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Pacific ENSO Update

3rd Quarter, 2011 Vol. 17 No. 3


RMI Flag Republic of the Marshall Islands: The 2 nd half of 2010 was very wet at some locations in the RMI. Wet conditions continued during the first three months of 2011, and then drier conditions prevailed in the 2 nd quarter of 2011. Overall, the wet conditions of the first quarter of 2011 outweighed the dry conditions of the 2nd quarter. The 6-month 2011 first half rainfall totals were thus above normal at most recording locations. The long-term climate records at Kwajalein and at Majuro (which begin in the early 1950s) show a long slow decline of mean annual rainfall that is statistically significant. At the WSO Majuro, the downward trend of annual rainfall is such that there is a loss of nearly 20 inches of annual rainfall during the 2000s versus the 1950s. At Kwajalein, the loss of annual rainfall over the same 6-decade time period is approximately 14 inches. The recent wet conditions over the past year have done little to affect the long-term trend, and appear as a small upward fluctuation in an otherwise downward trending time series (Figure 2 below).

 

Figure 2. Rainfall time series at Kwajalein from 1953 to present. Values plotted are a 12-month running average of the monthly rainfall. Note the steady long-term decline, and the pronounced fluctuations that are to a large extent related to ENSO. The recent wet conditions are a relatively small upward spike in the time series. The Majuro time series (not shown) is similar.

 

The recent “RMI Big Wet” was accompanied by some unusual weather events noted on the web site of the Kwajalein Reagan Test Site weather station, now operated by Atmospheric Technology Services Company (ATSC)/Reagan Test Site (RTS) (http://rts-wx.com/). An article entitled, “The Hunt for Wet October” provides details on the very extreme monthly rainfall experience during October 2010. Another article entitled, “Recent Thunderstorm Rattles Island”, describes an intense thunderstorm that affected Kwajalein on the 30 th of January 2011. Frequent cloud to ground lightning (as noted in the latter article) is rare in the maritime tropical regions, primarily the result of land-ocean differences in suspended aerosols and atmospheric stability, both of which act to increase the lightning frequency in continental versus maritime thunderstorms. The cold dry upper atmospheric conditions in TUTT cells are known to enhance the lightning production of thunderstorms that form in association with them. The 30 January 2011 Kwajalein lightning event, however, was not associated with a TUTT cell, and looked rather unremarkable in satellite imagery. The ATSC article takes a good stab at explaining this unusual lightning event in terms of favorable upper level winds allowing long-lived convection. It also provides other useful lightning facts.

Republic of the Marshall Islands Rainfall Summary 2nd Quarter and 1st Half 2011

Station   April May June 2nd Qtr
1st Half
RMI Central and Southern Atolls
Majuro WSO
Rainfall (inches)
3.15
12.60
10.63
26.38
63.35
% of Normal
31%
113%
92%
80%
113%
Arno
Rainfall (inches)
3.92
11.44
8.48
23.84
65.06
% of Normal
38%
102%
73%
72%
111%
Laura
Rainfall (inches)
1.30
16.21
12.04
29.55
60.18
% of Normal
13%
145%
104%
89%
108%
Alinglaplap
Rainfall (inches)
2.60
13.46
10.99
27.05
72.02
% of Normal
29%
127%
104%
90%
152%
Jaluit
Rainfall (inches)
8.39
11.34
10.74
30.47
61.81
% of Normal
82%
101%
93%
92%
111%
RMI Northern Atolls
Kwajalein
Rainfall (inches)
3.76
7.83
8.38
19.97
48.48
% of Normal
50%
78%
87%
74%
124%
Wotje
Rainfall (inches)
3.92
6.72
5.54
16.18
32.33
% of Normal
55%
71%
61%
63%
88%


Climate Outlook: A normally active monsoon trough in the western North Pacific, and the typical distribution of deep convection in the trade wind trough across the RMI should couple to provide near normal to above normal rainfall for at least the next few months at most locations. In the current ENSO-neutral climate state, there are no strong signals for either very wet or very dry conditions.

Forecast rainfall for the Republic of the Marshall Islands from July 2011 through June 2012 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 
July - September 2010
100%
(36.32 inches)
110%
(39.95 inches)
100%
(32.48 inches)

October - December 2010

100%
110%
110%
January - March 2011
100%
100%
100%
April - June 2011
110%
100%
100%

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

source: UOG-WERI



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Page Last Modified: August 09 2011 02:01:38 GMT

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