Yet another hot summer month: July 2013 Summary

Dr. David A. Robinson
New Jersey State Climatologist
Center for Environmental Prediction, School of Environmental and Biological Sciences/NJAES, Rutgers University
August 4, 2013

July 2013 marked yet another in a lengthening sequence of hot mid-summer months across New Jersey. Most notable this year was the frequency of unusually warm nighttime temperatures. Accompanying the warmth and often excessive humidity were widely varying rainfall totals, which on a statewide basis averaged above the long-term mean.


The statewide average temperature of 78.2° was 3.2° above average. This ranks as the 5th warmest July since records commenced in 1895 (Table 1). Remarkably, the most recent four Julys all are within the top six, with three other Julys from the last 20 years also populating the top 10.

Rank Year July Avg. Temp.
1 1955 79.0°
2 2011 78.8°
3 2010 78.7°
4 1999 78.4°
5 2013 78.2°
6 2012 78.1°
7 1949 77.8°
8 2006 77.3°
9 1994 77.1°
10 1901 77.0°

Table 1. The ten warmest Julys across NJ since 1895.

The warmth of July 2013 was characterized by nighttime temperatures that struggled to drop below 70°. While statewide average monthly minimums are not available, it is worth noting that on 26 days one or more of the over 50 NJWxNet stations failed to dip below 70°. In New Brunswick (Middlesex County), the more than century-long station at Rutgers Gardens (outside the core of the developed community, thus not experiencing an urban heat island effect) experienced 21 days with minimums at or above 70° with an average minimum of 69.8°. This average was not only 4.9° above the 1981-2010 normal but was by far the warmest monthly minimum on record. This exceeded the previous record warm minimum (July 1955) by 1.8° and the 21 days shattered the previous record number of 70° or warmer minimums in a month, which had been 15 in August 2005.

There were also plenty of hot July afternoons, with 18 days seeing at least one station rising to 90° or higher. This included eight-day (4th-11th) and ten-day (14th-23rd) runs. Does this mean NJ only had two heat waves in July? Well, that is the case if one considers three or more consecutive days of 90° warmth as constituting a heat wave. Thus the disinterest of those of us in the state climate office in counting the number of seasonal "heat waves". A better measure is to pay attention to the number of days exceeding the 90° threshold, statewide or at individual locations. And as seen above, it does not hurt to evaluate night time lows as well.

Hawthorne (Passaic) reached 93° on the 4th, with three other stations (including Newark Airport (Essex)) at 91°. Hawthorne saw 95° on the 5th, with three stations at 93°. Seven stations topped out at 95° on the 6th, with Hawthorne and Newark at 96° on the 7th and three locations at 95°. The 8th-11th saw state maximums of 90°-91° in communities such as Point Pleasant (Ocean), New Brunswick, Jersey City (Hudson), Piney Hollow (Gloucester), Newark, and Hawthorne.

The 14th-20th marked the most uncomfortable July interval. Accompanying scorching daytime maximums were high humidity levels, resulting in the heat index exceeding 110° at some locations during afternoon hours. Little relief was found at night, as minimums remained in the 70°s almost everywhere most nights, and even a few times were in the low 80°s in some urban and coastal locations. Hawthorne got to 94° on the 14th and Newark 93°. Newark reached 97° on the 15th, with five stations at 96° and five others at 95°. Hawthorne was 96° and six stations 95° on the 16th. New Brunswick was hottest at 98° on the 17th, with three stations at 97°. Newark baked at 101° on the 18th, when Berkeley Township (Ocean), Jersey City, and Toms River (Ocean) rose to 99°. This hottest day of the month also saw six stations at 98° and only High Point Monument (Sussex) and Bivalve (Cumberland) maxing out below 90°, with highs of 88° and 89°, respectively. The National Weather Service Cooperative station in Harrison (Hudson) rose to 102° on the 19th, with Newark and Point Pleasant at 100°. Berkeley Township and Jersey City reached 99° on the 19th, while Harvey Cedars (Ocean) was "coolest" at 84°. Point Pleasant saw 97° on the 20th, when Sea Girt (Monmouth), Berkeley Township, and Newark topped out at 96°. The 21st-23rd found three stations up to 92°, four stations to 90°, and New Brunswick to 90°, on these respective dates.

It is somewhat unusual to discuss warm minimum temperatures. However, when NJ has almost certainly not had any month in more than a century of observations with such excessive overnight warmth, attention is warranted. On 26 July days, at least one NJWxNet station had a minimum at or above 70°. This included the 1st-24th and 27th-28th. The 19th saw the warmest minimums, with 82° and 80° at Newark and Point Pleasant to go along with 81° at Jersey City and 80° at five other stations. Only Walpack (Sussex) at 67° was below 70°. The 20th saw all stations in the 70°s with the exception of Walpack at 69°. With excessive humidity levels throughout the majority of the first three weeks of July it was difficult to rid the surface and lower atmosphere of the previous afternoon's heat via outgoing radiation. Such a process works most effectively when the lower atmosphere is rather dry. While this humidity and generally moist surface conditions likely "saved" the state from even higher daytime maximums (some of the sun's energy went toward evaporation, not heating, and sometimes afternoon clouds appeared), we paid for it through the discomfort wrought by the moist atmosphere.

