Assessment of the impact of increased lead time for tropical cyclone watches/warnings in the North Central Pacific

The lead times for watches and warnings for tropical storms and hurricanes were increased to 48 and 36 hours, respectively, for the Central North Pacific in 2009. This extra lead time was implemented to provide additional preparation time for emergency managers, media, and the public, especially in the main Hawaiian Islands, if tropical storm or hurricane conditions were forecast to impact any land areas in the area of responsibility (AOR) of the Central Pacific Hurricane Center (CPHC).

Hurricanes Felicia and Neki, which occurred in the Central North Pacific during 2009, required the issuance of watches with the longer lead times. Neki also required a hurricane warning before it impacted some islands which are part of the Papahanaumokuakea National Monument, northwest of the main Hawaiian Islands. In addition to actual watches and warnings, CPHC considered the potential impact these new lead times could have in other scenarios, by applying them to historical central Pacific tropical cyclones. These hypothetical exercises demonstrate the unique challenges with issuing tropical cyclone watches and warnings for relatively small and isolated geographic locations comprising most of the land areas in the CPHC AOR. Operational tropical cyclone wind speed probabilities, provided in tabular and graphical product formats with each full CPHC advisory package, were instrumental in the decision making process for the issuance, or simulated issuance, of these watches and warnings.

This presentation will summarize the impacts of the new tropical cyclone watch and warning lead times on CPHC operations during 2009. Also, we will examine how some historic Central North Pacific hurricanes, such as Iwa (1982), Iniki (1992), Emelia (1994), Ioke (2006), and Flossie (2007) might have been handled if they occurred with the longer lead times and the benefit of the wind speed probability products. This work is part of a broader effort in the National Weather Service to develop objective guidance for the issuance of tropical cyclone watches and warnings that are based on the tropical cyclone wind speed probabilities. It is also hoped that the result of these assessments will be useful to other tropical cyclone forecast centers around the world, especially in areas with small, isolated islands for which they have warning responsibility.