Hawaiian Winter Rainfall and its Relation to the Southern Oscillation

Abstract

Regression analyses revealed significant variability during the winter months in the relationship between Hawaiian winter rainfall and the Southern Oscillation. Examination of daily surface and upper air charts indicated that the variability during winter is a consequence of a marked change from December to January in the upper tropospheric circulation pattern over the central subtropical North Pacific. In January and February, positive 200 mb geopotential height anomalies over the Hawaiian Islands are indicative of an intensification and eastward propagation of the western North Pacific subtropical ridge. Consequently, the storm track is north and cast of Hawaii and such months are dry in the Hawaiian Islands. However, in December, positive 200 mb geopotential height anomalies over Hawaii are not necessarily indicative of such an upper tropospheric circulation and such Decembers need not be dry. Therefore, even though the December through February Southern Oscillation Index is significantly correlated with monthly 200 mb geopotential heights over the Hawaiian Islands, only during January and February is it positively correlated with contemporaneous Hawaiian rainfall.