However, a brief drier spell toward the middle of July and a more refreshing air mass during the last week of the month resulted in ten days with minimum temperatures below 60° at one or more locations. The 12th found Walpack at 58°, and both High Point (Sussex) and High Point Monument stations fell to 59° on the 13th. The 24th saw Walpack and the Monument stations at 54°. The monthly low of 49° occurred at Walpack on the 25th, when ten stations dropped into the 50°s. Walpack was 52° on the 26th and joined at that mark by Pequest (Warren) on the 27th. Looking to the coastal plain, Berkeley Township (Ocean) and Woodbine (Cape May) were the coolest locations in the state at 58° and 59°, respectively, on the 28th. Walpack took low honors at 53° on the 29th. Statewide, the 30th was the coolest morning of July, with Walpack and Pequest down to 50° and 37 other stations between 51° and 59°. Atlantic City Marina at 66° was the mildest that morning. Walpack again fell to 50° on the 31st.

Precipitation and storms

As is often the case during the summer season with its hit and miss showers and thunderstorms, precipitation totals varied considerably across New Jersey this past July. The overall state average of 5.84" is 1.32" above normal and ranks as the 24th wettest back to 1895. As first stated in the June narrative, a point of information is warranted here. While over an inch fell in some locations on the afternoon of the June 30th, most National Weather Service (NWS) Cooperative observers had already reported for the day, as had Community Collaborative Rain, Hail, and Snow Network (CoCoRaHS) observers. Most take measurements close to 7 AM, with the historic rule being that the morning observation "ends" that particular calendar day. Thus any rain after that time on the June 30th was reported on July 1st. While this practice can be debated, one can only compare June and July 2013 with previous such months by following suit. Thus one might say that July 2013 totals are a bit inflated (by the way, it did not rain from 7AM on July 31 to 7AM August 1), and June totals minimized, despite the fact that June 2013 was the wettest on record without including the post-7AM June 30th rains.

July's storms most often had eyes on the western counties, especially from Salem up to Hunterdon where values were at least several inches above average. Meanwhile the eastern counties caught closer to average rainfall, with scattered areas, particularly along the shore, coming in several inches below average. Among the over 200 CoCoRaHS, NJWxNet and NWS Cooperative stations with complete or near complete July totals, two stations in Mount Holly (Burlington) took top honors with 14.08" and 12.72". These impressive totals were followed by 11.28" in Pennsville (Salem), 9.86" at Mount Ephraim (Camden), 9.65" in Lebanon (Hunterdon), and 9.60" in Jackson (Ocean). On the low end, only 1.55" accumulated in Lacey Township (Ocean). This is only a mere 30 miles or so to the east of Mount Holly! Other dry spots included Seaside Heights (Ocean) at 2.01", Upper Township (Cape May) 2.22", Linwood (Atlantic) 2.47", Toms River (Ocean) 2.39", Eatontown (Monmouth) 2.56", and Palisades Park (Bergen) 2.63".

The rain on the afternoon and evening of June 30th mostly fell in the far southwest and northwest corners of the state. It amounted to 1.00"-2.00" in a few locations, while over two thirds of the state had no more than a few tenths of an inch. As the 1st dawned and CoCoRaHS observers began checking their gauges a powerful thunderstorm complex entered the state through Hunterdon County. This complex rapidly made its way to the northeast, leaving NJ in the Bergen County area by mid morning. Accompanied by intense lightning, straight line winds brought down trees along its journey and the first NJ tornado of 2013 struck western Union County. The EF0 tornado touched down in Berkeley Heights at 9:17 AM, passed through New Providence and dissipated in Summit at 9:25 AM, a path of 4.8 miles. The tornado was approximately 50 yards wide and had maximum winds of 85 mph. Extensive tree damage occurred along its path, with roof damage and power outages also observed. Fortunately no one was injured. Rainfall totals for the 30th and 1st had to be bundled together due to the varying observation times of observers the morning of the 1st, some observing before the storm passed, others shortly after. Totals were as large as 3.07" in Woolwich Township (Gloucester), 2.70" in Kingwood (Hunterdon), 2.67" in Franklin Township (Hunterdon), and 2.69" at Newton (Sussex). Flash flooding occurred during the morning of the 1st.

Storms on the evening of the 2nd tracked along a line from Camden County northeast to Monmouth County. Fairfield (Camden) picked up 1.24", Freehold (Monmouth) 1.15", and Millstone (Monmouth) 1.14". The afternoon and evening of the 3rd saw moderate to heavy rainfall in storms that moved from Burlington County eastward to the Monmouth/Ocean border, with little falling elsewhere in NJ. 1.93" accumulated at Sea Girt (Monmouth), 1.90" in Point Pleasant Beach (Ocean), and 1.68" in Brick (Ocean). More storms on the 7th deposited 1.22" at Wantage (Sussex), and 0.86" and 0.72" in two Lebanon (Hunterdon) gauges. Considerably less rain fell outside of the northwest corner and Hunterdon/Morris region, however strong winds toppled trees onto homes and power lines at locations in Somerset, Morris, Essex, and Bergen counties.

