Pacific ENSO Update
3rd Quarter, 2007 Vol. 13 No. 3
Guam/CNMI: The weather on Guam during the first half of 2007 was overall quite dry. The total rainfall for the first half of 2007 was approximately 20 inches at all recording locations (ranging from 16.77 inches at Andersen AFB to 28.55 inches at Ypapao in the north). These amounts, and those elsewhere on the island, were roughly 50 to 70% of the normal rainfall expected during this typically dry half of the year. Wildfires were frequent in March and early April. Fires abated in May after some heavy rainfall, but then recurred in June as hot, dry conditions once again prevailed. On the 8th - 10th of July, the developing Typhoon Man-Yi passed to the southwest of Guam, bringing some heavy showers and southeasterly gales. Winddriven sea salt scorched and browned the vegetation all along the eastern shoreline, with some small branches and loose coconut fronds blown down.
The rainfall totals in the CNMI for the first half of 2007 were generally a few inches higher than those on experienced on Guam. The 3 to 4 inches of rainfall experienced in the CNMI during the passage of Typhoon Kong-Rey in early April (with Guam only getting 0.5 inches) made-up most of this difference. The highest amount of rain recorded in the CNMI during the first half of 2007 was the 26.11 inches at the observing site at Capitol Hill, followed closely by the 25.88 inches recorded at the Saipan International Airport. Though the amounts of rainfall in the CNMI were quite dry when compared with other locations (see Fig. 1a), many locations were actually above normal for the season (see Fig. 1b) because it is normally so very dry at this time of year.
Guam and CNMI Rainfall Summary 2nd Quarter 2007
* % of normal for Dededo is with respect to WSMO Finigayan
** % of normal for Ugum is with respect to WSO Tiyan (GIA)
Climate Outlook: The rainy season on Guam and in the CNMI is off to a slow start. Near normal rains, however, should prevail in the region from August through the late fall as the monsoon circulation of the western North Pacific and tropical cyclone activity should finally begin to affect the western half of Micronesia. Easterly trade winds should continue to dominate the flow in eastern Micronesia (Pohnpei and eastward), and keep rainfall average to slightly below average. Monsoon and storm activity will have more influence in western Micronesia (Chuuk and westward), and these areas will likely see average to slightly above average rainfall. The Marianas will have near average rainfall. The trade winds and sub-surface heating in the western North Pacific will keep sea levels above normal. Tropical cyclone activity is expected to be below normal throughout the entire western North Pacific basin during 2007. From August through the remainder of the year, however, Guam and the CNMI may expect to be threatened by 2 or 3 tropical cyclones that will produces gales and hazardous seas in the island waters. The odds of damaging winds from a typhoon on Guam and for each island of the CNMI will be approximately 10 to 15% for the remainder of the year, which is normal for a non-El Niño year.
Foreacst rainfall for Guam and the CNMI from August 2007 through July 2008 is as follows:
* Forecasts are subject to large error if a typhoon should pass directly over any island!