Heat in Delaware, July 4 to 6, 1999

A very strong and oppressive high pressure system that extended from the surface to aloft gave Delaware a brutal heat wave that included the entire Independence Day weekend. There were four heat related deaths, two in New Castle County, two in Sussex County. There were also about 10 heat related injuries reported. High temperatures reached the 90s for the first time on the 3rd, but sweltering humidity and record breaking maximum temperatures of around 100 degrees occurred from Independence Day through the 6th. The combination of the temperature and humidity produced heat indices of around 110 degrees during the afternoon of each day. A cold front moved through the region early in the morning on the 7th. While high temperatures continued to reach the 90s from the 7th through the 9th, humidity levels were lower. A stronger cold front moved through the region during the morning and afternoon of the 10th and brought in an even cooler and drier air mass. So after some places in central and southern Delaware had high temperatures in the 90s on the 10th, the run of 90 degree highs ended everywhere on the 11th.The heat related deaths occurred in Laurel (2) (Sussex County), Townsend (New Castle County) and Wilmington (New Castle County). In all instances the persons were found indoors without any air conditioning. One person's internal body temperature reached 108 degrees. About half of the reported heat related injuries occurred along the shore in Bethany Beach and Rehoboth Beach. Offshore winds kept the beaches as hot as inland locations. Several heat related injuries also occurred to the workers of the annual Wilmington fireworks display at Rockford Park. It was postponed after they became ill. The heat killed tens of thousands of chickens throughout the Delmarva Peninsula. One company alone lost 33,000 chickens. About twenty sections of highway in Kent and Sussex Counties experienced heat related buckling. Hardest hit was U.S. Route 113 with buckling in around a dozen places. The city of Wilmington distributed fans to the elderly to help them combat the heat. All summer school classes on the 6th were cancelled.The record heat led to record demand for electricity. Every local utility broke records. Conectiv Energy reported a record power usage of 3,418 megawatts within an hour on the 5th. The PJM Interconnection, a power pool that links electric utilities throughout the area churned out a record 52,000 megawatt hours of power on the 6th. The excessive demand for electricity strained electrical systems. Conectiv Energy instituted rolling blackouts to 40 percent of its 1.1 million customers in Maryland, Delaware and New Jersey at 1040 a.m. EDT on the 6th. A generator at Conectiv's Indian River Power Station failed. The blackouts affected 20,000 customers for 20 minutes at a time and included the city of Wilmington during the afternoon of the 6th. The Delaware Electric Co-Op also cycled off 15,000 air conditioning and water heater units to lighten the electrical load. Area wide, PJM reduced voltage by 5 percent at 2 p.m. EDT on the 6th to deal with the huge demand that was straining the electrical system. The highest temperatures during this hot spell occurred mainly on the 5th. They included 100 degrees in Georgetown (Sussex County), Milford (Kent County) and Salisbury (Wicomico County) MD, and 99 degrees at the New Castle County Airport. Many daily record high temperature records were either tied or set on the 5th and the 6th.