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Pacific ENSO Update

1st Quarter, 2012 Vol. 18 No. 1


Guam and CNMI text Guam/CNMI: Throughout Guam and the CNMI, the weather and climate of 2011 was not quite so dull and uneventful as it was during 2010. As La Niña relaxed during the first half of the year, and the state of the climate became ENSO-neutral for the summer, some weak to moderate episodes of the western Pacific monsoon occurred. These brought periods of widespread heavy rain showers and thunderstorms, and also a few episodes of high surf on the western sides of the islands. Rainfall throughout the region was generally above normal, especially during July through October. During the night of 02 September, up to seven inches of rain fell across mid-Guam, and the 7.02 inches of rainfall recorded at the UOG was the heaviest daily rainfall total there since August 2004. When La Niña returned in the final months of 2011, the weather and climate of the region returned to its dull and uneventful state. Trade winds returned to dominate the weather, tropical cyclone activity shifted far to the west, and rainfall was near normal.

The dry season is now underway on Guam and in the CNMI. The trade winds are well established, and trade wind showers and some weak shear line passages have kept conditions somewhat wet. The cool wet weather has kept the grasslands green, and helped to prevent the usual upswing in dry season brush fires.

Guam and CNMI Rainfall Summary 4th Quarter 2011

Station   Oct Nov Dec 4th Qtr Annual
Guam
Guam Intl. Airport (WFO)
Rainfall (inches)
15.45
6.14
5.24
26.83
114.59
% of Normal
128%
75%
97%
107%
126%
Anderson AFB
Rainfall (inches)
11.54
8.09
6.12
25.75
110.74
% of Normal
90%
89%
103%
92%
113%
Dedado (Ypapao)
Rainfall (inches)
11.94
8.33
7.02
27.29
119.09
% of Normal
93%
92%
118%
98%
121%
Ugum Watershed
Rainfall (inches)
12.61
8.40
5.43
26.44
119.08
% of Normal
134%
81%
86%
95%
121%
Sinajaña
Rainfall (inches)
19.42
6.24
5.53
31.19
121.48
% of Normal
161%
76%
103%
122%
134%
Commonwealth of the Northern Mariana Islands
Saipan Intl. Airport
Rainfall (inches)
17.63
3.22
4.65
25.50
82.59
% of Normal
157%
53%
116%
119%
107%
Capital Hill
Rainfall (inches)
16.34
2.81
6.00
25.15
104.81
% of Normal
136%
38%
125%
104%
126%
Tinian Airport
Rainfall (inches)
9.70
2.66
2.48
14.84
85.10
% of Normal
81%
36%
52%
62%
102%
Rota Airport
Rainfall (inches)
14.37
6.21
5.59
26.17
114.70
% of Normal
113%
72%
98%
97%
121%

Climate Outlook: Guam and the CNMI are now entering the heart of their dry season. March is typically the driest month of the year in this region, with 3 to 4 inches of rainfall on Guam and only about 2 to 3 inches on Saipan. The evolution of the state of the climate system during the first half of 2012 is anticipated to be somewhat similar to what it was during the first half of 2011: La Niña conditions falling back toward ENSO-neutral. During years that begin in La Niña and then transition towards ENSO-neutral, the spring rainfall on Guam and in the CNMI is typically near normal or above normal. Tropical cyclone activity is likely to see a delay in the basin and in the region, but during July or August, the monsoon should once again bring abundant rainfall and an upswing of tropical cyclone formations to near-normal levels. There has not been a strong monsoon on Guam, the CNMI, or anywhere in Micronesia since 2004! The reason for this is an unusual inter-decadal shift in ENSO behavior since 1998 that has resulted in a climate state more strongly dominated by La Niña with weaker El Niño events (e.g., 2006 and 2009). It is not known when again there will be a return to a period dominated by El Niño, with strong monsoons and many tropical cyclones.

Predicted rainfall for Guam and the Mariana Islands from January 2012 through December 2012 is as follows:

Inclusive Period

% of Long-Term Average Rainfall /
Forecast Rainfall (inches)
Guam/Rota
Saipan/Tinian
January – March 2012
(1st Half of Dry Season)
120%
(13.40 inches)
100%
(7.74 inches)
April – June 2012
(2nd Half of Dry Season)
120%
100%
July – September 2012
(Onset of Next Rainy Season)
120%
120%
October – December 2012
(2nd Half of Next Rainy Season)
110%
100%

Forecast rainfall quantities represent BEST ESTIMATES given the probabalistic forecast for each particular season and station.

source: UOG-WERI



Pacific ENSO Applications Climate (PEAC) Center
c/o NOAA NWS - Weather Forecast Office Honolulu
2525 Correa Road, suite 250
Honolulu, HI 96822
(808) 956-2324

Web Master's email: peac@noaa.gov
Page Last Modified: March 22 2012 05:05:11 GMT

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