Heat Event Climatology in New Jersey

Prolonged episodes of extreme heat have a large impact on public health, utility services, transportation, infrastructure and more. This necessitates a climatological analysis of heat waves on a local scale, something that has become more common in recent years. The traditional definition of a heat wave is three or more consecutive days with maximum temperatures at or above 90 degrees Fahrenheit. This ignores climatological differences over a geographical area, as well as human ability to adjust to heat waves. Our analysis defined a “heat event” as three or more consecutive days of maximum temperatures being at or above the 90th percentile for each respective day. For example, if June 1, 2014, was in the top 10% for all June 1sts on record, we looked to see if June 2, 2014, was in the top 10% for all June 2sts on record, and so forth. We included results for the top 5% and 1% of data, along with events lasting five or more days. To make a more comprehensive heat wave analysis, minimum temperatures and diurnal temperature ranges were examined using the same methodology. Using data from eight reliable and long-term National Weather Service COOP stations, we were able to quantify extreme temperature trends over the May to September period for local areas of New Jersey. An initial analysis shows that over the period of record (approximately 100 years for each station), five out of eight stations have had an increase in prolonged heat events (five or more days at or above the 90% percentile). Additionally, seven out of eight stations have had an increase in warmer minimum temperatures (three more nights at or above the 90% percentile) over the period of record.