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Pacific ENSO Update

3rd Quarter, 2012 Vol. 18 No. 3


Guam and CNMI text Guam/CNMI: Throughout Guam and the CNMI, the rainfall during the first half of 2012 was generally near normal, ranging from a dry 81% of average at AAFB to a wetter 116% of average at Tinian. At most locations on Guam and in the CNMI, the rainfall totals during the first half of 2012 were nearly ten inches less than during the first half of 2011. April 2012 was very dry throughout the region, while May 2012 was wet. During the third week of May, TS Sanvu passed just to the southwest of Guam and deposited upwards of four inches of rain island-wide over three or four days. This represented over half the May total. Saipan’s relatively modest six-month rainfall total of 17.60 inches (90%) was the lowest reading in the region. The six-month reading of 37.30 inches at the Ugum Watershed site in Guam’s southern mountains was the highest reading in the region. No extraordinary short period rainfall events were experienced during the first half of 2012, with zero occurrences of two inches or more rainfall in 24 hours at both Guam WSO and Saipan International Airport. During July, the weather became tranquil across Guam and the CNMI, and rainfall amounts fell below normal. The southwest monsoon has so far failed to reach Guam, and tropical cyclone activity (busy in the western Pacific basin in May and June) became unusually quiet during July, with one weak tropical storm (Khanun) forming well northwest of the islands. At the time of this writing (July 24) another typhoon (Vicente) had just made landfall west of Hong Kong.

Dry conditions at Saipan through April of 2012 resulted in desiccated vegetation, brown grass, and dusty roadsides. On Guam, there was enough rain to keep lawns green, and wildfires were infrequent and relatively small. The rainy season seemed to be off to a good start with a wet May and June, but during July the rains let up, and the islands await the start of persistent heavier rains normally seen during the heart of the rainy season.

Guam and CNMI Rainfall Summary 2nd Quarter and 1st Half 2012

Station   April May June 2nd Qtr
1st Half
Guam
Guam Intl. Airport (WFO)
Rainfall (inches)
3.05
7.63
6.63
17.31
31.11
% of Normal
78%
126%
102%
105%
113%
Anderson AFB
Rainfall (inches)
1.21
8.46
5.41
15.08
26.60
% of Normal
25%
128%
85%
85%
81%
Dedado (Ypapao)
Rainfall (inches)
1.42
8.88
6.15
16.45
33.46
% of Normal
29%
135%
97%
92%
102%
Ugum Watershed
Rainfall (inches)
2.57
7.56
10.86
20.99
37.30
% of Normal
53%
106%
167%
115%
112%
Sinajaña
Rainfall (inches)
3.22
9.44
6.46
19.12
31.51
% of Normal
81%
157%
101%
117%
114%
Commonwealth of the Northern Mariana Islands
Saipan Intl. Airport
Rainfall (inches)
0.92
3.96
4.26
9.14
17.60
% of Normal
33%
90%
92%
79%
90%
Capitol Hill
Rainfall (inches)
1.15
11.82
5.37
18.34
25.46
% of Normal
33%
215%
93%
124%
105%
Tinian Airport
Rainfall (inches)
2.44
9.78
4.47
16.69
28.18
% of Normal
70%
178%
77%
113%
116%
Rota Airport
Rainfall (inches)
1.64
9.45
6.62
17.71
26.74
% of Normal
36%
149%
100%
104%
87%

Climate Outlook: Guam and the CNMI depend on tropical cyclone activity and the southwest monsoon for much of their rainy season rainfall. As El Niño builds in the Pacific basin, we anticipate that the monsoon will eventually be invigorated by at least early August, and reach Guam and the CNMI. At least two or three week-long episodes of the southwest monsoon should sweep across Guam and the CNMI sometime from now through October. Also, two or three tropical storms and one typhoon are forecasted to pass within 180 NM of Guam and Saipan, with the greatest cyclone risk later in the year (October through December). This is near normal tropical cyclone activity for the complete historical record. Because recent years have had very low tropical cyclone activity in the western North Pacific basin, there has been a dramatic reduction in the numbers of tropical cyclones affecting Guam and the CNMI. A normal number of cyclones passing through regional waters will likely be perceived as unusually active. A degree of complacency sets-in when the weather has been so pleasant and uneventful for so long.

Predicted rainfall for Guam and the Mariana Islands from July 2012 through June 2013 is as follows:

Inclusive Period

% of Long-Term Average Rainfall /
Forecast Rainfall (inches)
Guam/Rota
Saipan/Tinian
July – September 2012
(Heart of Rainy Season)
120%
(45.30 inches)
120%
(40.92 inches)
October – December 2012
(End of Next Rainy Season)
120%*
120%*
January – March 2013
(Onset of Next Dry Season)
90%
80%
April – June 2013
(2nd Half of Next Dry Season)
80%**
70%**

* Value based on high likelihood of a nearby typhoon.
** Value based on the typical dryness after an El Niño event.

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
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2525 Correa Road, suite 250
Honolulu, HI 96822
(808) 956-2324

Web Master's email: peac@noaa.gov
Page Last Modified: December 12 2012 23:18:29 GMT

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