Pacific Climate Case Study: Tropical Cyclone Evan-A Rare Early Season Major Storm in the Southwest Pacific

Tropical Cyclone (TC) Evan was the first storm of the Southwest Pacific 2012/13 TC season. It was spawned on December 11, 2012, between American Samoa and Samoa and was tracked for a total of 16 days through December 26, 2012. According to the South Pacific Enhanced Archive of Tropical Cyclones (Diamond et al. 2012), from 1970-2012 there were a total of 22 Category 5 TCs in the Southwest Pacific on the Australian TC Intensity Scale , and during that period, Evan was only the 6th Category 5 TC to occur in the very early part of the season, from November to December.

Category 5 TCs are the most severe with maximum sustained winds exceeding 106 knots, and climatologically are most likely to occur in the latter portion of the TC season from February to April. In fact with respect to major TCs (category 3-5) in intensity, until Evan, since the 1969/70 season, there had only been 27 TCs to reach major TC status that early in the season; this equates to just over 30% of all TCs for the very early portion of the season from November to December.

This Pacific Climate case study will explore the unique early season nature of such an intense TC in the region, as well as looking for ways for forecasters to better track such a rapidly intensifying storm. The goal is to examine how forecasters at global, regional and local weather services create and convey the warnings and information associated with such a unique TC. Reducing loss of life and harm when a TC threatens depends on people receiving adequate and advance risk information that they can interpret and use in protective decision making. This brings up a number of key questions: (1) Were the weather services able to pinpoint Evan's forecast track and its intensity as it headed toward Samoa?; (2) Did the weather services issue the warnings on time?; (3) Were the warnings effective?; (4) How were the warnings communicated to the public?; (4) Are forecasters' current knowledge of forecasting TCs better now than say 20 years ago?; and finally, (5) What lessons can be learned from Evan? These questions cannot be fully addressed in this presentation, but will require an interdisciplinary team made up of TC warning system partners (e.g., forecasters, disaster managers and representatives from other user communities, social scientists), that need to convene in order to undertake a thorough assessment before the information and knowledge about Evan are lost.