Republic of the Marshall Islands: While the first half of 2010 was generally dry, the month of June 2010 was extremely wet at some locations, notably at Majuro, Mili and Arno. The 20.86 inches of rain recorded at the WSO Majuro for June 2010 was the first month at or above 20 inches since October 2007, and it represents the wettest June monthly total in the climatic record. The previous June record monthly rainfall for the WSO Majuro was the 17.63 inches recorded in June 1975. In spite of this extraordinary June 2010 total, the rainfall was still below normal for the 2nd Quarter and 1st Half of 2010 at all RMI locations.

Other atolls in the vicinity of Majuro (e.g., Mili and Arno) also had large June totals, but none quite as large as the 20-plus inches at Majuro. Many atolls in the northern RMI had a very dry May, which negated June's enhanced totals in the quarterly and half-year summaries. The RMI has been dry for a long time. The long-term climate records at Kwajalein and at Majuro (which begin in the early 1950s) show a long slow decline of mean annual rainfall that is statistically significant. At the WSO Majuro, the downward trend of annual rainfall is such that there is now a loss of nearly 20 inches of annual rainfall during the 2000s versus the 1950s. At Kwajalein, the loss of annual rainfall over the same time period is approximately 14 inches.

Republic of the Marshall Islands Rainfall Summary 2nd Quarter and 1st Half 2010

Climate Outlook: A weather pattern similar to that seen during 2008 has developed in the western North Pacific. This pattern features widespread easterly low-level winds, tropical cyclones pushed to the west of normal, a delayed tropical cyclone season, and a weak (or absent) monsoon trough. In this pattern, the trade-wind trough dominates the weather of the RMI. Low pressure systems in the upper atmosphere (TUTT cells) passing north of the RMI modulate the deep convection, and help to bring bouts of heavy rain showers to the atolls. During 2008, this type of anomalous weather pattern brought below normal rainfall to most of the RMI throughout the year. However, recent TUTT cell activity and trade-wind trough cloud clusters producing episodes of heavy rain showers bode well for near-normal rainfall throughout the RMI for the rest of 2010.

Because of the easterly winds expected to dominate the low-level wind pattern across Micronesia and the equatorial Pacific, the sea level should continue to rise throughout Micronesia. Sea-level anomalies should approach or exceed those seen in the region during 2008. Higher-than-normal sea level will expose the atolls of the RMI to a heightened risk of coastal inundation, especially towards the end of the year (late November and December 2010). At this time of the year, the extra-tropical, low pressure systems that move eastward from Japan may produce large northerly swells that will move out of North Pacific waters and pass through the RMI causing coastal inundations on some atolls where similar conditions (large waves coupled with higher-than-normal sea level) caused sea inundation in December 2008. The large waves of 2008 were a 30 to 40-year event (or longer), so waves of this magnitude are not forecasted at this time, but any large wave event coupled with higher-than-normal sea level poses an enhanced risk of coastal inundation.

Forecast rainfall for the Republic of the Marshall Islands from July 2010 through June 2011 is as follows:

Forecast rainfall quantities represent BEST ESTIMATES given the probabalistic forecast for each particular season and station.

source: UOG-WERI