Warm and Mainly Dry August
Record Summer Heat and Local Drought Conditions
August/Summer 2010 Overview

Dr. David A. Robinson
New Jersey State Climatologist
Center for Environmental Prediction, School of Environmental and Biological Sciences/NJAES, Rutgers University
September 6, 2010

August Overview

Since spring, New Jersey has been encased in one of the more persistent episodes of above-average temperatures and below-average precipitation on record. More on the longevity of this event will be covered later in this narrative. First, let's take a look at this past August. The monthly preliminary average temperature of 75.2° was 2.4° above average. This makes it the 10th warmest August since statewide records commenced in 1895 (table 1). Six of the ten warmest Augusts have occurred in the past ten years.

Rank Year Aug Temp
1 2005 77.4°
2 1955 76.2°
3 2002 76.2°
4 1900 76.0°
5 2001 75.8°
6 2009 75.6°
7 1988 75.5°
8 1980 75.4°
9 2003 75.4°
10 2010 75.2°

Table 1. Ten warmest Augusts across New Jersey since 1895

While several cloudy days from the 23rd-25th resulted in rarely-experienced below-average maximum temperatures, on sixteen afternoons maxes of 90° or higher were experienced somewhere in NJ. Maxes from 90° to 94° occurred on August 3, 6, 7, 16, 19 and 20. On the 4th, Hillsborough (Somerset County) topped out at 95°, with the same high reached at New Brunswick (Middlesex) on the 5th and again at Hillsborough on the 8th. Top honors went to Hillsborough and Sicklerville (Camden) on the 9th when both stations reached 96°, to the 98° reading at Hammonton (Atlantic) on the 10th, 97° at Mansfield (Burlington) on 11th and 96° again at Hammonton on the 17th. It wasn't until the 29th that maxes once again equaled or exceeded 95°, with a 96° high at five different locations on the 29th, and 95° at Mansfield and Hammonton on the 30th. Interestingly, it was the last day of August that was hottest, with 99° reached at New Brunswick and Mansfield. Only the highest ridges in the northwest corner of the state failed to top the 90° mark, with the High Point Monument (Sussex) station at 1800' elevation peaking at 86°.

Around NJ, the 90° mark was reached on fourteen days in New Brunswick, eleven at Newark (Essex) and Pomona (Atlantic), ten at Woodstown (Salem), nine in Haworth (Bergen), six at Pequest (Warren), two at Seaside Heights (Ocean) and on zero days at the High Point Monument.

There were several cool mornings. The 7th saw the temperature fall to 49° at Walpack (Sussex), but it wasn't until the 27th when a location would fall back into the 40°s again. On that date, the Walpack station as out of commission, and Pequest was coolest at 46°, with six counties having stations in the 40°s. Pequest dropped to 45° on the 28th (though cool conditions were not as pervasive as the previous morning) and 48° on the 29th.

Rather dry conditions prevailed across New Jersey for most of the month. The preliminary average rainfall was 2.42". This is 2.14" below average and ranks as the 15th driest August on record. The northeast faired best in the rainfall department, with a maximum of 8.15" falling in Charlotteburg (Passaic), followed by the Passaic County communities of West Milford (7.06") and Hawthorne (6.95"). The top totals in Bergen County included 6.64" at Ramsey, 6.21" in Glen Rock and 6.19" in Oakland. On the low end were communities in coastal and central areas. Only 0.48" fell in Burlington (Burlington), with two stations in Jackson (Ocean) coming in with 0.63" and 0.64". Moorestown (Burlington) totaled 0.74", Princeton (Mercer) 0.76" and Lawrence Township (Mercer) 0.84".

August 1st saw 0.91" fall in Lebanon (Hunterdon) and 0.90" at Point Pleasant Beach (Ocean). The 5th brought 1.11" to a station in Liberty Township (Warren) while another station in town caught 0.51". Woodstown (Salem) received 0.86" on the 12th, while Wanaque (Passaic) had 0.61". The 15th -16th brought another 0.68" to Wanaque, 0.66" to Sparta (Sussex) and 0.65" to Blairstown (Warren). Early on the 17th, 1.05" fell in Holmdel (Monmouth), 0.88" in Montgomery (Somerset), 0.57" in Saddle Brook (Bergen) and 0.55" at Harrison (Hudson).

