Category: Posts EN

 

Blazing heat and high humidity are making for an explosive combination from the Plains all the way to the Eastern Seaboard. Extremely hot, unstable air is helping fuel dangerous wind storms in the western Great Lakes tonight. Meanwhile, residents of the big eastern urban centers are preparing for killer heat over the weekend.

 

 

A cluster of severe storms has been racing across parts of Minnesota and northern Wisconsin Friday evening (see animation above). The storms are feeding on abnormally high humidity and temperatures to the south and should continue to roll into Lower Michigan early Saturday morning. Reports indicate widespread winds of 60-80 mph (100-130 kph) have knocked down numerous trees and powerlines, resulting in thousands of power outages.

 

 

The same hot air mass has built into the Eastern Seaboard for the upcoming weekend. Temperatures from Washington D.C. through Philadelphia, New York City, and Boston will reach well into the 90s if not the lower 100s (upper 30s deg C). The record-threatening heat combined with high humidity will result in dangerous heat index values of 105 to 115 deg F. In this range, heat exhaustion is likely even with only short-duration outdoor activity. Prolonged exposure or physical activity outside can result in heat stroke, a potentially deadly condition. Heat-related illnesses account for more deaths annually than any other weather phenomena. This dangerous heat spell is made worse by the fact that overnight temperatures will not fall much, especially in the cities. That means very little opportunity for relief from the heat, increasing the risk of heat-related illness, especially among the elderly. Officials in all the major cities have opened hundreds of public cooling shelters and are encouraging those without access to air conditions to take advantage.

 

The first major heat wave of the summer is affecting the Plains and Midwest. By late this week into the weekend, the scorching hot air mass will spread east. Cities in the Urban Corridor will see heat index values well above 100 deg F!

 

 

A dome of strong high pressure has helped push air temperatures well above normal over much of the U.S. Meanwhile, a surge of tropical moisture originally tapped by now-extinct Hurricane Barry has encompassed much of the central and eastern states. This combination of hot temperatures and high humidity results in dangerous heat index values. Studies have shown that heat index values above 105 deg F greatly increase the risk of serious health impacts (see chart above). These include heat stroke, which can be fatal especially in the population of elderly and infirm. As you can see from the map below, this threshold will be passed over a large area of the central and eastern U.S. from Thursday through Sunday. Some areas will see peak heat index values of 115 deg F or higher! In urban areas like New York City, heat retained by the vast amount of asphalt and concrete will mean overnight temperatures staying warm. This is critically important as the human body requires recovery time between hot spells, especially those in vulnerable populations like the elderly. Indeed, extreme heat events are the deadliest among all weather events, killing more people annually than floods, tornadoes, or hurricanes.

 

 

Many areas have seen excessive heat warnings and advisories issued by the National Weather Service. More will be needed for the Thu-Sun time frame. Officials in some communities are going door-to-door to make sure vulnerable residents have supplies and shelter options as needed. Saturday looks to be the hottest day from the Mid-Atlantic to southern New England with some cooling likely beyond Sunday.

 

Hurricane Barry made landfall near Intracoastal City in south-central Louisiana around midday Saturday. Barry has continued to struggle with dry air intruding on the northern side. However, surface and reconnaissance plan data indicate the storm may have been producing hurricane-force conditions at landfall. As the storm moves further inland, heavy rain and flash flooding will become the predominant threat!

 

 

#Barry started the day not looking like a typical tropical cyclone.. now it does, ironically after moving inland pic.twitter.com/vde53o9FYv

— Stu Ostro (@StuOstro) July 13, 2019

Numerous reports of damaging winds and significant storm surge have been received from across southern Louisiana. Gusts of 40-70 mph (60-110 kph) have knocked down numerous trees and power lines, leading to thousands of power outages. A storm surge measured as high as 5-7 feet (2 m) has flooded coastal communities from the LA-MS state line to near the landfall point. Some levees protecting low-lying areas have been overtopped and damaged. Fortunately, as the center moves further inland, winds and surge flooding will continue to slowly subside, although localized flooding will still be likely around the astronomical high tide.

 

Terrebonne Parish in #Louisiana was hard-hit with storm surge inundation on Saturday. Here’s a few scenes from the area. #LAwx #Barry pic.twitter.com/a3Zrd8jThu

— WeatherNation (@WeatherNation) July 13, 2019

The heaviest rains so far have been falling to the south and east of the storm center. For much of the day, the heaviest rains were falling with a stationary band way east of the center, in Mobile, Alabama. Rainfall amounts up to 5-6 inches (125-150 mm) there lead to localized flooding. A new band of rain has set up over southeast Louisiana. This tropical moisture tap will be persistent through the next 24+ hours, eventually expanding further north into portions of Mississippi and Arkansas. Within this band, rainfall amounts of 3-6 inches (75-150 mm) will be common. Much heavier amounts of 6-12 inches (150-300 mm) or more are likely for central LA and southwest MS, where some serious flooding will occur.

 

Tropical Storm Barry remains somewhat organized with dry air disrupting the northern half of the circulation. Nevertheless, aircraft reconnaissance planes continue to find stronger and stronger winds in the core. Damaging winds, a significant storm surge, and especially torrential, flooding rainfall will accompany this dangerous storm!

 

 

The storm has been moving mainly to the west today, skirting just south of the coast (see satellite animation above). The track has shifted somewhat to the west in model guidance. Landfall is now expected to be closer to Vermillion Bay or Pecan Island. This is a fairly sparsely populated region, and the danger appears to be somewhat less in the New Orleans metro.

 

 

 

Barry remains a strong tropical storm as of Friday afternoon. However, it still has time to achieve hurricane status before landfall on Saturday. Regardless of whether it does or not, areas along the coast can expect to see high winds downing trees and power lines. The map above shows gusts already exceeding tropical storm force over southern Louisiana. A storm surge up to 5-6 feet in spots will also cause major problems along the central coast of Louisiana.

 

 

However, the most widespread danger will be from flooding rainfall. Although southern Louisiana has seen a relative break in the past 24 hours, a band of heavy rain is expected to become established over the southeast, especially west of New Orleans. This band will develop on Saturday and persist through Sunday and possibly into Monday. Within the band, totals exceeding a foot will be common, with some spots seeing closer to 24 inches! This copious rainfall will cause already-high rivers to rise even more, including the Mississippi, which is expected to reach the highest levels in nearly 70 years.