Exceptional Ella - a 20-year event [1]
Wednesday, May 10, 2017 - 18:01. Updated on Wednesday, May 10, 2017 - 22:55.
It is unusual to see so many cyclones in the South Pacific at this time of the year, says Tonga's Director of Meteorology, 'Ofa Fa'anunu today, as northern Tonga remains on a Warning for Tropical Cyclone Ella [upgraded to Category 2 this evening 10 May 2017].
Tonga's cyclone season usually runs from November to April.
"Although uncommon, cyclones do form outside the cyclone season. The last one was Severe Tropical Cyclone Keli in June 1997," said 'Ofa.
"Cyclones need to have enough moisture (water vapour) to form. Right now the waters between Vanuatu and Tonga are 1.5 to 2 degrees above normal. So there is fuel there for cyclone formation. Usually by this time, the ocean is too cold for cyclone formation," he said.
"This could be an indication that another El Nino might be forming but will know for sure in another two months or so."
This may be a climate change indicator.
"We need a longer data set to confirm if this is the cause of climate change. But yes, since 1950’s the temperature of the earth has steadily increased. What we can confirm is we are seeing an increasing trend in Category 4 and Category 5 tropical cyclones in the South West Pacific. But yes, the climate change projections include the likelihood of an extended Tropical Cyclone season in a warmer climate," he said.
Last week slow moving Tropical Cyclone Donna, categorised as a Category 5 by Fiji Meteorological Service, caused gales and heavy rain in northern Vanuatu. It has weakened moving southeast this week but is still slow moving in the tropics. The remains of the system might pass close to the northern and eastern parts of New Zealand toward the end of the week.
This week Tropical Cyclone Ella is moving through northern Tonga toward Fiji where it is forecast to increase strength to a Category 2 storm.