A typical month in New York sees about four inches of precipitation, and storms that drop an inch or more occur about once or twice each month. However, the jet stream occasionally becomes stuck in a pattern that results in storms coming our way in rapid succession. Additionally, there are times when frontal systems stall for a number of days (the last thing you want to hear as a summer weekend approaches). When these types of atmospheric situations occur copious amounts of precipitation can be the result. (Conversely, the same dynamics can create extended periods of dry weather.)
Rather than highlight individual rainstorms, this analysis looks at stretches of time when multiple storm systems produced excessive precipitation over the course of a few weeks or more. What follows is a rundown (or is it "raindown"?) of the most rain-drenched periods New York City has experienced since 1970 (thru 2018):
- Aug. 9 - Sept. 8, 2011 (23.16" in 31 days) - What a way to end a summer, as seven days had more than an inch of rain, with three storm systems dumping more than five inches. This included 6.87" from Hurricane Irene at the end of August. The rain that fell during these 31 days accounted for nearly 1/3 of the year's total precipitation. Interestingly, in the midst of this deluge, there was an 8-day stretch in which no rain fell.
- Oct. 30 - Dec. 31, 1972 (19.53" in 63 days) - During this 9-week period (making it the lengthiest of the rainy spells listed), there were five rainstorms of one-inch or more and another five that produced between 0.90-0.99". By far, the biggest storm, was the gully-washer of November 8 that produced 5.60", most of which fell in just 12 hours.
- May 8 - June 14, 2013 (17.60" in 38 days) - This extended wet spell followed one of the driest Aprils on record (1.31"). There were six days in which an inch or more of rain fell, including the first day of the period when 3.01" fell during the AM rush hour. The most rain fell when tropical storm Andrea visited the area, dumping 4.77" between June 6-8. Andrea was the second earliest tropical system to affect NYC and produced the second biggest June rainstorm on record.
- Feb. 10 - Mar 30, 2010 (17.28" in 49 days) - This 7-week period of inclement weather was comprised of two very active periods, each about two-and-a-half weeks long, separated by two weeks of tranquil weather. It was also somewhat unique because of a substantial amount of snow fell. In less than three weeks, 36" piled up in February from snowfalls of five, ten and twenty-one inches. Then, in March, there were two intense nor'easters on March 13 and March 29-30, each flooding the area with about four inches of rain. The storm on the 13th was particularly fierce because of winds in the 40-75 mph range. The 17.28" of precipitation that fell in these seven weeks accounted for 35% of the year's precipitation.
- Nov. 7 - Dec. 21, 1977 (17.11" in 45 days) - More than half of the rain fell during one of New York's all-time biggest rainstorms. On Nov. 7-8, 9.19" fell for 38 consecutive hours, with seven inches pouring down in a twelve-hour period between 2 AM-2 PM on the 8th.
- Oct. 7-25, 2005 (16.72" in 19 days) - Although it ranks sixth, this may be the most impressive of all our "monsoons" because of how few days it took to amass this amount of rain. In less than three weeks, the rain that fell was comparable to four months of rain. Seven days had more than an inch of rain (and two reported 4.26"). More than half of the rain fell in a 3-day period, between Oct. 12-14, when 8.55" was measured. And in the midst of all this rain, there was a stretch of seven days of dry weather (similar to what occurred during the deluge of 2011).
- July 12 - Aug. 22, 2018 (15.77" in 42 days) - There was a 7-day streak from July 21-27 in which 2.89" of rain fell; a near identical amount fell on 8/11; and on 7/17 a torrential downpour produced 2.24" in little more than an hour. And nearly eight inches fell on seventeen other days during this six-week period.
- April 4-27, 2007 (14.07" in 24 days) - More than half of the rain came from a nor'easter on April 15-16 that dumped 8.41" of rain over 36 consecutive hours. There were two other days during this period that picked up more than an inch of rain. During this rainy month temperatures were four degrees below average, including a stretch of sixteen days in a row in which temperatures were cooler than normal.
- May 21 - June 22, 2003 (12.83" in 33 days) - Ten days had rainfall of more than half-an-inch, with the most being 2.75"on June 4. Two-thirds of the days reported some rain. Besides being wet, this nearly 5-week period was also cool, with temperatures 5.5 degrees below average.
- Aug. 5-29, 1990 (12.36" in 25 days) - Nearly ten inches of rain fell over six days, much of it coming down during thunderstorms. On Aug. 10, 4.64" fell during two strong thunderstorms, one in the early AM and one in the early evening. The evening storm dumped nearly two inches of rain in an hour.
- July 6-25, 1975 (11.73" in 20 days) - Nearly twelve inches of rain fell in just under three weeks, much of it from thunderstorms that dumped large amounts of rain in very brief periods of time. Six days received more than an inch of rain and four thunderstorms produced more than inch of rain in an hour.
- Sept. 8-29, 2004 (11.34" in 22 days) - Most of the rain came from three tropical storms: Frances (9/8) dumped 3.77"; Ivan (9/18) contributed 2.17"; and Jeanne (9/28-29), the biggest rain producer of all, dumped 4.66".
- Dec. 5, 1973 - Jan. 4, 1974 (10.74" in 31 days) - There were six rainfalls of one-inch or more between Dec. 5-26, with the biggest rainfall being 2.65" on Dec. 20-21. Measurable rain fell during 3/4 of the days during this wet stretch of day, the highest percentage of any period on this list.
Honorable Mentions Between March 1 and April 25, 1983, 24.56" of rain fell - enough to make it the rainiest period on the above honor roll. However, 1983's precipitation totals were invalidated after it was determined that Central Park's rain gauge had been broken for much of the year. Therefore, I can't award the top spot to this period. However, so much rain fell during this nearly 8-week period (there were ten rainstorms of one-inch or more), that even if the amount was discounted by 33%, the adjusted amount would still be 16.46", good enough for 7th place.