Heavy rain fell in extreme south Jersey from the 18th into the 19th. Impressive totals in Cape May County included: Wildwood Crest 3.91", West Cape May 3.75", Middle Township 3.00" and 3.10", Linwood 2.98", and Sea Isle City 2.86". Estell Manor (Atlantic) caught 2.84". The northeast corner of the state saw downpours on the 22nd that totaled 4.91" at Ramsey (Bergen), 4.49" and 3.31" at stations in Hawthorne, 3.54" in Oakland and 2.97" in River Vale (Bergen). A narrow band of heavy rain also moved through central NJ, where one station in Hillsborough (Somerset) received 2.73", while five miles away another township station only saw 0.63". All told, 27 of the 147 reporting CoCoRaHS stations had totals exceeding 2.00", while on the low end, Egg Harbor Township (Atlantic) could only muster 0.04".

Another shot of rain in far northern NJ on the 23rd brought an additional 2.43" to Charlotteburg, 1.49" to West Milford and 1.13" to Hardyston Township (Sussex). Rains visited northeast Monmouth County on the 24th into the 25th (Fair Haven 0.99", Shrewsbury Township 0.88" and Red Bank 0.86"). The 25th also saw the extreme northwest corner of the state doused with 1.67" at both High Point stations separated by several miles, and 1.57", 1.40" and 1.16" at three stations in nearby Wantage (Sussex).

Atmospheric pressure differentials were not large over the course of August. The lowest pressures of between 29.60" and 29.65" were observed on the 5th and the highest, in the 30.25"-30.30" range, occurred on the 29th. As a result of this and the limited amount of thunderstorm activity, winds failed to gust above 34 mph at any station in the state. This top gust was observed on the 23rd at the Atlantic City Marina (Atlantic) and Seaside Heights (Ocean).

The northeast rains on the 22nd brought the most acute impacts to New Jersey during August. Several streams and rivers reached bank full or minor flood stages. This proved helpful to reservoirs in the area, in several cases bringing them back up to seasonal normal levels after having been almost 20% below normal. Moderate drought conditions prevailed in central and coastal counties south to Atlantic. Water supplies remained at adequate levels in these areas, however streams and rivers were running exceedingly low and un-irrigated crops and natural vegetation were greatly stressed. Overall, there was terrific vacationing weather, though the high temperatures put a strain on electric bills.

Summer 2010 Overview

Compared to all past summers (June-August) since statewide record keeping began in 1895, this past summer was the warmest. At 76.1°, the average temperature was 3.9° above normal, a full half degree warmer than the previous record (2005) and 1.5° above the 3rd highest average (table 2). Of the eight warmest summers, six have occurred since 1999.

Rank Year Summer Avg Temp
1 2010 76.1°
2 2005 75.6°
3 1949 74.6°
4 1999 74.5°
5 2002 74.4°
6 2006 74.3°
7 1955 74.1°
8 2008 74.0°
9 1900 73.9°
10 1943 73.8°
11 1973 73.8°
12 1988 73.8°

Table 2. Warmest summers across New Jersey since 1895

June saw fourteen afternoons equal or top the 90° mark in Pomona (Atlantic), 21 days exceeded that threshold at Newark (Essex) in July and fourteen topped that value at New Brunswick (Middlesex) in August. To provide some indication of the consistency of the heat, New Brunswick's daily average temperature was above average on 63 of the 92 days of summer. It was below average on just 24 days and average on five.

The preliminary average for summer precipitation stands at 8.27", making it the 8th driest (table 3). This is 4.57" below normal, or 64% of average. It was the driest summer since 1966, with even less rain than two memorably dry summers in the 1990s.

