The influence of eastern Pacific tropical cyclone remnants on the southwestern United States

Forty-three eastern North Pacific tropical cyclone remnants with varying impact on the southwestern United States during the period 1992-2005 are investigated.Of these, 35 remnants (81%) brought precipitation to some part of the southwestern United States and the remaining 8 remnants (19%) had precipitation that was almost entirely restricted to Mexico, although cloud cover did advect over the southwestern United States in some of these cases.Although the tropical cyclone-strength winds rapidly diminish upon making landfall, these systems still carry a large quantity of tropicalmoisture and, upon interaction withmountainous topography, are found to drop up to 30% of the local annual precipitation. Based on common rainfall patterns and large-scale circulation features, the tropical cyclones are grouped into five categories. These include a northern recurving pattern that is more likely to bring rainfall to the southwestern United States; a southern recurving pattern that brings rainfall across northern Mexico and the Gulf Coast region; a largely north and/or northwestward movement pattern that brings rainfall to the west coast of the United States; a group that is blocked from the southwest by a ridge, which limits rainfall to Mexico; and a small group of cases that are not clearly any of the previous four types. Composites of the first four groups are shown and forecasting strategies for each are described.