The impact of three recurving typhoons on eastern North Pacific predictability is examined using singular vector (SV) diagnostics. The leading SVs provide the fastest growing perturbations (in a tangent linear sense) to a given forecast trajectory. For this particular application, the SVs are constrained to provide the initial perturbations to which the 72-h forecasts over the eastern North Pacific are most sensitive. These SVs are calculated about the daily 00Z Navy Operational Global Atmospheric Prediction System (NOGAPS) operational forecasts for the months of October and November 2004.

During October-November 2004, there were three western Pacific typhoons, Ma-On, Tokage, and Nock-Ten that recurved to the north. Time-longitude plots of the SVs indicate a very large increase in the sensitivity of the eastern North Pacific to changes in the analysis in the western North Pacific each time one of these storms entered the mid-latitudes. SVs were calculated ignoring moist processes (dry), and including large-scale precipitation (moist). The increases in forecast sensitivity for the times when the storms enter the mid-latitudes were significantly larger for the moist SVs than for the dry SVs. Maps of the daily SV patterns indicate that the sensitivities associated with the three storms were quite different from one another. Detailed analysis of the SV sensitivity patterns associated with each storm will be presented. Implications for adaptive observing and ensemble design will be discussed.