Weather service meteorologist Victor Murphy told The Associated Press that Texas' 86.8 average beat out Oklahoma's 85.2 degrees in 1934.
That Dust Bowl year is now third on the list for the three-month span, behind No. 2 Oklahoma's heat wave this June through August (86.5 degrees).
Both states and others in the nation's southern tier have baked in triple-digit heat this summer. Texas had its hottest June on record, the fifth warmest month overall, and July was the warmest month ever.
Oklahoma's July was the country's highest monthly average temperature ever, at 89.1 degrees.
Louisiana's heat this June through August puts it in the fourth spot all-time -- 84.5 degrees.
The average figures are taken from the entire 24-hour cycle of the day, not just from daily highs.
The reason for all the hot, dry weather lies thousands of miles away in the Pacific Ocean. The La Nina phenomenon is associated with cooler sea surface temperatures in the central and eastern tropical Pacific. It brings dry conditions to the southern U.S. states.
Unfortunately, the forecast shows the likelihood of La Nina re-emerging.
Texas hasn't just been hot this summer. It's in the midst of its worst drought since the 1950s and enduring its driest single year going back to 1895.
The heat and lack of rainfall have clobbered agriculture. An early estimate shows crop and livestock losses at $5.2 billion. That figure was expected to rise. The drought and scorching temperatures have burned grazing pasture and rangeland, forcing ranchers to severely cull herds. Ranchers keeping animals are paying high prices for supplemental feed or the cost of transporting their animals to states with grazing land.
Producers who planted more than 2 million acres of cotton that rely on only rainfall to grow in the world's largest contiguous growing patch around Lubbock abandoned their fields.
Texas' economy will take a more direct hit. Agriculture accounted for $99.1 billion of Texas' $1.1 trillion economy, or 8.6 percent, in 2007, the most recent year data on food and fiber was available from the extension service. Losses in that sector have a ripple effect that's about twice the amount of the actual agricultural loss.
Grasses, vegetation and trees around the state remain tinderbox dry and wildfires have destroyed more than 3.5 million acres since last November, about when the drought started. Just this week, hundreds of homes were destroyed when wildfires raged southeast of Austin.
Fish and other wildlife are struggling as lakes and rivers are drying up across the state and more than 850 water suppliers have implemented mandatory and voluntary restrictions on usage. Two Central Texas springs relied upon for life by eight endangered and threatened species are perilously close to levels that will require an evacuation by federal wildlife officials.
The U.S. Drought Monitor map released Thursday shows that not a speck of Texas is out of drought, and more than 81 percent is in the worst category. A year ago just 15 percent of Texas was abnormally dry, the least dry status on the map.
Other states in the southern U.S. also are in drought. Almost all of Arizona and Oklahoma are in some drought stage. All of New Mexico is mired in drought, with about 38 percent of it in the worst stage -- exceptional. About 70 percent of Oklahoma is in exceptional drought.