Scattered thunderstorms brought less than 1.00" rainfall totals to portions of central and southern NJ on the 9th, 10th, and 11th. More significant rains fell during the daytime hours of the 12th, particularly in extreme southern areas from Salem through Cumberland and into Cape May counties. Over 2.00" fell in most of this area, with impressive totals in Cape May, including Middle Township 5.60", Lower Township 5.51", Cape May 3.43", West Cape May 3.19", and Wildwood Crest 3.12". Of the 212 CoCoRaHS stations reporting this event, 47 caught more than an inch, including some locations up the Delaware Valley to Mercer County. Other areas of the state saw less than 0.50". The persistent pattern of scattered storms continued on the 13th with the focus on Mercer County and nearby environs. In Mercer, Hamilton stations received 2.92" and 1.95", Lawrence Township 1.60", and three stations in Ewing Township 1.15", 1.11" and 1.02". Montgomery (Somerset) saw 1.58". Little rain fell once 20-30 miles away from Mercer.

The hottest spell of the month was accompanied by little to no rain. It was not until the heat began to relinquish its grip that rains returned to the Garden State. During the PM hours of 20th, southern Atlantic County and areas within 30 miles or so of this area received more than 0.50", with 1.16" in Egg Harbor Township and 1.11" in both Linwood and Estell Manor. Another zone through Hunterdon, Somerset, and northern Middlesex counties caught 0.50"-1.00", topped by 1.18" in Woodbridge (Middlesex). The late afternoon of the 21st saw storms drop 1.70" at the Atlantic City Marina (Atlantic) and 1.51" and 1.29" at Stafford Township (Ocean) stations. Little rain fell elsewhere.

The heat truly broke when a frontal system moved through NJ late on the 22nd into the early morning of the 23rd. Accompanying this were the most widespread heavy rains of the month. The heaviest fell in an area encompassing northern Burlington/Mercer/western Monmouth/northwest Ocean counties, with flash flooding ensuing. Mt Holly (Burlington) received 6.44", Jackson (Ocean) 6.07", Hamilton (Mercer) 3.77", and Millstone (Monmouth) 3.62". Northern Hunterdon/southern Warren north-northeastward to northern Passaic County also saw multiple inches of rain and flooding in spots, including 4.19" in Denville (Morris). From 0.50"-1.00" fell in most of the remainder of northern and central NJ, with 0.00"-0.50" in the southern third. Of the 232 CoCoRaHS stations reporting, 87 received 1.00"-1.99", 34 from 2.00"-2.99", 8 from 3.00"-3.99", and those mentioned above saw more than 4.00". Accompanying the severe storm in Jackson on the 22nd was a reported gustnado that took down a number of trees and lightly damaged several homes. The National Weather Service reviewed the damage and made the designation of gustnado, which typically forms in the outflow boundaries of thunderstorms. According to the NWS, they are not quite tornadoes, but they do have a rotation to them.

The final storms of July deluged portions of the lower Delaware Valley and west central NJ, resulting in flash flooding that closed major roadways for hours during the late Sunday afternoon and early evening of the 28th. Within just several hours, Pennsville (Salem) received 5.93", Mount Ephraim (Camden) 5.17", and East Greenwich Township (Gloucester) 4.55". The worst hit areas were most of Salem, Gloucester, and Camden counties, southwest Burlington, and western Cumberland. Still, within this zone, gauges in central Salem and Gloucester counties caught less than an inch. More than 2.00" fell in a bull's eye over northeast Hunterdon/northern Somerset/southern Morris. Some 68 CoCoRaHS stations of 225 reporting saw 1.00"-1.99", 20 from 2.00"-2.99", and 15 from 3.00"-3.99", in addition to reports noted above. Despite this count, most of the eastern third of the state received less than 0.50".

Wind and Pressure

While local thunderstorm winds, including the tornado on the 1st and gustnado on the 22nd clearly saw winds gusting over 50 mph, the NJWxNet only had two instances this month where a station reported a gust exceeding 40 mph. Sea Girt peaked at 47 mph on the 9th and Upper Deerfield (Cumberland) gusted to 45 mph on the 20th.

Barometric pressure was highest on the 14th, with most stations rising to the mid 30.30"s. Lowest pressures were observed on the 23rd and were mainly in the mid 29.50"s range.

For those seeking more detailed information on hourly, daily and monthly conditions, please visit the following Office of the NJ State Climatologist's websites:

NJ Weather and Climate Network
NJ Community Collaborative Rain, Hail and Snow Network
NJ Snow Event Reports

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