Impact of the Hawaiian High on Interannual Variations of Winter Precipitation over California

Past investigations have shown that interannual variability in winter precipitation over the western United States is related to large-scale sea level pressure fluctuations. California is adjacent to the North Pacific subtropical high, also known as the Hawaiian high. This study analyzes the relationship between interannual variations of winter precipitation in California and fluctuations in the Hawaiian high's pressure and location. Defining objective indices to characterize the high, it is shown that precipitation in California is significantly anticorrelated with the high's intensity. Precipitation is also shown to decrease as the high shifts southward or eastward. A linear regression model of December-March precipitation averaged over all of California with the pressure and longitude of the high as independent variables explains 43% of the precipitation variance during 1949-2012. Variation of the Hawaiian high's pressure is the major factor impacting winter precipitation in both Northern and Southern California. Smaller contributions are made by variations of the longitudinal position of the Hawaiian high to Northern California and by ENSO to Southern California. By comparison, the Pacific-North American (PNA) pattern does not significantly impact winter precipitation over California. The interannual fluctuations of the Hawaiian high's pressure in winter are related to diabatic heating over the tropical Pacific and the Aleutian region, and are not related to diabatic heating over the West Coast of the United States. The Hawaiian high's pressure and its latitude and longitude positions do not show decadal trends, and their interannual variations are not correlated with air temperatures averaged over the Northern Hemisphere.