Republic of the Marshall Islands: Most atolls of the RMI have had normal to above-normal rainfall for the past 6 to 9 months. The 40.06 inches of rainfall at the Majuro WSO during the 3rd Quarter was 108% of normal. Further north, at Kwajalein, the 36.27 inches of rain during the 3rd Quarter was 112% of normal. Other stations near the Majuro WSO (e.g., Laura and Arno) were just a bit above normal with 3rd Quarter totals of 104% and 103% of normal, respectively. 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. Recent abundant rainfall in 2010 and 2011 has created a small upward bulge on the recent end of the long-term rainfall time series, but has not been sufficient to nullify the significance of the drying trend at these islands. The downward trend of annual rainfall is such that there is 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 6-decade time period is approximately 14 inches. Most locations in the islands of Hawaii are also experiencing a similar long-term decline of rainfall.

Republic of the Marshall Islands Rainfall Summary 3rd Quarter 2011

Climate Outlook: With the return of La Niña, a weather pattern similar to that seen throughout 2008 and 2010 has developed in the western North Pacific. This pattern features widespread easterly low-level winds throughout Micronesia, cool SST along the equator south and east of the RMI, and tropical cyclone activity pushed far to the west of normal. In this pattern, the rather narrow trade-wind convergence zone dominates the weather of the RMI. During 2008, this type of anomalous weather pattern was accompanied by below-normal rainfall at most of the RMI throughout that year. During 2010, however, abundant rainfall occurred at most locations. This difference was likely due to the location of the Tropical Upper Tropospheric Trough (TUTT), which produced more favorable upper-level wind patterns during 2010. Considering the overwhelming long-term drying trend, persistence, and computer guidance indicating near-normal rainfall for the next three months, we anticipate near-normal rainfall throughout the RMI for at least the next three months.

Because strong low-level easterly winds are expected to persist across Micronesia and the equatorial Pacific, the sea level should remain higher than normal and may rise further in the RMI and at other locations in Micronesia. Higher-than-normal sea level will expose the atolls of the RMI to a heightened risk of coastal inundation, especially during late November 2011 through February 2012, when enhanced trade winds and the extra-tropical low pressure systems that move eastward from Japan are two sources of large swell that episodically impact the atolls of the RMI. Any large wave event (> 12 ft) coupled with higher-than-normal sea level poses an enhanced risk of coastal inundation.

Forecast rainfall for the Republic of the Marshall Islands from October 2011 through September 2012 is as follows:

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

source: UOG-WERI