Sept. 2018 was warm, rainy

Labor Day weekend brought with it weather quite normal for southern New Hampshire to start fall but heat and humidity would make a quick return for most of the remainder of the first week of September. For the second straight month heavy rainfall would encompass the Gate City.

After a couple of nice days to start the month New Englanders would have to endure another spell of hot, oppressively humid weather. The third heat wave of the year and first of the fall would occur from Sept. 4-7, and would include a record tying high of 91 on the 6th.

The high for the month of 93 would occur both on the 4th and 7th. A record high low temperature would also be recorded on the 4th with 70 degrees bettering the mark of 69 from 1904.

Temperatures would calm down some for the middle and end of the month but a few more spikes of warmth would include another 90 degree day on the 17th. A second record high low temperature of 65 degrees would be recorded on the 18th beating out 64 from 1992.

As was the case during August night-time temperatures accounted for most of the above normal character of the month. The average low was 6.3 degrees above normal while the average high was 2.1 degrees above normal.

Abundant cloudiness, moisture, and rainfall helped maintain our nighttime warmth last month. Cloudiness and high dew points act as a blanket holding in the warmth left from the daytime. The notable increase in the number of trees around the region during the past several decades also helps hold in the warmth at night.

The monthly average temperature for Nashua was 65.5 degrees for September, a surplus of 4.2 degrees. September was the 6th warmest out of 125 years of temperature records for Nashua.

To compare with our state capital in Concord, the average temperature of 64.6 degrees tied with 1877 for the 5th warmest September. Complete records go back to 1868 for Concord.

Five more 90 degree days were recorded for Nashua during September raising the yearly total to 26, 13 more than normal. The record number of 90 degree days is 35 from 1955.

We can look to the tropics for the reason why we had another warm September. Much like September 2017, warmth was spewed northward at high levels of the atmosphere as exhaust from hurricane activity far to our south.

This exhausted air from a hurricane moves outward for hundreds of miles in all directions 6 to 8 miles up and creates an upper level ridge. You may have heard people say that for a day or two before a hurricane hits in the tropics that is becomes sunny and hot. This is why that happens.

Non-tropical storms that we see at our latitude gather their energy from the jet stream and develop in an almost opposite manner to tropical systems. Tropical systems are strongest near the surface while non-tropical winter storms grow stronger as one goes higher.

Rainfall was no stranger to the southern New Hampshire during September. Nashua’s total of 8.47 inches was 4.75 inches above normal. September was the 5th wettest of record for Nashua dating back 136 years.

Four separate moisture laden systems were felt with the heaviest coming on the 18th as the remains of Hurricane Florence found their way right across our area. Nashua saw 4.60 inches of rain pelt down in just under 12 hours. Short term urban and small stream flooding was noted around the area.

A daily rainfall record was set for the 19th with 4.10 inches. The old mark of 2.02 inches was set in 1996. Tropical systems are noted for bringing copious amounts of moisture with them and can deposit very hefty totals in short order.

As Florence drifted into the Carolinas it left more the 2 feet of rain in some areas due to the slow movement. By the time this system reached us it still contained lots of water but had lost all of its’ wind due to the long term interaction with land.

2018 has surged into the wet category with the past 2 wet months under our belt. 40.58 inches have fallen on Nashua since New Year’s Day, 5.16 inches above normal.

New England continues to be in a hurricane drought. Since 1851 there have been 15 land-falling hurricanes on the New England coast, but only 3 since 1960. The last land-falling hurricane was Bob in 1991 and the 27 years since Bob are the longest stretch we’ve gone during the 167 year period without a hurricane hitting our coast. Let’s hope this stretch goes on longer.

Frosty nights tend to become more common during an average October. The average date for the first killing frost, a temperature of 28 or below, is Oct. 13 for Nashua, sooner a few miles from the downtown center. The earliest freeze of record is Sept. 16 while the latest is Nov. 10, a window nearly 2 months wide, so expect considerable variability from year to year.

A typical October starts to bring a few blustery days with fractured sunshine, along with the beginning of the coastal storm season. Every few years we can even see a few flakes of snow during the later days of the month and about every 200 years we might even see a heavy snowstorm such as the one we experienced 7 years ago.

On October 17, 1947 the mercury soared to 91 so it’s probably a good idea to be prepared for just about anything. Tropical storms can be an infrequent visitor to our region during October.

September Facts and Feats dating back to 1884

September 2018

Average Temperature

65.5 degrees, 4.2 degrees above normal.

Warmest September

67.3, 2015.

Coolest September

55.7, 1956.

All-time September High

99, Sept. 2, 1953.

September 2018 High

93 on the 4th and 7th.

All-time September Low

23, Sept. 28, 1947.

September 2018 Low

42 on the 25th and 30th.

September 2018

Precipitation

8.47 inches, 4.75 inches above normal.

2018 Precipitation

to date

40.58 inches, 5.16 inches above normal.

Wettest September

11.53 inches, 1954

Driest September

0.11 inches, 1948