Analysis of Tropical Cyclone Rapid Intensification in the Southwest Pacific Region

Abstract

This study statistically investigates the characteristics of tropical cyclones (TCs) undergoing rapid intensification (RI) in the Southwestern Pacific (SWP) region in the 37 years from 1986 to 2022. Among 364 TCs, 82 rapidly intensifying TCs (RI-TCs) were defined as TCs that experienced maximum wind speed increase of 30 kt (15.4 m s⁻¹) or more in a 24-h period. RI-TCs are frequently observed over the zonally elongated area around coral sea, south of Solomon Islands (Solomon Sea), Vanuatu, Fiji, Tuvalu, Tokelau and Samoa, while RI-TCs were rarely observed in areas of Tasman Sea, Tonga, northern waters of New Zealand, Cook Islands, Niue and French Polynesia. RI-TCs preferentially occur during the southern hemisphere summer season. Frequency of RI-TC occurrence shows a slowly increasing trend over the 37-year period. However, this increasing trend was not statistically significant at the 95 % confidence level. In El Niño years, TCs tend to undergo RI more frequently presumably due to the average genesis to the further north where sea surface temperature (SST) and ocean heat content were high. In contrast, RI-TCs occurred less frequently during La Niña years. The RI onset typically occurs 0–42 h after TC genesis with a peak frequency observed just after genesis (0–6 h). The RI duration is usually 1–2 days with a peak at 24 hours. The mean lifetime of RI-TCs lifetime was 7.86 days, longer than that of non-rapidly intensifying TCs (NR-TCs) (3.72 days). In terms of average intensity, RI-TCs have significantly lower lifetime central pressure and higher lifetime maximum wind speed than NR-TCs. RI-TCs tend to develop into more severe TCs as a result of formation in environments favorable for TC development such as weak vertical wind shear, deep moist layer, high SST and TC heat potential.