Tropical cyclone outlook update: normal

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Climate and weather organisations across the Pacific are still predicting near normal tropical cyclone activity across the southwest Pacific for the rest of the season through to April. On average, nine tropical cyclones occur in the region each cyclone season (Nov-Apr).

New Zealand’s National Institute of Water & Atmospheric Research (NIWA) has issued the tropical cyclone outlook on behalf of collaborating organisations from New Zealand, the US, Fiji, Australia, French Polynesia, and the Cook Islands.

The updated outlook for the second half of the season says that near normal tropical cyclone activity is likely for most countries in the southwest Pacific during the remainder of the cyclone season from February to April. Countries east of the date line, including Niue, Tonga, and the Southern Cook Islands are at higher risk than normal because of El Niño conditions. Parts of southwest French Polynesia (Society and Austral Islands) can be affected by tropical cyclones during El Niño, so these islands should also remain vigilant.

Outlook in more detail:

El Niño conditions currently exist in the region. Equatorial sea surface temperature anomalies are positive and the atmosphere has shown a classic low pressure anomaly over southern French Polynesia, with higher pressures over eastern Australia for most of summer.  The expectation is that near normal tropical cyclone (TC) activity will occur for most countries in the southwest Pacific during the remainder of the season February – April. Communities should remain alert and prepared.

As previously forecast for this season, TC activity is expected to be near normal with 8–11 TCs expected over the November 2009 – April 2010 period for the southwest Pacific. On average, nine tropical cyclones occur each year for the southwest Pacific region. Southwest Pacific TCs are grouped into classes ranging from 1 to 5, with 5 being the most dangerous. For the present season, two or three storms were forecast to reach at least Category 3, and one storm was expected to reach at least Category 4, with mean wind speeds of at least 64 knots or 118 km/h.

Updated projections show an increased risk of tropical cyclones for the 2009–10 season exist to the east of the date line, particularly for the Southern Cook Islands. Increased risk east of the date line also exists for Niue and Tonga. To the west, there is also increased risk for the Solomon Islands. It should be noted that TCs can affect parts of southwest French Polynesia (Society and Austral Islands) during El Niño. These islands should remain vigilant as El Niño continues to evolve with progression into austral autumn. Though a moderate El Niño exists, the number of TCs entering a 550km radius of the New Zealand coast is expected to remain about normal. On average every other year one TC affects New Zealand during the last half of the season.

 
Contacts for more information

Dr Andrew Lorrey
NIWA
Tel: +64 9 375 2055

Dr James Renwick
NIWA
Tel: +64 4 386 0343
Mob: +64 21 178 5550

In the Pacific Islands, please contact your local Meteorological Service.

This tropical cyclone information has been prepared as a regional collaboration, with contributions and consensus about this outlook from NIWA, New Zealand MetService Ltd, NOAA, Fiji Meteorology Service, Australian Bureau of Meteorology, Meteo-France, and the Cook Islands Met Service. 

Tropical Cyclone Frequency

Table 1: The average number of tropical cyclones passing within 5° of the main South Pacific Island groups between February and June.


Departure from normal of the number of Tropical Cyclones occurring later in the season (February-June) in the southwest Pacific, in years with similar SST anomalies and SOI to the present situation, and a weakly coupled El Nino in the prior Austral autumn/spring. The analogue years chosen for the guidance are listed at the top of the table above, and were selected from the 1957-58 to 2008-09 period. Only three analogue seasons were found within the 1969-70 to 2008-09.