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Pacific ENSO Update

1st Quarter, 2011 Vol. 17 No. 1


RMI Flag Republic of the Marshall Islands: The RMI is one of the regions of the tropical Pacific basin where the mean annual rainfall exhibits a statistically significant long-term decline. Hawaii is another such region, where, over its 100-year climate record, the rainfall and stream flow has been declining. During 2010, a few months of heavy rainfall pushed the 2010 annual rainfall totals at some of the atolls of the RMI to near normal values. For example, the 138.18 inches experienced at the WSO Majuro was 105% of normal. A dry start to the year at Majuro was overwhelmed by some very wet months, with the 20.86 inches of rain during June the heaviest monthly total of the year. Mili was near normal for the 4th Quarter with 30.07 inches of rain or 98%, but for the entire year, the southernmost atoll was drier than normal. In fact, at most other atolls, the annual rainfall did not go above normal. For example, at Kwajalein, the 2010 annual rainfall of 87.30 inches was 86% of normal. But even there, there were some very high monthly rainfall totals in the second half of the year. During October and November, Kwajalein had 18.56 and 16.97 inches, respectively. In spite of a few months of very heavy rainfall, the 2010 annual totals were below normal at most RMI locations! The northern islands of Utirik and Wotje were well below normal, with only 41% and 48% of normal rainfall, respectively.

Republic of the Marshall Islands Rainfall Summary 4th Quarter 2010

Station   Oct Nov Dec 4th Qtr Annual
RMI Southern and Central Atolls (South of 8°N)
Majuro WSO
Rainfall (inches)
13.18
18.13
11.01
43.32
138.18
% of Normal
95%
142%
93%
110%
105%
Laura
Rainfall (inches)
11.86
13.77
8.54
34.17
110.04
% of Normal
86%
108%
72%
89%
84%
Mili
Rainfall (inches)
12.79
8.95
8.33
30.07
107.82
% of Normal
92%
70%
77%
98%
84%
Arno
Rainfall (inches)
15.48
22.63
6.95
45.06
125.10
% of Normal
112%
177%
59%
117%
95%
Alinglaplap
Rainfall (inches)
16.75
20.40
5.62
42.77
103.06
% of Normal
130%
174%
56%
124%
88%
Jaluit
Rainfall (inches)
5.93
7.15
5.73
18.81
91.40
% of Normal
43%
56%
48%
49%
70%
RMI Northern Atolls (North of 8°N)
Kwajalein
Rainfall (inches)
18.56
16.97
2.96
38.49
87.30
% of Normal
156%
159%
37%
125%
86%
Wotje
Rainfall (inches)
6.56
9.75
1.75
18.06
46.95
% of Normal
58%
96%
23%
62%
48%
Uterik
Rainfall (inches)
11.00
2.93
4.06
17.99
35.95
% of Normal
109%
32%
59%
69%
41%


Climate Outlook: The weather pattern for 2011 should continue to feature widespread easterly low-level winds, tropical cyclones pushed to the west of normal (at least for the first half the year), and a monsoon trough that does not push eastward beyond Chuuk at low latitudes. In this pattern, the trade wind trough dominates the weather of the RMI. During the RMI rainy season (July through December), low pressure systems in the upper atmosphere (i.e., TUTT cells) passing north of the RMI modulate the deep convection, and help to bring bouts of heavy rain showers to the atolls. This was the case during 2010, where a fortuitous set-up of the upper atmospheric wind patterns helped to bring some episodes of very heavy rainfall to many of the atolls. Not counting on the help of unusually favorable upper air flow patterns, and considering the long-term trend of declining rainfall in the RMI, the outlook for 2011 is for near normal to slightly below normal rainfall for most months of 2011 and for the annual total.

Forecast rainfall for the Republic of the Marshall Islands from January 2011 through December 2011 is as follows:

Inclusive Period
% of Long-Term Average Rainfall /
Forecast Rainfall (inches)
South of 6° N
6° N to 8° N
North of 8° N 
January - March 2011
(Dry Season)
95%
(22.21 inches)
90%
(21.04 inches)
85%
(10.77 inches)
April - June 2011
(Onset of Rains)
100%
100%
95%
July - September 2011
(Rainy Season)
100%
100%
100%
October - December 2011
(Start of Dry Season)
100%
100%
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
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2525 Correa Road, suite 250
Honolulu, HI 96822
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Web Master's email: peac@noaa.gov
Page Last Modified: March 01 2011 02:11:47 GMT

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