Guam/CNMI:  Annual rainfall totals on Guam were close to normal at most locations, with no reported occurrences of widespread damaging events of wind or rain. One noteworthy aspect of Guam ’s weather during 2006 was an extreme month-to-month variation of the rainfall during July through October. This behavior of the rainfall was likely the result of the Madden Julian Oscillation (MJO). The typical manifestation of the MJO in Micronesia is to produce several weeks of wet weather broken by a week or two of hot dry weather. During the last three months of 2006, the rainfall was generally a bit below normal at most Guam locations. The 4th Quarter 2006 rainfall total of 24.56 inches at the WSO was 96% of normal (the combined result of a wet October followed by dry conditions in both November and December). By the time of the writing of this report (late January) persistent dryness since November of 2006 had begun to manifest in lowered stream flows and the onset of wildfires in the south. Strong trade winds and hazardous surf occurred almost daily for all of January 2007.

The 2006 annual rainfall totals at stations in the CNMI were among the driest in all of Micronesia. The annual total of 56.84 inches at Tinian was the lowest annual total at any recording location in Micronesia , and it was also the lowest rainfall in terms of percent of normal (68%) throughout Micronesia during 2006. The 4th Quarter of 2006 was dry for all three months. On Rota, a very wet October helped to boost annual totals closer to normal than at other islands, and the 4th Quarter total of 31.72 inches was 118% of normal. Saipan was also was drier than normal throughout most of 2006. The SIA 2006 annual total of 65.52 inches was 85% of normal. The 14.99 inches of rain at the SIA during October was the wettest monthly total for all of 2006. Only one other month (July) had over 10 inches, and six months had rainfall totals less than five inches!

For an historical look at how the SOI relates to Guam rainfall, click here.

Guam and CNMI Rainfall Summary 4th Quarter 2006

Climate Outlook: Below normal rainfall is anticipated throughout all of Guam and the CNMI for the first six months of 2007. Island residents are urged to participate in voluntary water conservation measures, and to undertake low-cost repairs and maintenance of the means of obtaining drinking water. If extreme dry conditions develop in the next 3 to 6 months, a more serious effort may be required to ensure adequate water supplies for all islanders. The magnitude of the dry conditions expected for the next 6 months is not anticipated to be as extreme as the dry conditions experienced in the first 6 months of 1983, 1992, or 1998. Most locations are expected to receive 60% to 70% of the rainfall normally expected during the first six months of 2007. However, month-to-month variations in rainfall patterns (which are unpredictable) may cause any location to experience less than half of normal rainfall during any one or two of the months from January through June of 2007. The risk of wildfires will be high beginning in late January through June. Residents are urged to clear away brush and loose combustible materials located near their homes. During the record drought of the dry season of 1998, nearly 12% of Guam ’s land area was scorched by wildfires.

Predicted rainfall for Guam and the CNMI from February 2007 through January 2008 is as follows:

source: UOG-WERI