Pacific ENSO Update

1st Quarter, 2008 Vol. 14 No. 1

FSM Flag Federated States of Micronesia

Chuuk State: Amounts of rainfall during the calendar year 2007 were slightly drier than normal throughout Chuuk State, with the northern atolls of Fananu Onoun and Piis Panew being the driest. The 126.64 inches of annual rainfall at the WSO on Weno Island was 94% of normal, and was one of the higher values of rainfall in Chuuk State for the year. Only Ta and Losap, in the southern and northern Mortlock Islands, respectively, recorded more rainfall during 2007 than the WSO. While weather conditions were generally tranquil, persistent trade winds and high surf contributed to substantial sea inundation on many of the atolls and coastal areas of Chuuk Lagoon early in 2007, causing damage to taro patches and other staple food plants such as breadfruit trees. From early December 2007 through mid-January 2008, high astronomical tides and strong trade winds combined with already elevated sea levels (associated with La Niña) to produce more coastal flooding and inundation in Chuuk and Pohnpeistates — damaging roads, taro patches and property.

Chuuk State Rainfall Summary 4th Quarter 2007

Station   Oct. Nov. Dec. 4th Qtr Annual
Chuuk WSO Rainfall (inches)
8.68
12.76
13.84
35.28
126.64
% of Normal
62%
119%
127%
99%
95%

Piis Panew*

Rainfall (inches)
3.92
13.92
11.70
29.54
76.31
Xavier HS Rainfall (inches)
7.35
13.40
13.84**
34.59**
11.64**

Lukunoch*

 Rainfall (inches)

9.85
12.68
11.79
34.32
117.08
Ettal* Rainfall (inches)
7.62
13.00
18.45
39.10
125.24

Ta*

Rainfall (inches)
6.87
18.18
23.06
48.11
156.51

Fananu*

Rainfall (inches)
9.34
13.19
9.28
31.81
100.19
Onoun* Rainfall (inches)
12.66
16.29
10.78
39.73
112.25

Losap*

Rainfall (inches)
10.39
17.28
11.72
39.39
130.17

Nama*

Rainfall (inches)
7.05
15.48
15.78
38.31
124.20

Polowat

Rainfall (inches)
3.02
12.34
4.51
19.87
106.31
* Long term normal is not established for these sites
** Estimated

Climate Outlook: Gusty easterly trade winds should continue to dominate the flow throughout Micronesia for the next three months. Higher than normal sea level coupled with high surf is likely to cause more inundation events in Chuuk Lagoon and other low islands in Chuuk State. These conditions are possible through April of 2008, after which the trade winds normally weaken. Rainfall should be near normal throughout Chuuk State for all of 2008. From August through December, several tropical cyclones of the western North Pacific basin will begin their lives in Chuuk State as depressions, bringing episodes of heavy showers across Chuuk State before they move northwestward. One or two occurrences of gale-force wind associated with a tropical cyclone may affect Chuuk Lagoon or atolls to the north during 2008, representing a normal risk. Also, there is a higher likelihood than during 2007 for a substantial rain event (10 to 15 inches in one day) that could cause slope failures and mudslides on the high islands of Chuuk Lagoon. This also represents a normal risk of such an event.

Forecast rainfall for Chuuk State from February 2008 through January 2009 is as follows:

Inclusive Period
% of Long-Term Average Rainfall /
Forecast Rainfall (inches)
Chuuk Lagoon, and Northern Mortlocks
Polowat
Northern Atolls

Southern
Mortlocks
February - April 2008
 110%
(29.13 inches)
100%
100%
120%
May - July 2008
120%
110%
100%
120%
August - October 2008
110%
95%
120%
100%
Nov 2008 - Jan 2009
100%
100%
100%
100%
Forecast rainfall quantities represent BEST ESTIMATES given the probabalistic forecast for each particular season and station.

source: UOG-WERI