Pacific ENSO Update

1st Quarter, 2006 Vol. 12 No. 1

FSM Flag Federated States of Micronesia

Pohnpei State:  Rainfall was abundant throughout all of Pohnpei State during 2005. On Pohnpei Island, the 2005 annual totals were near or above 200 inches at many locations around the coastal perimeter of the island. The annual total of 217.87 inches at Palikir (on the northwest side of Pohnpei Island) was the highest officially recorded value in all of Micronesia during 2005. Unofficially, the experimental UOG/CSP rain gage on top of Nahna Laud recorded over 300 inches of rain during 2005. The enormous amount of rainfall at Palikir was actually near normal at 107%. The annual rainfall total for 2005 at the Pohnpei WSO (on the north side of Pohnpei Island) was 191.05 inches (101%). On the atolls of Pohnpei State, the rainfall during 2005 was abundant, and exceeded 150 inches at all recording locations. Kapingamarangi has been wetter than normal for a long time, and continued to be very wet through its dry season and the final quarter of 2005. The current shift of the climate to weak La Niña may finally force an end to the long period of well-above normal rainfall at Kapingamarangi.

Pohnpei Rainfall Summary 4th Quarter 2005
Station   Oct. Nov. Dec. Total 2005
Pohnpei WSO Rainfall (inches) 12.17 13.85 14.94 40.96 191.05
% of Normal 73% 88% 98% 86% 101%
Palikir* Rainfall (inches) 16.71 15.74 15.22 47.67 217.87
% of Normal         107%**
Nukuoro Rainfall (inches) 9.08 7.90 14.26 31.24 175.29
% of Normal 84% 66% 119% 90% 117%
Pingelap Rainfall (inches) 10.97 11.78 11.80 34.55 167.82
% of Normal 74% 83% 88% 81% 94%
Mwokilloa* Rainfall (inches) 7.88 12.08 11.68 31.64 154.64
Kapingamarangi Rainfall (inches) 9.64 7.49 10.91 28.04 152.53
% of Normal 200% 91% 125% 129% 139%
* Long term normal is not established for these sites ** Annual mean based on PRISM


Climate Outlook:

During La Niña years, the tropical cyclones of the western North Pacific form to the west and north of normal. If weak La Niña conditions persist through much of 2006, then the risk of a damaging tropical storm or typhoon would be very unlikely at any island in Pohnpei State during 2006. The very early stages of developing tropical cyclones may bring some episodes of heavy rain to Pohnpei, but these systems should not become tropical storms or typhoons until they are well away from Pohnpei.

Based on weak La Niña conditions during the first half of 2006, rainfall at Pohnpei Island and the atolls of Pohnpei State should be wetter than normal for most months of the year, and especially in the spring (late March through early June) when the trade-wind trough becomes established in the region. The only exception to this is Kapingamarangi where La Niña-related weather patterns may finally shift heavy rainfall away from this island.

Predicted rainfall for Pohnpei State from January 2006 through December 2006 is as follows:

Inclusive Period

% of Long-Term Average
Pohnpei Islands and Atolls
Kapingamarangi
Jan – Mar 2005 125% 100%
Apr – Jun 2006 130% 100%
Jul – Sep 2006 110% 95%
Oct – Dec 2006 110% 90%
Source: UOG-WERI