Pohnpei Vol.14, No.1

Pohnpei State: Most locations within Pohnpei State were slightly wetter than normal during 2007, particularly in the final quarter of the year. The 193.76 inches recorded at the WSO in Kolonia (103% of its normal annual value of 188.76 inches) was the highest amount observed in Pohnpei State during 2007, although the amounts were most certainly higher in the interior of Pohnpei Island where UOG rain gages have measured over 300 inches of rain in each of the years 2004 - 2006. Most of the atolls of Pohnpei State were wet during 2007 including Mwoakilloa, Nukuoro, and Kapingamarangi. The 155.49 inches of rain recorded at Pingelap during 2007 was somewhat drier (87%) than its estimated mean annual rainfall.

High sea levels and strong trade winds associated with La Niña allowed some ocean inundation to occur on Pohnpei Island. The PEAC Center has received reports that wind-whipped choppy waves were splashing water onto the causeway to the airport and eroding the rock and gravel fill on its east side. Brisk trades and high sea levels are typical during La Niña events. Easterly trade winds should continue to dominate the flow in eastern Micronesia for the next several months. These gusty
winds coupled with elevated sea level could lead to a few episodes of minor coastal inundation and coastal erosion, especially at times of the month when the astronomical tidal range is greatest. No typhoons or tropical storms are anticipated to adversely affect Pohnpei State during 2008, although several of the basin’s tropical cyclones may begin as depressions near Pohnpei. These storms will only contribute to the expected abundant rainfall.

* Long term normal is not established for these sites

Climate Outlook: In a climate of enhanced trade winds, the trade-wind trough, and the zonal band of cloudiness associated with it, sharpens. The result is an increase in rainfall on Pohnpei Island and the atolls that lie within the latitude bounded by 4º to 8º N. This is especially true during April and May when Pohnpei Island usually experiences its highest monthly average rainfall. Conversely, atolls near the equator such as Kapingamarangi typically have reduced rainfall during La Niña. Kapingamarangi is one of only a few places in Micronesia where reduction in rainfall over the next 3 to 6 months may cause problems with water supplies (e.g., rain catchments). The PEAC Center strongly recommends that residents of Kapingamarangi continue voluntary water conservation and other technical measures to ensure an adequate supply of potable water for the next 3-6 months.

Easterly trade winds should continue to dominate the flow in eastern Micronesia for the next several months. These gusty winds coupled with elevated sea level could lead to a few episodes of minor coastal inundation and coastal erosion, especially at times of the month when the astronomical tidal range is greatest. No typhoons or tropical storms are anticipated to adversely affect Pohnpei State during 2008, although several of the basin’s tropical cyclones may begin as depressions near Pohnpei. These storms will only contribute to the expected abundant rainfall.

Forecast rainfall for Pohnpei State from February 2008 through January 2009 is as follows:

Pacific ENSO Update

1st Quarter, 2008 Vol. 14 No. 1