Warm and Wet August 2009, Wet and Surprisingly Not Cool Summer 2009

Dr. David A. Robinson
New Jersey State Climatologist
Center for Environmental Prediction, School of Environmental and Biological Sciences/NJAES, Rutgers University
September 5, 2009

August Overview

Following a cooler-than-average first half of the summer, warmer-than-normal temperatures invaded New Jersey during the last week of July. These conditions persisted through most of August, during which statewide temperatures averaged 75.5°, which is 2.7° above normal. This ties this month with 1988 as the 6th warmest since records began in 1895. Notice from the list below that five of the ten warmest Augusts of the past 115 years have occurred during the past nine years.

Rank Year Aug Avg Temp
1 2005 77.4°
2 1955 76.2°
3 2002 76.2°
4 1900 76.0°
5 2001 75.8°
6 2009 75.5°
7 1988 75.5°
8 1980 75.4°
9 2003 75.4°
10 1937 75.1°

Over the course of the month, heavy rain fell from time to time and place to place, resulting in a state average of 7.28". At 2.72" above average, this ranks as the 12th wettest on record and is the highest total since August 1990. Local monthly totals measured by approximately 90 CoCoRaHS observers ranged from an impressive 12.90" in Lawrence Township (Mercer County) to 3.65" just 40 miles to the east in Middletown (Monmouth). Another Lawrenceville observer reported 12.10", with two other Mercer County communities reporting over a foot of rain (Pennington: 12.51" and Washington Township: 12.25"). Eleven other locations received 10" to 12". The second and third lowest totals in the state were found in Monmouth County, with 3.96" in Eatontown and 4.13" in Holmdel.

Breaking notable events down on a daily basis, the 2nd saw heavy rains falling in west-central locales. As seen in the accompanying photograph, flash flooding resulted from the 3-plus inches that fell in High Bridge (3.51") and Kingwood (3.41")—both in Hunterdon—and 3.43" in Lawrence Township (Mercer). The first 90° readings of the month occurred along the central coast on the 5th, with both Seaside Heights and Toms River (both in Ocean) reaching that mark. The 7th and 8th had the two coolest mornings until the last day of the month, with Walpack (Sussex) dropping to 48° and 46° respectively and other cooler locations in the low 50s. Next up was a Camden County downpour on the 10th, with Lindenwold receiving 2.39" and Sicklerville 2.20". Statewide, the 10th was the warmest day of the month and, unless September has a surprise in store, of the 2009 warm season. Only the higher elevations of the northwest stayed in the upper 80s, with all other locations, including the shore, topping 90°. Hillsborough (Somerset) and New Brunswick (Middlesex) led the way at 95°. Only a local thunderstorm in northern Sussex brought some residents relief, where 1.11" fell at Wantage and the wind gusted to 46 mph (the highest recorded NJ wind gust of the month). Another hot day on the 11th saw Toms River reaching 92°.

Two stormy days followed, with several southern counties the wettest on the 12th, including 2.51" in Hamilton Township (Atlantic) and 2.43" in Stafford Township (Ocean). On the 13th the northwest received 1.88" in Sparta (Sussex) and 1.79" in Knowlton Township (Warren). As measured by consecutive days with maximum temperatures equaling or exceeding 90°, the first (and only) major heat wave of the summer occurred from the 15th to 21st. Multiple locations cracked this mark on each day, with several communities doing so on each of these 7 days. The hottest locations on each day included five stations at 91° on the 15th, Haworth (Bergen) at 94° on the 16th, six stations at 94° or 95° on the 17th, Hillsborough (Somerset) at 93° on the 18th and 92° on the 19th, Woodbine (Cape May) reaching 92° on the 20th, and three locations at 93° on the 21st.

Only a few scattered thunderstorms popped up during the heat wave, including one that dropped 0.98" at New Brunswick on the 18th, the same day a 41 mph gust accompanied a storm at Seaside Heights. A sign of the heat slowly beginning to break was more widespread storms from the afternoon of the 21st through to the afternoon of the 23rd. Totals exceeded 2" at over 50 NJ stations, with Pennington (Mercer) deluged with 5.78". Four CoCoRaHS observers in Lawrence Township (Mercer) received between 4.00" and 5.33", while Hamilton Township and Folsom (each in Atlantic) accumulated 4.19" and 4.02", respectively. Flash flooding occurred during some of the local downpours, with the Assumpink Creek cresting over two feet above flood stage in Trenton (Mercer). Enough rain fell in the Millstone River basin (western Monmouth, Mercer and Somerset counties) to raise it to 1.5 feet over flood stage at Blackwells Mills on the 23rd. More hefty totals followed on the 28th and 29th, especially in Cape May County, where a series of storms dropped as much as 4.20" in Upper Township, 3.94" at Cape May Courthouse and 3.70" in Lower Township.

This wet pattern broke by the 30th, with the coolest overall minimum temperatures of the month perhaps fittingly occurring on the 31st. Walpack bottomed out at 46° and Pequest (Warren) at 49°, with all but coastal stations no warmer than the 50s.

Summer 2009 Overview

If you think New Jersey had a wet summer, you are correct! The statewide total for June through August was 19.18". This is 6.34" above average and ranks as the 5th wettest summer since 1895 and the wettest since 1975 (see table below). Three diligent observers in Lawrence Township (Mercer) recorded the largest seasonal totals, coming in at 26.74", 26.31" and 26.19". Next wettest was Washington Township (Mercer) with 25.47", followed by Califon (Hunterdon) with 24.37" and Glen Rock (Bergen) with 23.74". The lowest totals were found in three counties, including Eatontown (Monmouth) at 15.31", Middle Township (Cape May) with 15.45" and Bridgeton (Cumberland) with 15.65". Even these values are above average, explaining why reservoirs are nearly full as summer ends when they are normally close to 75% of capacity. Also, all the Department of Environmental Protection's drought status categories in each of NJ's six drought regions are at or above normal for the first time since May 2007. Categories include 90 day precipitation, 90 day stream flow, groundwater levels and reservoir levels. It certainly was a very green summer across the Garden State.

Rank Year Summer Total Prcp
1 1928 19.67"
2 1938 19.64"
3 1903 19.50"
4 1975 19.29"
5 2009 19.18"
6 1897 18.55"
7 1945 17.98"
8 1967 17.94"
9 1942 17.82"
10 1919 17.79"

If you think New Jersey had a cool summer, you are incorrect! The June-August average temperature was 71.9°. While this is 0.3° below the 1971-2000 average (most often used to determine departures), it is spot on with the 1895-2008 average. It is also right at the median value. While June was the 25th and July the 19th coolest on record, the warmth of August counterbalanced the first two months to bring about the near-normal temperature. In some defense of the vast majority of people who believe the summer was cooler than normal (including 68 of the 70 students in my Geography of NJ class), the average maximum temperature in June was more anomalously cool than the minimum, while August's minimum was more anomalously warm than the maximum. Thus the coolness of June manifested itself more when you were awake, while the warmth of August was more apparent at night. Also, there was only one heat wave, where maximum temperatures equal or exceed 90° for at least three consecutive days, that being the seven-day episode in August. Of course some NJ locales also had a four-day heat wave from April 25-28!

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

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