Contribution of tropical cyclones to the North Pacific climatological rainfall as observed from satellites

Tropical cyclone monthly rainfall amounts are estimated from passive microw ave satellite observations for an 11-yr period. These satellite-derived rai nfall amounts are used to assess the impact of tropical cyclone rainfall in altering the geographical, seasonal, and interannual distribution of the N orth Pacific Ocean total rainfall during June-November when tropical cyclon es are most important. To estimate these tropical cyclone rainfall amounts, mean monthly rain rate s are derived from passive microwave satellite observations within 144-km r adius of the center of those North Pacific tropical cyclones that reached s torm stage and greater. These rain-rate observations are converted to month ly rainfall amounts and then compared with those for nontropical cyclone sy stems. The main results of this study indicate that 1) tropical cyclones contribut e 7% of the rainfall to the entire domain of the North Pacific during the t ropical cyclone season and 12%, 3%, and 4% when the study area is limited t o, respectively, the western, central, and eastern third of the ocean; 2) t he maximum tropical cyclone rainfall is poleward (5 degrees -10 degrees lat itude depending on longitude) of the maximum nontropical cyclone rainfall; 3) tropical cyclones contribute a maximum of 30% northeast of the Philippin e Islands and 40% off the lower Baja California coast: 4) in the western No rth Pacific, the tropical cyclone rainfall lags the total rainfall by appro ximately two months and shows seasonal latitudinal variation following the Intertropical Convergence Zone; and 5) in general, tropical cyclone rainfal l is enhanced during the El Nino years by warm SSTs in the eastern North Pa cific and by the monsoon trough in the western and central North Pacific.