Tropical cyclone climatology, variability, and trends in the Tonga region, Southwest Pacific

The focus of several past tropical cyclone (TC) studies in the Southwest Pacific (SWP) had been primarily at the regional scale, with little or no attention to the local-scale TC activity (i.e., at the country level). With the growing coastal population in the South Pacific Island countries, as well as increasing threats from and exposure to climate extremes mostly affecting vulnerable communities, examining TC-related risks at the country level is more imperative now than before. This study catalogues for the first time the climatology, variability and trends of TCs affecting Nuku'alofa, the capital of Tonga using the Southwest Pacific Enhanced Archived for Tropical Cyclone (SPEArTC) dataset for the period between 1970 and 2019. The variability is examined in relation to the El Niño–Southern Oscillation (ENSO) phenomenon, which is the major driver of the year-to-year variability of TC activity in the SWP. A total of 128 TC tracks affected the Tonga region over the study period, with a seasonal average of ∼2.6 TCs per year. Of these, about 50% occurred during the peak months of January and February, and ∼38.8% of the total were of hurricane intensity (Categories 3, 4 and 5). Although differences were found between the average number of TCs per year during El Niño, La Niña and ENSO-neutral events (∼2.9, ∼2.6 and ∼2.3, respectively), they were statistically insignificant. No significant long-term trends were found in the number of TCs, severe TCs, and accumulated cyclone energy (ACE) over the period of study. The findings of this study will provide the information needed for disaster preparedness and TC predictions in Tonga.