by
Josh Griffin
Nov 22nd, 2010
As residents of Kwajalein may have noticed, this past October was a little rainy. There was only one day, October 2, where no rain was observed at the weather station. The month ended with 18.56” of rain measured, which is 7.10” above the normal rainfall total for October. The weekend of the 17th and 18th was particularly exciting with the weather station measuring 8.56” of rainfall over a 2-day period as an active Intertropical Convergence Zone allowed for deep convection to continue reforming over Kwajalein Atoll.
Looking back on over 58 years worth of daily rainfall data, the weather events on the 17th and 18th really stand out within the recent climatology for Kwajalein. The total rainfall produced on those days was the greatest 2-day rainfall total that has been observed in over 15 years. The last similar event occurred on June 2nd and 3rd of 1995 when we received 8.86” of rain. In fact, the last time we had a greater 1-day rainfall total was also associated with this same event in 1995. The rainfall observed on October 17th was 5.04” and the last occurrence of such a heavy rainfall event was on June 2, 1995, when 8.82” fell over Kwajalein. Looking back across the entire climatology of Kwajalein, the 2-day total on October 17/18 was the 8th wettest 2-day event on record, and the daily rainfall total on October 17 was the 18th wettest day on record (over 21,000 days)! Looking at the monthly rainfall totals, this October was the 6th wettest October on record dating back to 1945.
The rainy weather throughout the month helped snap a 3-month drought that the atoll has been experiencing. The Pacific ENSO Applications Climate Center has a monthly climate discussion that focuses on the impact of El Niño and La Niña conditions throughout the Pacific Islands. The discussion, which occurred after the events on 10/17 and 10/18, concluded that it would take near drought conditions for the three month period of October, November, and December to be less than above average. They also concluded that La Niña conditions (colder sea surface temperatures) are expected to persist through the new year. La Niña conditions usually lead to below normal rainfall totals for Kwajalein, but the rain event in October was likely triggered by a phenomenon called the Madden-Julian Oscillation (MJO). It was concluded that while the MJO would likely lead to above normal rainfall through roughly the middle of November. For the remainder of November and December, rainfall activity is expected to be near-normal or slightly below-normal due to persisting La Niña conditions.