Eight tropical cyclones crossed the Exclusive Economic Zones of the South Pacific this 2019 – 2020 tropical cyclone season that officially ended in April. In Meteorological terms, this is known as a ‘near normal’ season.
Tropical Cyclones Rita, Sarai, Tino, Uesi, Vicky, Wasi, Gretel and Harold wreaked havoc across the Pacific islands highlighting the need for ongoing work to build Pacific resilience.
“The impacts of climate and weather on our Pacific people are real. Our livelihoods and our lives depend on how we can best prepare for those impacts. The work of our Pacific Met Services and partners through the Pacific Met Desk Partnership plays a crucial role in helping people prepare,” said Ms Tagaloa Cooper, Director of Climate Change Resilience programme of the Secretariat of the Pacific Regional Environment Programme (SPREP).
“Working collectively together, we can strengthen the services we provide to our Pacific island people – we are very grateful for the PacMetDesk Partnership mechanism. Our thoughts are with all our Pacific communities who have been heavily impacted by any of the cyclones that have crossed their paths this season.”
To help Pacific islands prepare for the cyclone season, a 5th Pacific Climate Outlook Forum (PICOF) was held in Noumea, New Caledonia in October last year to develop a statement forecasting what is to be expected.
The forecast statement was a team effort from the providers and the climate officers from the National Meteorological Services. After discussing and comparing the available tropical cyclone forecasts for several days at PICOF-5, forecasters came to the consensus that a near normal tropical cyclone activity was most likely in the Southwest Pacific for the 2019-20 season. The long-term average is nine cyclones east of the tip of Cape York, Australia.
The forecast was for the persistence of El Niño-Southern Oscillation (ENSO) neutral conditions, rather than El Niño or La Niña, which leads to lower predictive ability. Despite this challenge, forecasters identified an area of warmer than average ocean water in the west-central tropical Pacific as a possible driver of rainfall and cyclone activity. Another component of the forecast was for below normal rainfall, and associated cyclone activity, in the western Coral Sea, consistent with below average sea temperatures in the region.
The forecast of a near normal season was spot-on: there turned out to be eight tropical cyclones east of the tip of Cape York, Australia with severe cyclones being Rita, Tino, Uesi, and Harold. Harold was one of the most intense cyclones to make landfall in the Pacific Islands during April on record.
The cyclone activity was strongly influenced by a warm area of ocean water in the west-central Pacific, as expected — a rising branch of the Walker Circulation focused over this region, acting as a focal point for cloud cover, rainfall, thunderstorms and tropical cyclone genesis.
Additionally, rainfall and cyclone activity was below normal in the Coral Sea as expected with only one cyclone forming in this region.
According to Mr Ben Noll, a meteorologist of the National Institute of Water and Atmospheric Research of New Zealand, “At PICOF, the team arrived on a forecast of near normal tropical cyclone activity through consensus. Our statement spoke to the chance for reduced rainfall in the Coral Sea region, which also ended up happening. We didn’t expect a hyperactive season and get a very quiet one or vice versa. All up, it was a pretty decent forecast effort from the group.”
Although skill may have been limited by ENSO-neutral conditions, forecasters used their experience to identify areas of heightened tropical cyclone risk. This also proved the power of teamwork and partnership as the forecast put the Pacific islands in the best possible position to prepare and plan for the 2019-2020 season.