GWC Monthly Summary – May 2025
Review – May 2025 – Wettest May on Record at GWC
The month of May 2025 was one of the wettest on record at Greg’s Weather Center. The month began quietly, but heavy rains mid-month sparked a three week period with several storms including two nor’easters. The result was the wettest May on record at GWC and the 9th wettest month ever with 6.66 inches of rain. One of the nor’easters produced the lowest pressure ever at GWC for May 31st. Temperatures were not as warm with only one 80-degree day on May 17th.
View Local Climatological Data – Greg’s Weather Center – May 2025
Rainfall – May 2025
During May 2025, there were 19 days of measurable rainfall at Greg’s Weather Center in South Plainfield. Thirteen of those days had at least a tenth of an inch of rainfall.
The wettest period of the month was May 13-16 when 2.94 inches of rain fell. The most rain in a 24-hour period occurred on May 13-14 when nearly two inches of rain fell.
The most significant rain events were on May 13-17 (2.94 inches), May 21-22 (1.15 inches), May 30-31 (0.87 of an inch), and May 15-16 (0.79 of an inch). Read more about the mid-month downpours at GWC in the blog.
| Date | Total Rainfall |
| May 13-14, 2025 | 1.97 inches |
| May 21-22, 2025 | 1.15 inches |
| May 30-31, 2025 | 0.87 inches |
| May 15-16, 2025 | 0.79 inches |
| May 3-4, 2025 | 0.55 inches |
| May 28-29, 2025 | 0.51 inches |
| May 5-7, 2025 | 0.32 inches |
| May 9, 2025 | 0.31 inches |
Wind – May 2025
While rainfall increased and temperatures decreased during May 2025, winds remained constant. The winds were about as gusty as last month, and they were the most significant during the first nor’easter, and in the wake of the 2nd nor’easter at the very end of the month.
The first nor’easter on May 21-22, produced wind-driven rain inland and fierce waves along the coast. While the barometric pressure during the first nor’easter was fairly high, the winds produced remained quite potent, especially at the shore.
Following a second nor’easter on May 30-31, a pressure gradient developed after a significant pressure drop. The pressure bottomed out at Category One Hurricane levels on the Saffir-Simpson Scale. It ended up being the lowest pressure ever recorded on the last day of May at GWC.
Temperature – May 2025
Thanks to a ton of cloud cover and nearly three weeks’ worth of days with measurable rain, the temperatures were mostly cooler than normal. There were only three 80-degree days the entire month.
May was still warmer on average than April. The average temperature for the month was 61. The highest temperature was 86 on May 17th. The lowest temperature of the month occurred on May 20th with a morning low of 42.
There were no days when the low temperature for the day was below freezing. Meanwhile, there were 28 days where the high temperature of the day was above 60. Eighteen of those days had highs of at least 70 degrees.
The average high for the month was 64 degrees while the average low was 43. The average temperature for April 2025 was 54 degrees. Looking at the diurnal temperature range, the average for the month was 21 degrees.
Pressure – May 2025
The average barometric pressure for the month was 29.84 inches of Hg or 1010 millibars at GWC. The lowest pressure was 29.14 inches or 987 millibars on May 31st while the highest was 30.20 inches or 1023 millibars on May 27th. Following that pressure peak, the barometer steadily fell 1.06 inches a little more than 35 millibars over four days.
The bulk of that four-day pressure drop occurred from midnight on May 30th until about 5:00 AM on May 31st. During those 29 hours, the pressure fell 0.72 of an inch or 24 millibars. The dramatic drop in pressure was almost characteristic of a bomb cyclone. The result was strong thunderstorms that produced another four-fifths of an inch of rain and the lowest pressure ever recorded at GWC on May 31st.
Aside from the nor’easters, there were a couple of days with severe weather threats. The first one was on May 6th and mostly affected Northern and Western New Jersey as well as Eastern Pennsylvania. The severe storms only produced a downpour at Round Valley Recreational Area in Lebanon, NJ, but spawned a tornado in Bangor, Pennsylvania. A second of severe weather nearly occurred on May 16th, but morning clouds and fog at GWC curtailed development.
