Southern Hemisphere Application of the Systematic Approach to Tropical Cyclone Track Forecasting. Part III : updated environmental structure characteristics

Abstract

The Meteorological knowledge base of the Systematic Approach to tropical cyclone track forecasting in the Southern Hemisphere has been updated to reflect a more global terminology. Examples of these new environment structures in operational (NOGAPS) analyses and tracks are given. Perhaps the most important conclusion is that all cases in the 1990-91 through 1998-1999 seasons could be classified into one of these 14 synoptic pattern/region combinations. The nine-year "climatology" of the occurrences of each ofthe 14 combinations is given for the South Indian and Pacific Oceans separately, and the characteristic tracks in each of these 14 combinations are provided. Some new transitional mechanisms between these combinations have also been defined. The importance of these transitions from one pattern/region combinations to another is that the TC track then also changes. The frequency of recurring (greater than three) transitions in this nine-year sample is summarized. Because the TC is at any time in only one pattern/region combination, the concern of the forecaster is on the possible transitions from that pattern/region. To assist the forecaster, the percentages of these transitions from each pattern/region combination are also summarized. Some ofthese transitions are clearly more favored than others, which is useful guidance to the forecaster.