Widely Varying Precipitation:
September 2012 Report

Dr. David A. Robinson
New Jersey State Climatologist
Center for Environmental Prediction, School of Environmental and Biological Sciences/NJAES, Rutgers University
October 7, 2012

As is often the case as we transition from one season to another, September 2012 had a wide variety of weather conditions, both from day to day and from region to region. This is certainly exemplified in the hourly temperature map that accompanies this narrative. At 7AM on September 25th, temperatures recorded at NJ Weather and Climate Network (NJWxNet) locations ranged from 34° in Basking Ridge (Somerset County) and Pequest (Warren) to 63° at the Atlantic City Marina (Atlantic). What is known as "cold air drainage" on this clear, calm morning led to the crisp, borderline frosty morning at low-lying inland locations. Meanwhile, higher elevations were milder, as seen by the 50° in Parsippany (Morris) and 45° at High Point (Sussex). The coastal warmth was due to the proximity of the communities to the still warm waters of the ocean and bays. Higher temperatures were also experienced at urban New York City and Philadelphia stations. Keep a keen eye on NJWxNet maps over the coming months and you will be sure to see this pattern emerge time and again. Meanwhile, when clouds cover the state and the wind is blowing you may not see more than a 5° range in morning temperatures.

Back to September 2012 conditions around New Jersey. The month averaged 67.1°, which is 0.9° above average (1981-2010 averaging period) and ranks as the 24th warmest September dating back 118 years to 1895. This keeps alive the string of 20 months without one being below average in the temperature department.

There were nineteen days when the daily maximum temperature reached or exceeded 80° at one or more of the over 50 NJWxNet stations around the state. Six of these saw maximums reach 85°. The hottest day of the month was the 1st when Atlantic City Marina and Bethel Mill Park (Gloucester) got to 94°. 32 other stations were between 90°-93°, with High Point Monument (Sussex) the coolest spot at 82°. On the 4th, Dennis Township (Cape May) was warmest at 88° and on the 5th Greenwich (Salem) reached 89°. The season's last 90° readings were on the 7th at Cherry Hill (Camden), Eastampton (Burlington), and New Brunswick (Middlesex). The 8th saw seven southern stations reach 88°, while on the 22nd five stations got to 85°.

On thirteen mornings the minimum temperature dipped to 45° or cooler at one or more locations. The 43° at Walpack (Sussex) on the 10th started the run of such days. The 11th, 12th, and 13th found Basking Ridge and Pequest tied for low honors at 38° (first 30°s of the season), 41° and 44°, on respective mornings. Walpack and Pequest were down to 44° on the 15th, with Pequest and Basking Ridge 40° and 39° on the 16th and 17th, respectively. Pequest stood alone at 41° on the 19th, joined by Basking Ridge on the 20th at 37° and by Berkeley Township (Ocean) at 42° on the 23rd. Three stations fell to 38° on the 24th. The 25th was the coldest morning of the month, with scattered frost observed at valley locations in the northwest. Pequest and Basking Ridge bottomed out at 34°, seven other stations were in the 30°s, and 30 locations ranged between 40°and 45°. West Cape May (Cape May) and Atlantic City Marina only reached 59°.

The year-to-date average temperature for the state is 59.1°, making this the warmest such interval on record (Table 1). This is 3.2° above the 30-year average.

Rank Year Jan-Sep Avg. Temp.
1 2012 59.1°
2 1998 58.5°
2 2010 58.5°
4 2002 58.4°
5 2006 57.5°
5 1991 57.5°
5 1949 57.5°
8 2011 57.4°
9 2008 57.1°
9 1921 57.1°

Table 1. The ten warmest January to September intervals across New Jersey since 1895.

Turning to precipitation, September's statewide average was 3.97". This is just 0.10" below average and ranks as the 48th wettest on record. Year-to-date precipitation is 30.10", which is 26th driest and 5.36" below the 30-year average.

The near-average September total belies the fact that there was an exceptional range of monthly values across New Jersey. Four locations exceeded 10", including Woodland Township (Burlington) 11.76", and in Ocean County, Berkeley Township 10.65", Toms River 10.58", and Pine Beach 10.23". Wildwood Crest (Cape May) was the driest location with 1.73", followed by the central Jersey communities of North Brunswick (Middlesex) 2.19", Ewing Township (Mercer) 2.23", and Montgomery Township (Somerset) 2.27". It is exciting to report that 263 Community Collaborative Rain, Hail and Snow (CoCoRaHS) network citizen scientists contributed to this month's evaluation, although not all reported frequently enough to generate a monthly tally.

