A Warm & Dry End to Summer: August 2015

 

August started off hot with temperatures reaching the upper 80s to low 90s for the first four days of the month. By the 4th, severe weather broke out as a cold front traversed the Northeast with New England especially hard hit. In fact, a supercell or rotating thunderstorm pummeled through Massachusetts, producing 50 - 60mph wind gusts and golf ball sized hail stones.

 

Canadian high pressure took control during the following days, alleviating the Northeast from the heat and keeping the region mainly dry. While a system tried pushing north out of the Mid Atlantic on the 7th, high pressure suppressed showers to southern New Jersey and the Delmarva, further exasperating ongoing rain deficits. Luckily, a warm front on August 11th ushered widespread rain into the Northeast with embedded storms producing heavy rain from Philadelphia to New York City. Even though most areas received 0.50 – 1.00 inch of rain, it was not enough to compensate for the dry pattern and the U.S drought monitor classified northern New Jersey and southern New England as abnormally dry on August 13th. As the graph below shows, the U.S Drought Monitor expanded the "abnormally dry" region into southern NJ and northern New England by the end of the month.

 

 

Heading into mid-August, Mother Nature turned up the heat with consecutive days in the 90s from August 15 – 19th. New Brunswick, NJ even set a new record high temperature on the 18th at 98 degrees, surpassing the previous record of 96 degrees set in 2002. During this period, most rain fell from isolated hit and miss thunderstorms and showers, mainly in New England. 

However, by the 19th to 21st, more widespread and heavy rain moved into the Northeast. First, slow moving and training storms led to flash flooding in areas of New Jersey on the 19th. Scotch Plains, NJ and Mountainside, NJ were severely flooded as 8 inches of rain inundated western Union County. In fact, high flood waters submerged cars on Route 22! Then, an incoming cold front on August 20th into the 21st brought heavy rain and flash flooding into eastern Pennsylvania and portions of New Jersey. While most received between 0.25 to 0.50 inches of rain, locally strong thunderstorms in New Jersey produced “bullseyes” of 2 - 4 inches in Sussex, Cape May and Monmouth Counties.

The final week of August then turned quiet with plenty of warm and dry days. Temperatures started in the mid – upper 80s before a cold front pushed through from the 24th into the 25th, leading to the only significant rain event of this last week. While areas of heavy rain and isolated strong storms hit those from Washington D.C to Baltimore, MD and portions of Connecticut, eastern Pennsylvania and New Jersey missed out on much needed rainfall. Temperatures briefly cooled behind the front on the 27th and 28th before high pressure quickly regained control, giving the Northeast a hot last weekend of climatological summer as temperatures soared back near 90. 

For many across the Northeast, August 2015 finished 1 – 3 inches drier than normal with Atlantic City, NJ and Philadelphia, PA ranking the month as the 4th and 6th driest August of all time, respectively. See the table below:

 

Temperature wise, a warm pattern dominated the month with New York City citing a record 53 consecutive days at or above 80 degrees starting from July 9, 2015 to August 31st, 2015 (previous record was 41 days in 2011). With the heat expected to last into early September, this record will likely increase. Central Park, NY ranks the month as its third warmest August of all time with Philadelphia, PA recording 11 August days at or above 90 degrees, the highest number since August 2010!