Skip Navigation Links weather.gov 
NOAA logo-Select to go to the NOAA homepage National Weather Service Forecast Office   Select to go to the NWS homepage
Pacific ENSO Applications Climate Center
banner piece
  banner piece
Local forecast by
"City, St" or Zip Code
Pacific ENSO Update

3rd Quarter, 2009 Vol. 15 No. 3


Guam and CNMI text Guam/CNMI:  The first half of 2009 was generally drier than normal throughout Guam. Persistent trade winds accompanied especially dry conditions at some Guam locations during the 2nd Quarter months. Despite dry conditions, the weather remained just wet enough to sustain southern Guam’s drinking water sources at the Ugum River pumping stations and the Fena Reservoir, and to reduce the number of dry season grass fires. The rainfall totals during the first half of 2009 were approximately 20-25 inches at all recording locations, ranging from 19.25 inches at WFO Guam to 26.60 inches at the head of the Ugum watershed in the southern mountains. The weather on Guam during the first half of 2009 continued to be mundane, as it has been for much of the past three years, with no unusually heavy rains or strong winds.

The 2nd Quarter 2009 and 1st half of 2009 rainfall totals in the CNMI were generally drier than normal, with six-month totals near 25 inches, similar to Guam. However, a particularly wet June – with 8.25 inches and 8.32 inches recorded at the Saipan International Airport and Rota Airport, respectively – inflated seasonal rainfall totals, masking the true extent of persistent dryness. For the first time in recent history, it was noted that Donni Spring in the central Saipan highlands completely dried up; the combination of low rainfall and new wells in the area were thought to have contributed to this. The weather continued its long period of tranquility throughout the CNMI during the first half of 2009 with no unusually heavy rains or strong winds, some brief periods of heavy showers in June notwithstanding.

Guam and CNMI Rainfall Summary 2nd Quarter 2009

Station   April May June 2nd Qtr
1st Half
Guam
Guam Intl. Airport (WFO)
Rainfall (inches)
3.30
3.57
4.58
11.18
20.67
% of Normal
77%
59%
71%
68%
75%
Anderson AFB
Rainfall (inches)
3.40
2.66
3.50
9.56
19.54
% of Normal
70%
40%
55%
54%
60%
University of Guam
Rainfall (inches)
2.04
1.77
5.43
9.24
19.25
% of Normal
52%
29%
84%
56%
70%
Dedado (Ypapao)*
Rainfall (inches)
2.57
4.08
4.11
10.76
22.72
% of AAFB
66%
67%
64%
65%
82%
Ugum Watershed **
Rainfall (inches)
4.96
5.29
3.86
14.11
26.60
% of WSMO
102%
87%
60%
81%
82%
Sinajaña***
Rainfall (inches)
2.37
5.08
6.34
13.79
25.02
% of WFO
61%
84%
98%
84%
91%
Commonwealth of the Northern Mariana Islands
Saipan Intl. Airport
Rainfall (inches)
1.25
2.38
8.25
11.88
25.83
% of Normal
43%
52%
170%
96%
128%
Capital Hill
Rainfall (inches)
0.97
3.18
6.61
10.76
20.74
% of Normal
28%
58%
114%
73%
85%
Tinian Airport
Rainfall (inches)
1.46
4.96
5.20
11.62
17.62
% of Normal
42%
90
90
79%
73%
Rota Airport
Rainfall (inches)
2.55
2.24
8.32
13.11
27.88
% of Normal
56%
35%
134%
77%
91%
* % of normal for Dededo is with respect to AAFB.
** % of normal for Ugum is with respect to WSMO Finigayan (now closed).
*** % of normal for Sinajaña is with respect to WFO Tiyan (GIA).

Climate Outlook: The 2009 dry season on Guam and in the CNMI persisted through June. In early July, the monsoon trough developed normally across Micronesia, and the rainy season commenced on Guam and in the CNMI. With El Niño conditions now developing in the Pacific Basin, the tranquil weather of the past three years may be coming to an end. All islands should have abundant rainfall through the end of 2009 and may see an increase in the frequency of heavy rainfall events (i.e., 2 inches or more in 24 hours), with high month-to-month variability. Thereafter, the rainfall amounts will depend on the evolution of El Niño: if El Niño persists into the first half of 2010, near normal rainfall will continue, but if El Niño ends in the first half of next year, tranquil and dry conditions will resume. Very dry conditions in Guam and throughout Micronesia are almost always experienced after a strong El Niño, and sometimes follow a weak or moderate El Niño as well.

El Niño also brings an increased risk of the damaging effects from a passing tropical storm or typhoon, especially later in the year. Damaging effects from tropical cyclones include heavy rainfall, high winds, and dangerously high surf. From August through December 2008, Guam and the CNMI can expect to be threatened by 2 or 3 tropical cyclones that will produces gales and hazardous seas in the island waters. The odds of damaging winds (60 mph or higher) from a severe tropical storm or a typhoon on Guam and for each island of the CNMI will be 20 to 25% for the remainder of 2009, which is roughly two to three times the normal level of risk.

Predicted rainfall for Guam and the Mariana Islands from July 2009 through June 2010 is as follows:

Inclusive Period

% of Long-Term Average Rainfall /
Forecast Rainfall (inches)
Guam/Rota
Saipan/Tinian
July – September 2009
(Heart of Next Rainy Season)
110%
(41.53 inches)
100%
(31.74 inches)
October – December 2009
(End of Next Rainy Season)
120%
120%
January – March 2010
(Onset of Next Dry Season)
90%*
90%*
April – June 2010
(End of Dry Season)
90%*
90%*

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: June 01 2010 22:10:28 GMT

Disclaimer
Credits
Glossary

Privacy Policy
About Us
Career Opportunities