Pacific ENSO Update

1st Quarter, 2009 Vol. 15 No. 1

FSM Flag Federated States of Micronesia

Pohnpei State: The majority of locations in Pohnpei State had near normal rainfall during 2008. The 189.34 inches recorded at the WSO in Kolonia was 100% of its normal annual value. Other Pohnpei Island locations such as the Airport and Palikir also had near-normal rainfall during 2008. Nukuoro was particularly wet during 2008; its annual total of 211.14 was the highest amount observed in Pohnpei State during 2008, although the amounts were most certainly higher in the interior of Pohnpei Island where rain gages installed by the UOG have measured over 300 inches of rain in each of the years 2004 through 2007. Other atolls of Pohnpei State were either slightly dry (Pingelap and Mwoakilloa) or near normal (Kapingamarangi) during 2008. High sea-levels and strong trade winds associated with the resurgent La Niña allowed some ocean inundation to occur on Pohnpei Island in recent months. The PEAC Center received reports that wind-whipped waves were splashing water over the causeway at the airport and eroding the rock and gravel fill on its east side. Brisk trades and high sea levels are typical during La Niña. Because of its protective fringing reef, the high surf event of December 2008 was not as destructive on Pohnpei Island as at other atolls and islands with more exposure.

Pohnpei Rainfall Summary 4th Quarter 2008

Station   Oct. Nov. Dec. 4th Qtr
Annual
Pohnpei Island
Pohnpei WSO
Rainfall (inches)
20.41
16.61
9.58
46.63
189.34
% of Normal
122%
106%
63%
98%
100%
Palikir
Rainfall (inches)
19.95
18.16
10.84
48.95
201.12
% of Normal
110%
107%
66%
95%
99%
Kolonia Airport
Rainfall (inches)
18.73
12.12
7.42
38.27
161.74
% of Normal
137%
94%
59%
98%
104%
Atolls of Pohnpei State
Nukuoro
Rainfall (inches)
18.04
17.02
9.38
44.44
211.14
% of Normal
168%
142%
78%
128%
141%
Pingelap
Rainfall (inches)
11.38
12.57%
7.51%
31.46
157.36
% of Normal
N/A
N/A
N/A
74%
89%
Mwokilloa
Rainfall (inches)
9.61
11.43
14.48
35.52
144.43
% of Normal
N/A
N/A
N/A
76%
110%
Kapingamarangi
Rainfall (inches)
6.38
3.27
10.88
20.53
108.39
% of Normal
132%
40%
124%
94%
99%
* Long term normal is not established for these sites

Climate Outlook: In a climate of enhanced trade winds, such as during La Niña, the trade-wind trough and zonal band of cloudiness associated with it sharpens and increases the rainfall on Pohnpei Island and atolls that lie within the latitude bounds of 4º to 8º N. This is especially true for the months of April and May when Pohnpei Island usually experiences its highest monthly average rainfall. Another month of 30 inches or more (such as May 2008), could be experienced again during any of the months between April and June 2009. Nukuoro recorded particularly high rainfall in this pattern, and will likely see a repeat of high rainfall in the coming months. Easterly trade winds should continue to dominate the flow in eastern Micronesia for the next several months. These gusty winds coupled with elevated sea-level could lead to a few episodes of minor coastal inundation and coastal erosion, especially at times of the month when the astronomical tidal range is greatest. The airport causeway on Pohnpei Island may again have sea water splash across it. No typhoons or tropical storms are anticipated to adversely affect Pohnpei State during 2009, although several of the basin’s tropical cyclones may begin as depressions near Pohnpei. These will only contribute to the expected abundant rainfall.

Forecast rainfall for Pohnpei State from January 2009 through December 2009 is as follows:

Inclusive Period

% of Long-Term Average Rainfall /
Forecast Rainfall (inches)
Pohnpei Islands and Atolls Kapingamarangi
January - March 2009
100%
(36.26 inches)
95%
(34.46 inches)
April - June 2009
125% 100%
July - September 2009
100% 100%
October - December 2009
100% 95%
Forecast rainfall quantities represent BEST ESTIMATES given the probabalistic forecast for each particular season and station.

Source: UOG-WERI