Rank Year Summer Prcp
1 1966 5.67"
2 1957 5.73"
3 1929 7.10"
4 1949 7.65"
5 1964 7.89"
6 1913 8.09"
7 1923 8.12"
8 2010 8.27"
9 1963 8.28"
10 1944 8.32"
11 1965 8.48"
12 1995 8.62"
13 1999 8.70"
14 1912 8.90"
15 1918 8.93"

Table 3. Driest summers across New Jersey since 1895

At least 10.00" of summer precipitation fell at one or more stations in eight counties (Sussex, Passaic, Bergen, Warren, Morris, Hunterdon, Somerset, and Gloucester) with Salem just missing this mark with one station at 9.98". Highest totals included 16.60" in Bethlehem Township (Hunterdon), 14.84" in Lebanon Township (Hunterdon), 14.67" in Glen Rock (Bergen) and 14.54" in Hawthorne (Passaic).

Moderate drought conditions developed in six counties, where 6.00" or less rain accumulated over the three-month interval (Mercer, Somerset, Middlesex, Monmouth, Ocean, and Cape May), with a station in Atlantic just above that mark with 6.11". Lowest summer totals included 4.66" in South Brunswick (Middlesex), 4.99" in Asbury Park (Monmouth), 5.03" at Point Pleasant Beach (Ocean) and 5.22" in Upper Township (Cape May).

Additional Intervals

Given the record warmth of this past summer and spring, it is not surprising that this combined period was remarkably warmer than any such period in the past 116 years. The April-August average temperature of 69.7° exceeded the previous high mark by 1.8° (table 4). The next nine warmest such intervals all have averages lying within 0.8° of each other. Seven of the ten warmest periods have occurred in the past twenty years.

Rank Year Apr-Aug Avg Temp
1 2010 69.7°
2 1991 67.9°
3 1955 67.7°
4 2006 67.6°
5 2002 67.5°
6 2005 67.2°
7 1949 67.2°
8 1959 67.2°
9 1998 67.1°
10 1999 67.1°

Table 4. Warmest growing seasons (April-August) across New Jersey since 1895

The average temperature for 2010 through August is 57.1°, making it tied for the second warmest such interval and only 0.1° off the top mark in 1998 (table 5). This is quite impressive, as absolute monthly departures of temperature from average are most often largest during the winter, thus warm or cold winters tend to dominate annual departures. Neither January nor February of this year had particularly large departures.

Rank Year 2010 Avg Temp (Jan-Aug)
1 1998 57.2°
2 2002 57.1°
3 2010 57.1°
4 1949 56.7°
5 2006 56.6°
6 1991 56.6°
7 1990 55.8°
8 1921 55.7°
9 2008 55.7°
10 1999 55.6°

Table 5. Warmest January-August intervals across New Jersey since 1895

Finally, given that November 2009 was the 2nd warmest on record, some may wonder how the past 12-month interval stacks up against the similar period in the past. It ranks 4th, behind 2001-2002, 1990-1991 and 2005-2006 (table 6).

Rank Year 12-month Avg Temp
1 2001-2002 55.8°
2 1990-1991 55.2°
3 2005-2006 55.2°
4 2009-2010 55.0°
5 1948-1949 54.9°
6 1997-1998 54.8°
7 2007-2008 54.7°
8 1998-1999 54.6°
9 1931-1932 54.5°
10 2006-2007 54.0°

Table 6. Warmest September-August intervals across New Jersey since 1895

As for precipitation, the growing season to date (April-August) has seen an average of 14.03" accumulate statewide. This ranks as the 6th driest such interval since records began and the driest since 1966 (table 7). It is 7.04" below average or 67% of average. We are indeed fortunate that March 2010 was a record wet month, as was the 12-month interval ending this past March. Otherwise much of NJ might be suffering from water shortages at this time. The latest 12-month total (September 2009-August 2010) of 52.33" ranks as 22nd wettest, and the January-August 2010 total of 31.75" is 48th wettest.

Rank Year Apr-Aug Prcp
1 1963 11.82"
2 1957 12.01"
3 1966 12.56"
4 1965 12.60"
5 1923 13.04"
6 2010 14.03"
7 1995 14.47"
8 1999 14.54"
9 1964 14.82"
10 1993 15.14"

Table 7. Driest growing seasons (April-August) across New Jersey since 1895

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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