Pacific ENSO Update

4th Quarter, 2005 Vol. 11 No. 4


With few exceptions, the weather and climate of Micronesia through September 2005 has been unremarkable. Abundant (but not excessive) rainfall occurred at most islands. Other than very dry conditions throughout most of Micronesia in February, there were few noteworthy monthly anomalies, and very few noteworthy short-term extreme events. The number of tropical cyclones in the western North Pacific basin has been lower than average, and tropical cyclone formation was north and west of normal, keeping most of the tropical storms and typhoons away from Micronesia. Typhoon Nabi affected Saipan on the last day of August with high winds and heavy rain. Damage was relatively light, and the island was back to normal within a few days of the passage of this tropical cyclone. In American Samoa, rainfall has been above normal throughout the year with the most dramatic weather events occurring in February. During February, several hurricanes passed near American Samoa with Hurricane Olaf causing substantial damage.

According to the U.S. Climate Prediction Center (CPC), the climate of the tropical Pacific is now in ENSO Neutral, and has been in this state since El Niņo conditions abated in early 2005. The islands of Micronesia are typically drier than normal in the first few months of the year following an El Niņo. Also, during the entire year that follows an El Niņo event, the month-to-month variability of rainfall is not as great as it is during El Niņo (primarily a result of the westward shift of tropical cyclone activity). During July, August, and September 2005, most of the islands of Micronesia had abundant rainfall (Fig. 1a, 1b). Only some of the islands in the northern portion of the RMI experienced persistent dryness that was considerably less than what is normally expected. 3- month July through September rainfall totals below 80% were experienced only in the northern islands of the RMI, including Kwajalein, Utirik, and Wotje. 3-month July through September rainfall totals in excess of 120% of normal were experienced at islands in several groups: American Samoa (Pago Pago and Aafasou), Palau (Koror), Yap (Woleia), the CNMI (Saipan Capitol Hill and Rota), Guam (only at Andersen Air Force Base), and at some of the atolls of Pohnpei (Nukuoro and Kapingamarangi). The highest rainfall total recorded in Micronesia for the 3rd Quarter (JAS) of 2005 was 59.25 inches at Palikir on Pohnpei Island. The lowest recorded three month rainfall total during the 3rd Quarter of 2005 was 14.27 inches of rain at Wotje, RMI. Abundant (but not excessive) rainfall is anticipated throughout most of Micronesia and American Samoa for the next three to six months. Many of the islands of Micronesia north of 10° North Latitude will soon enter their dry season. Three or four tropical storms may form in the central Caroline Islands in the remaining months of 2005 into January of 2006. One or two of these tropical storms could become a typhoon after moving out of the Caroline Island Group and then threaten Guam, the CNMI, or Yap State. This is normal (see each island summary for the meaning of a "normal" tropical cyclone threat).

The general consensus among international computer climate forecasts is for a continuation of ENSO Neutral conditions for the next six months. For more information, see the CPC EL NIŅO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSION for October.