Tropical Cyclone Outlook Summary For The Pacific Islands

• The NIWA and MetService assessment of tropical cyclone1 (TC) activity for the coming season indicates normal to below normal activity.
• Six to 10 named TCs could occur in the Southwest Pacific from November 2024-April 2025. The long-term average number of named TCs per season is around nine.
• TCs have a significant impact across the Southwest Pacific, with the season starting in November and lasting through April. For the coming season, significant differences are expected between the western and eastern halves of the basin.
• The risk of impact from a TC is expected to be higher near the Coral Sea, Solomon Islands, and Papua New Guinea, as illustrated in Figure 1. Normal to reduced risk is anticipated in the central and eastern part of the basin.

• Vanuatu and New Caledonia typically experience the greatest TC activity with an average of two or three TCs passing nearby each year.
• Normal or elevated activity: Papua New Guinea, Solomon Islands, and Northern New Zealand.
• Near normal activity: Vanuatu and New Caledonia.
• Normal or reduced activity: Tuvalu, Tokelau, Niue, Wallis & Futuna, Samoa, American Samoa, Society Islands, Fiji, and Tonga.
• Reduced activity: Southern Cook Islands and Austral Islands.
• Activity unlikely: Marquesas, Kiribati, Northern Cook Islands, Tuamotu Archipelago, and Pitcairn Islands.
• Between 3-4 severe TCs reaching category 3 or higher may occur anywhere across the region, so all communities should remain prepared.

• Past seasons with similar conditions to the present, called “analogue years”, suggest multiple TCs could intensify to at least category 3 strength.

• Category 5 strength TCs2, in which sustained winds are 200 km/h or greater, are associated with a majority of the analogue years.

• Despite the official season running from November through April, TCs sometimes occur out-of-season.

• It does not take a direct hit or severe TC to cause considerable damage or life threatening weather. When dangerous weather is forecast, please heed the advice of your local meteorological service, civil defence, or disaster management office.

Tropical cyclone outlook summary for New Zealand

• On average, at least one ex-TC passes within 550 km of New Zealand each year. This season, the risk is considered normal-elevated.

• If an ex-TC tracks close to the country, there is a near-equal probability of it tracking to the east or west of the North Island based on historical climate data.

• Two out of five analogue years considered in this outlook had at least one ex-TC passing within 550 km of the country.

• Analogue years suggest that a decaying ex-TC entering the New Zealand region could affect maritime and coastal areas around the North Island, but an interaction with the South Island cannot be ruled out.

• Significant rainfall, extreme winds, hazardous marine conditions, and coastal damage are all possible leading up to and during ex-TC events.

• The effects of ex-TCs can also be spread over a large area, particularly if the decaying ex-TC interacts with mid-to-high latitude weather systems.

El Niño-Southern Oscillation outlook

• The El Niño Southern Oscillation (ENSO), comprised of La Niña, neutral, and El Niño phases, plays an important role in year-to-year regional TC development and spatial coverage and is a key factor in this outlook.

• As of early October 2024, sea surface temperatures across the eastern and central equatorial Pacific Ocean are below average and close to La Niña thresholds. 

• Atmospheric circulation patterns related to ENSO over French Polynesia and northern Australia indicate neutral ENSO conditions as of early October 2024. 

• Oceanic and atmospheric forecasts for ENSO suggest La Niña, of weak-to-moderate intensity, has a 60-70% chance of emerging by December 2024. La Niña conditions, should they develop, are likely to persist through the back half of the TC season in February-April.

• The progress of ENSO and TC activity will continue to be tracked with an update to this guidance in January 2025 if needed.

[1] Tropical cyclones are categorised in strength from 1 to 5, with 5 being most intense. Tropical cyclones that reach category 3 or higher are classified as severe, with mean (10 minute) wind speeds of at least 119 km/h.

[2] Since quality observations began in the early 1970s, there has been a trend toward fewer but stronger TCs.

© Scoop Media