Pacific ENSO Update
1st Quarter, 2005 Vol. 11 No. 1
Guam/CNMI: Rainfall on Guam during 2004 was excessive. The total rainfall of 139.32 inches at the Guam International Airport (GIA) was well above normal (153%). This was the 2nd wettest year in a time series of rainfall on Guam that extends back to 1950. 2004’s total just surpasses the annual total of 139.10 inches recorded there in 2002, and is exceeded only by the 141.12 inches recorded there in 1976. Guam’s summer rainy season (June through October) was very wet, with enormous month-to-month variation. Beginning in September, however, and continuing into January 2005, Guam has become increasingly dry. The rainfall for October, November, and December at the GIA was 9.86 inches (82%), 6.46 inches (79%), and 9.89 inches (82%) respectively. The total of 19.59 inches was 76% of normal for the 3-month period. At Andersen Air Force Base (AAFB), the rainfall for October, November, and December was 9.57 inches (74%), 9.94 inches (110%), and 4.48 inches (75%) respectively, amounting to 86% of normal for the 3-month period. During the latter half of January 2005, wildfires in Guam’s grasslands have been occurring almost daily. Based on the gradual demise of weak El Niño conditions during 2005, conditions are anticipated to be drier than normal for Guam through the upcoming dry season and into the onset of the summer rainy season.
Two typhoons adversely affected Guam during 2004: Tingting and Chaba. During June 27-28, Typhoon Tingting produced extraordinary amounts of rainfall. 24-hour rainfall totals exceeded 20 inches at many locations. Flooding was extensive, and combined with mudslides caused much property damage. There were 7 deaths attributable to the high surf produced by Tingting. On the night of August 21, Typhoon Chaba passed between Rota and Tinian. Damage to property and vegetation was extensive on these islands. On Guam, Chaba produced heavy rains with a peak 24-hour total of 9.05 inches at the GIA. Westerly winds exceeded typhoon force in gusts on much of the northern half of the island. Fortunately, Guam narrowly escaped the brunt of Typhoon Chaba, and only minor property damage was reported there.
The distribution of rainfall in the CNMI during 2004 was similar to that on Guam: an extraordinarily wet June, a dry July, an extraordinarily wet August, followed by drier than normal conditions in September and October. Rainfall on Saipan during November and December exceeded that on Guam based on heavy rains from passing tropical disturbances that by chance produced more rain on Saipan than on Guam. Typhoon Tingting contributed to the excessive rainfall total during June, and Typhoon Chaba contributed to the excessive rainfall total during August. Typhoon Chaba was a major disaster for the island of Rota, and to a lesser extent for Tinian and Saipan.
The rainfall for October, November, and December at the Saipan International Airport (SIA) was 5.76 inches (53%), 13.10 inches (226%), and 7.58 inches (197%) respectively, amounting to 129% of normal for the 3-month period. The 2004 annual total of 104.88 inches at SIA was well above normal (142%). The 2004 annual total of 115.65 inches at Capitol Hill was also well above its normal (136%). The rainfall at Capitol Hill during October, November, and December was 5.73 inches (48%), 12.02 inches (165%), and 6.56 inches (137%), respectively.
Rainfall amounts for June, July, August, September, and October at the Tinian Airport were 18.80 inches (324%), 1.71 inches (19%), 37.85 inches (303%), 9.16 inches (68%), and 9.16 inches respectively, amounting to 145% of normal for the 5-month period. The 37.85 inches of rainfall at the Tinian Airport during August is an all-time record. On the night of 22 August, Typhoon Chaba passed to the south of Tinian. Rainfall during the two-day period of August 22 through August 23 was 9.88 inches. The peak wind gust recorded at the Tinian Aiport during Chaba was 81 mph.
The 2004 annual rainfall total of 118.84 inches at the Rota Airport was well above normal (125%). Rainfall amounts for October, November, and December at the Rota Airport were 8.53 inches (67%), 9.65 inches (112%), and 3.89 inches (68%) respectively, amounting to 82% of normal for the 3-month period. On the night of August 22, the center of Typhoon Chaba passed just to the north of Rota, placing that island in its eye wall and highest wind speeds. Data recently retrieved from the TRMM-sponsored rain gage network at the Rota Resort and Country Club indicates that rainfall during Typhoon Chaba was far greater there than at the Rota Airport. A two-day total of 16.89 inches occurred at the resort (with a maximum one-hour total of 4.25 inches), whereas only 9.60 inches was recorded at the Rota Airport during the same time period.
With the demise of weak El Niño conditions in 2005, the threat of a typhoon for Guam and the CNMI during the upcoming year is expected to be near normal. During an average year, three or four tropical storms and one or two typhoons pass within 200 miles of any location. The odds of typhoon force winds (or greater) at any given location on Guam or in the CNMI during any given year are approximately 1 in 7. Dangerous surf from a typhoon does not require that the typhoon pass close to any location, so it is certain that at least one episode of dangerous typhoon-generated waves will occur. Every year several lives are lost due to hazardous surf.
Based on the gradual demise of weak El Niño conditions during 2005, conditions are anticipated to be drier than normal for Guam and the CNMI through the upcoming dry season and into the onset of the summer rainy season.
Predicted rainfall for the Mariana Islands from Feb 2005 through Jan 2006 is as follows: