For much of the U.S., May brought a break from the string of months that have been much warmer than normal and even the warmest on record in many instances. But a heat wave set to sweep across the country will soon turn up temperatures again.

Averaged nationwide, U.S. temperatures were very close to normal in May, although there were a few exceptions. Washington, which was one of the few states that had been consistently cooler than normal so far in 2017, turned the corner, along with the rest of the West Coast, and was warmer than normal in May.

may temperatures

May temperatures in the United States.

Only three states east of the Mississippi were warmer than normal in May: North Carolina, South Carolina, and Florida. The Sunshine State has been in the grips of a spring drought, which is generally an indicator of more sunshine, likely contributing to the warmth. But the wet season is starting to kick in there, and much of the state received beneficial, if not flooding, rain earlier this week.

May was wet for much of the Midwest and the East, helping those locations ease away from the hot streak. Several states in the Middle Atlantic and the Northeast had one of their 10 wettest Mays on record. The additional cloud cover that comes with the rainy days helped keep daytime temperatures down.

But the same clouds that reflect incoming solar energy during the day also work to insulate the ground at night, keeping temperatures up. As a result, all of the East Coast states had low temperatures for the month that were above normal. Despite high temperatures being below normal from Virginia to the Northeast, the warmer nights compensated, so the overall temperatures were actually close to normal.

2017 temperatures

January-May temperatures in the United States.

But like a single bad inning in a baseball game filled with hits, May was a hiccup in the ongoing string of warm months for the U.S., as warming from the increase in greenhouse gases continues to drive temperatures up over the long term. Nationwide, it was the eighth warmest spring (March, April, and May) on record. And even with the relatively cooler May, this year is the second warmest on record for the U.S. through the end of May. Texas, Florida, Georgia, and both Carolinas are all having their hottest year on record so far.

But the relatively cool weather in the East has ended. A recurring southerly dip in the jet stream in the eastern U.S. had help keep most of the searing heat at bay, but that dip has effectively migrated to the West for the next few days. Afterwards, the jet will retreat northward toward Canada, which is a more typical position for this time of year. As a result, heat will flood the eastern U.S. for for the end of the weekend and the beginning of next week, with highs in the 90s as far north as New England.

The outlook for the rest of the month from the National Oceanic and Atmospheric Administration’s Climate Prediction Center suggests the heat holds for the East Coast and builds once again for the West Coast. Even if the shorts and swimsuits have not gotten much use yet, their time has arrived.