The arrival of summer will be marked by a period of intense heat across the Eastern U.S., with widespread record-breaking temperatures expected across the Ohio Valley and Northeast.

The first long-duration heat wave is already underway across the eastern U.S., with temperatures potentially reaching the triple digits in the Ohio Valley and Northeast through mid-week. This potentially historic heat wave could break daily high-temperature records dating back to the 1920s in places like Boston, where Wednesday's maximum temperature might reach the upper 90s.

While the northeastern quadrant of the U.S. bakes, the Mid-South region will see some relief from the heat as deep tropical moisture brings showers and thunderstorms northward across eastern Texas and the Lower Mississippi Valley. Some of these storms could produce significant rainfall totals, increasing the risk of flash floods, especially along coastal areas, including cities like New Orleans, Mobile, and Houston.

In addition, a second area of concern for strong to severe storms today will be across the Northern Plains, affecting parts of the Dakotas and Minnesota. The primary threats from these storms will be large hail and strong wind gusts.

The main area of concern is in the southern Gulf of Mexico, where an envelope of deep tropical moisture associated with a broad low-pressure system is producing showers and thunderstorms. This system is forecast to meander mostly in place or move slightly north. If it takes a more northward track, the risk of flash flooding will increase across southeastern Texas.

Now that we're in the longest days of the year, we know you have plenty of outdoor activities planned. We're here to support that! We've added length-of-day information to the Astro info card on all iOS devices. And don't worry Android users, this feature is coming to you soon, too.