The Reanalysis of the Tropical Cyclones Intensity in the South Pacific during the 1982-1983 El Nino

The South Pacific is the basin eastward of 135 degrees East. In this area, three agencies, the Bureau of Meteorology in Australia (BoM), the Joint Typhoon Warning Center (JTWC), and Meteo-France French Polynesia (MF), issued tropical cyclones warnings during the 1982-1983 summer. If the BoM was in charge of the western basin and MF of the eastern basin, the JTWC was the alone agency to deal with the whole South Pacific. Therefore, most of the data of the 1982-1983 tropical cyclones season came from the JTWC archives.

The data from the JTWC show that the South Pacific has had fourteen tropical cyclones having reached at least 35kt during the 1982-1983 summer. JTWC estimated that ten systems were at the hurricane intensity (at least 65kt) amongst which five intensified into category 3 cyclones with four formed east of the dateline. The BoM reported one Cat 4 cyclone, Elinor (February) at 115kt analysed at 75kt by JTWC west of 165 degrees East. Meanwhile, MF had observed one more cyclone than JTWC, Nano near 140 degrees West, in January, which has been estimated at 65kt over ten minutes.

Therefore, a summary of the archives from the three agencies gave fifteen tropical systems : four tropical storms, five cyclones (65kt to 95kt), and six major cyclones (100kt and more) including one cyclone at 115kt.

An important feature to consider is that this 1982-1983 cyclones season had never been reanalysed with the 1984 Dvorak's Technique which uses the enhanced infrared satellite pictures. Our research found that the cyclones intensity previously analysed has been strongly underestimated. If the overall number of storms and cyclones is quite the same, we highlighted that most of them was very intense : two and seven have been reanalysed at Cat 5 and Cat 4, respectively. Since the beginning of the satellite era, it is the only time that six Cat 4 and 5 cyclones have been observed east of the dateline. The 1983 El Nino produced in the whole south Pacific nine Cat 4 and 5 cyclones between January and April. The 1998 El Nino allowed the formation of eighteen tropical systems but only Susan and Ron reached the Cat 4 and 5. During the famous 2005 Hurricanes season of the North Atlantic, five cyclones had been estimated or measured at Cat 4 and 5 (NHC). Eight Cat 4 and 5 hurricanes formed for the 1997 El Nino in the eastern North Pacific (NHC). Only, the 1987, 1994, 1997 and 2004 western North Pacific seasons recorded more than the 1983 South Pacific season with eleven typhoons at Cat 4 and 5. Webster and al. (2005) had reported no Cat 4 and 5 cyclone in the South Pacific for the summer 1982-1983 while they found ten cyclones during the 1975-1989 period. As they gave twenty two cyclones for the 1990-2004, they concluded that the number of Cat 4 and 5 cyclones had doubled in this basin. The reanalysis of the 1982-1983 season brings a first response and confirmed that the archives of the south hemisphere needed to be revisited.