary and keep feeding rain into an area that has already been soaked.
The monsoon has been uneven this year, he said, with some locations receiving substantial rainfall while others have missed out, but the broader flash-flood threat remains in place.
Midwest And Northeast Stay In The Active Zone
Farther east, the northern edge of the high-pressure system will keep an active storm track in place from portions of the Midwest into the Great Lakes, Ohio Valley and Northeast.
Kegges said scattered downpours and thunderstorms are possible across areas including Ohio, Pennsylvania and New England as disturbances continue riding over the top of the ridge.
Another cluster of storms is expected to move near the Twin Cities before progressing toward Wisconsin and Michigan.
The pattern may repeat itself as daytime heating helps storms redevelop.
Texas could also get some needed rain, particularly closer to the coast, where Gulf moisture is expected to help spark thunderstorms.
Kegges showed how the clockwise circulation around the surface high-pressure system can pull moisture inland from different directions, with Pacific moisture feeding storms in the Southwest while Gulf and Atlantic moisture reach the southern and eastern sides of the ridge.
It is a good example of how one large atmospheric feature can affect weather thousands of miles apart in very different ways.
Tropical Signal In The Gulf Is Growing
The longer-range part of Kegges’ forecast focused on the Gulf of Mexico, where he said a signal for possible tropical development is becoming more interesting toward the final week of September and potentially the first week of October.
He repeatedly stressed that there is no storm to track yet.
“There’s nothing concrete,” Kegges said, cautioning viewers against treating any single long-range model image as a forecast.
His interest comes from the fact that multiple ensemble models are beginning to show some level of tropical development in the region, while the larger atmospheric background is also becoming more favorable.
That combination is what separates the current signal from what Kegges described as a “phantom” storm shown by one model earlier in the month.
Rather than focusing on one dramatic computer run, he said the more important question is whether there is an actual atmospheric reason for tropical activity to become more likely.
In this case, he believes there is.
MJO Could Make The Gulf More Favorable
Kegges pointed to the Madden-Julian Oscillation, or MJO, as one of the main reasons he is paying attention.
He described the MJO as a pulse of enhanced and suppressed thunderstorm activity that travels around the globe every 30 to 60 days.
For much of the hurricane season, Kegges said the more favorable part of that pattern has remained over the Pacific rather than moving into the Atlantic basin.
That may begin changing late in September.
Forecast guidance shows stronger rising motion moving into Central America, the western Caribbean and Gulf region around the final days of the month, with some of that favorable environment potentially continuing into early October.
Kegges said the period may become “the best the basin will look all season” from a large-scale standpoint.
That does not guarantee a tropical storm or hurricane will form.
Dry air, wind shear or other hostile conditions could still prevent development, and Kegges emphasized that specific tracks or intensities are impossible to forecast this far in advance.
Still, several model systems are showing enough activity that he believes the Gulf is worth monitoring.
Late September Bears Watching
Kegges said the timing also matches climatology.
As September turns into October, tropical development often becomes more focused in the western Caribbean and Gulf rather than the far eastern Atlantic.
That makes the emerging signal more believable than a model suddenly creating a storm in an environment that does not support one.
For now, he said the correct approach is simply to watch.
The immediate weather story remains the large heat dome splitting the country, with record heat underneath it, cool weather on the opposite side and storms wrapping around the edges.
But the same steering pattern could become much more important if tropical development eventually emerges in the Gulf.
Kegges made clear that it is far too early for alarm, but the ingredients are beginning to line up enough that the final week of September deserves attention.
Until then, the “ring of fire” will remain the dominant feature, separating summerlike heat from early fall air while keeping a busy corridor of thunderstorms and flooding threats between them.
Mark grew up in the heart of Texas, where tornadoes and extreme weather were a part of life. His early experiences sparked a fascination with emergency preparedness and homesteading. A father of three, Mark is dedicated to teaching families how to be self-sufficient, with a focus on food storage, DIY projects, and energy independence. His writing empowers everyday people to take small steps toward greater self-reliance without feeling overwhelmed.