The precipitation action began on the 2nd, with Monmouth County and the northeast corner of the state getting the heaviest rain. Two Holmdel (Monmouth) gauges caught 2.16" and 2.54", with the Bergen County locales of Haworth 1.63" and Tenafly 1.50" posting hefty totals.

A complex pattern of thunderstorms impacted NJ from the 3rd-5th. In some locations they were accompanied by flooding rain and damaging winds, including NJ's first tornado of 2012. A deluge in southern Burlington and the much of Ocean counties from late on the 3rd into the morning of the 4th brought unofficial reports of over 10". National Weather Service radar estimates suggest they may have been legitimate observations. Later on the 4th, a very unstable atmosphere produced more heavy rain (especially in the northwest corner of NJ), a funnel cloud spotted by an ONJSC staff member near Chatsworth (Burlington), and a confirmed tornado in Mount Ephraim (Camden). The EF0 twister (winds near 70 mph) damaged some roofs, felled trees, and led to power outages. There were no reports of injuries. More rains fell on the 5th, particularly in coastal Ocean County. Official rainfall totals for this 3-day period included 9.05" in Woodland Township (Burlington), and in Ocean County 8.92" in Toms River, 8.79" and 7.62" in Berkeley Township, and 8.75" at Pine Beach.

The 6th brought West Cape May (Cape May) 1.22" and Middle Township (Cape May) 0.50". Scattered thunderstorms on the 7th saw Medford Lake (Burlington) receive 0.80" and Lebanon (Hunterdon) 0.70". A local storm in Demarest (Bergen) sparked a lightning strike that killed a local man. Tragically, this was the third lightning death of the year in New Jersey. Small hail fell from this cell in Harrington Park (Bergen).

Separated by well over a week of almost completely dry weather (with several "top ten"-quality days), the next two significant rain events were the result of potent squall lines crossing the entire state. The first, during the late afternoon and early evening of the 8th, brought hail to River Vale (Bergen), tree-damaging winds to most counties, and 0.40"-0.60" of rain to much of the state. The heaviest rain fell in Haworth (Bergen) 1.42", West Caldwell (Essex) 1.37", Wayne (Passaic) 1.37", Howell (Monmouth) 1.30", and Medford Township (Burlington) 1.97". Winds gusted to 59 mph in Atlantic City (Atlantic), 49 mph at High Point Monument (Sussex), and 48 mph at Bivalve (Cumberland). Five other NJWxNet stations had gusts from 40-49 mph and seven from 30-39 mph.

The squall line on the 18th brought widespread wind damage, power outages, and heavy rain across NJ. Atlantic City again received a 59 mph gust, with Bivalve at 51 mph, and Point Pleasant (Ocean) and Woodstown (Salem) at 49 mph. Five other stations had gusts in the 40-49 mph range and seven between 30-39 mph. Rain from this late afternoon and evening onslaught added to totals earlier in the day, resulting in as much as 3.29" at High Point (Sussex), 3.21" in White Township (Warren), and 3.01" at Oxford Township (Warren). 41 CoCoRaHS stations reported 2.00"-2.99" and 142 observed 1.00"-1.99". There was a consistent reduction in rainfall from northwest to south east portions of the state, with the coastal south mostly seeing less than 0.50".

Inland southern locales received the most rain from a system on the 22nd into the early hours of the 23rd. The Burlington County communities of Mansfield 1.07", Burlington 0.95", and Moorestown 0.88" topped the list. A lengthy event from the morning of the 26th into the 27th brought scattered moderate totals in thundershowers to portions of central and southwestern NJ. Franklin Township (Somerset) received 0.60" and two South Plainfield (Middlesex) gauges caught 0.59" and 0.55". From late on the 27th into the morning of the 28th rain fell over the northern half of the state and in Cape May County. Jefferson Township (Morris) received 1.64", West Milford (Passaic) 1.18", and Hardyston Township (Sussex) 1.06". Quite localized showers sprang up on the afternoon of the 30th, one thunderstorm cell bringing pea size hail to Raritan (Somerset), Bound Brook (Somerset), and Edison (Middlesex). Some of this hail and 0.33" of rain quickly fell on a community fair in Raritan where several of us from the CoCoRaHS program were promoting our RAIN, HAIL and snow network!

The highest barometric pressure during September was observed on the 12th and 13th, ranging from the upper 30.30"s to low 30.40"s. Pressures were lowest, in the mid 29.50"s, on the 8th.

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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