Thunderstorms and soaring temperatures could interfere with Labor Day weekend activities across the nation, as an anticipated large number of travelers hit the roads and skies for the unwritten end of summer.

From Friday through Monday, many areas will experience heavy rain and potential flooding, particularly in the Midwest, Plains, Mid-Atlantic, and Gulf Coast regions. At the same time, parts of the Northwest are bracing for a significant heat surge, with temperatures expected to soar 10-20 degrees above normal for this time of year.

Beyond the mainland U.S., remnants of the former tropical storm Gilma are forecasted to bring substantial rain and strong winds to Hawaii over the weekend. Additionally, new tropical systems in the Atlantic may introduce showers and thunderstorms to the U.S. Virgin Islands and Puerto Rico around Labor Day and into the following week.

However, poor weather isn’t the sole challenge for a pleasant holiday. Rising bacteria levels and algae concerns led to the closure of various beaches nationwide, including over 60 in Massachusetts alone.

The Transportation Security Administration expects that over 17 million travelers will pass through airport checkpoints between Thursday, August 29, and Wednesday, September 4, likely making this the busiest Labor Day travel period ever recorded.

Here’s what to keep in mind about the holiday weekend’s weather forecast:

Storm activity expected to impact central and eastern U.S. at weekend’s start

On Friday, a large area spanning the central and eastern U.S. may encounter thunderstorms, reaching from New Mexico, Texas, and Louisiana up to Michigan, western New York, central Pennsylvania, and across the Florida Peninsula, according to AccuWeather.

This expansive area of concern covers 20 states; while the precipitation may not be constant, it still presents a risk of “potentially severe conditions,” as per AccuWeather’s assessment. Storms anticipated over the lower Great Lakes and Mississippi Valley could generate “thunderstorms and heavy rainfall, with chances of isolated flash flooding” as described by the weather service.

A secondary trough may lead to increased wind gusts in the Great Lakes region, establishing a risk level of 2 out of 5 for damaging winds in eastern Michigan determined by the Storm Prediction Center.

Northeast faces intermittent rain and flood risks

The potential for severe storms extends further into the Ohio Valley and Northeast on Saturday and Sunday, with “areas of severe weather” forecast to impact the Appalachians and Mid-Atlantic regions, according to the weather service.

Major cities at risk include Philadelphia, Baltimore, Washington D.C., Pittsburgh, and Arlington, as identified by the Storm Prediction Center.

“Damaging winds will again be the main concern,” the weather service indicated. “Moreover, isolated flash flooding remains a possibility, with the chance of increased risk due to the slowing movement of the front.”

A cold front sweeping through the Midwest and Plains should bring relief from the extreme heat experienced in parts of the Mid-Atlantic this week, especially in Washington D.C., where the temperature hit a record high of 101 degrees on Wednesday, exceeding the previous record of 99 degrees set in 1948, according to the Capital Weather Gang.

Gulf Coast states preparing for thunderstorms

While certain areas of the Southeast may stay mostly dry over the weekend, the Gulf Coast and surrounding regions might be affected by heavy rain.

This weekend, forecasts indicate that heavy rainfall will target parts of western Louisiana and the upper Texas Gulf Coast due to a lingering low-pressure system. Increased rainfall rates along with repeated storm activity could result in “scattered flash flooding,” as per the weather service. Daily thunderstorms are also anticipated across central and southern Florida.

Heavy rain is expected on Labor Day stretching from Texas to the Carolinas, Georgia, and Florida, where localized flash flooding may occur, as stated by AccuWeather.

Many Massachusetts beaches closed due to bacterial concerns

Over 60 beaches in Massachusetts are closed due to high bacteria levels and other dangers, such as toxic chemicals and rip currents.

The Massachusetts Department of Public Health (MDPH) warned in a statement that swimming in the water at these closed beaches poses a risk of illness due to elevated bacteria levels. Symptoms could include nausea, vomiting, sore throat, and fever.

This year, the number of beaches closed has significantly decreased compared to last year when over 90 beaches along the state’s Atlantic coast were shut down.

Elsewhere, officials advised beachgoers to stay away from certain areas due to bacterial issues. In Michigan, warnings were issued for five beaches because of “high bacteria levels from an unknown source.” Meanwhile, in Wisconsin, four beaches in the city of Lake Geneva remained closed due to the presence of blue-green algae, which can produce toxins harmful to both humans and animals, potentially leading to severe illness or even death in extreme cases.

In Florida, a health alert was issued by the Duval County Health Department regarding toxic blue-green algae found in the St. Johns River, the longest river in Florida. This algae bloom is linked to the accumulation of excessive nutrients in the river, primarily nitrogen.

Northwest to experience extreme heat over Labor Day weekend

A late summer heat wave has prompted advisories throughout the Pacific Northwest, with forecasters predicting temperatures to rise significantly above seasonal averages over the holiday weekend.

According to AccuWeather, temperatures in the Basin and Pacific Northwest are expected to reach their highest point in the mid-90s. On Saturday, the heat will intensify as it moves into the northern Rockies, pushing temperatures into the upper 90s.

The weather service office in Spokane, Washington, has issued a heat advisory that will start Saturday morning and last until Monday night. Forecasters predict “hot conditions with temperatures ranging from 95 to 100 degrees” across central and northeast Oregon and southeast Washington, as reported by the Pendleton, Oregon weather service.

“Warnings have been issued for much of the northern Great Basin due to an increased risk of heat-related illnesses, so individuals are advised to seek shade and ensure they stay hydrated during this holiday weekend,” the weather service cautioned.

Contributors: Kathleen Wong, YSL News; Catherine Messier, The Patriot Ledger; Cheryl McCloud, YSL News Network-Florida; Claire Reid, Milwaukee Journal Sentinel