SUBJECT :Wheather 

It's a great time to be a weather watcher if extremes or unusual events get your pulse running.

Australia entered July with little if any natural snow on its alpine peaks although Thursday's cold front helped bring some relief to the struggling ski resorts. Further fronts may bring much-needed reinforcements of snow early next week.

What transfixed meteorologists in the Pacific, though, was the formation of Cyclone Raquel north of the Solomon Islands.

For the southern hemisphere, tropical cyclones have not been recorded in winter since the arrival of the satellite era brought reliable storm detection.

And to the north, tropical storm Chan-Hom will likely spin to typhoon strength and bear down on Guam over the weekend. A series of other tropical lows is also lining up across the western Pacific.

Satellite image show Chan-Hom at the upper left and Raquel below. Photo: NASA

Populations in the storms' path will face immediate threats but the impacts of this week may be felt far wider if, as expected, Raquel and its siblings across the equator give momentum to the strengthening El Nino that has taken hold in the central and eastern Pacific.

"It's a beautiful situation – if not for the Solomon Islands – but just meteorologically, it's amazing," Axel Timmermann, a professor of oceanography and El Nino specialist at the University of Hawaii, said.

Raquel, Chan-Hom and the other storms are "going to intensify the current conditions, and generate more momentum for the El Nino maturation" for the late southern winter and into the spring, Timmermann said.

El Ninos – and their opposite, La Ninas – are the biggest drivers of the global climate. An El Nino is characterised by the central and eastern equatorial Pacific warming faster than areas in the west as the normally easterly blowing trade winds stall or are reversed.

The storms will foster that development by sending westward wind bursts along the equator.

Rainfall patterns and temperatures shift during these fluctuations, with El Ninos typically marked by heatwaves and reduced rainfall in western parts of the Pacific including Australia, while eastern Africa and nations fringing the eastern Pacific tend to get unusually heavy rains. La Ninas produce the opposite effects.

Some – but not all – of Australia's worst snow seasons have been in El Niño years, as have big bushfires such as the Ash Wednesday blazes during the intense 1982-83 event.

And, as the Bureau of Meteorology is noted in its drought updateon Friday, the regions recording severe rainfall deficits compared with average years now include areas where rains are usually among the most reliable such as south-west Victoria.

Michael McPhaden, a senior scientist with the US National Oceanic and Atmospheric Administration, says Cyclone Raquel and the other storms could spur a particularly big El Nino.

"All the elements are in place for a major El Nino this year and the latest westerly wind burst will hit the accelerator on further warming," McPhaden says.

"Based on what we've seen so far in 2015, this event could shape up to be as big as the 1997-98 and 1982-83 El Ninos, which were the strongest on record."

However, Harry Hendon, a senior principal research scientist at the Bureau of Meteorology, cautions that forecasting the magnitude of an El Nino is difficult at this time of year. The particular tropical pulse that helped set up Cyclone Raquel – known as a Madden-Julian Oscillation - could also be followed by a counter phase that would quell some of the eastward-wind bursts.

"The current forecasts indicate the most likely outcome is the occurrence of a moderately strong El Nino that peaks in late spring, but the range of possible amplitude is relatively large," Hendon says.

Wenju Cai, a CSIRO research director, likens this week's storms to 1972 when Cyclone Ida emerged in late May and into June, the last time the Queensland region had a tropical storm so far out of season.

Cai says the background global warming makes it more likely to have cyclones form "to kick start the season", since such events need a minimum sea-surface temperature of 26.5 degrees.

"Often in June or July, westerly winds are hard to generate because the trade winds are quite strong in those months," Cai says.

Cai agrees that it is too early to tell how strong this year's El Nino will be but notes that the 1972 event was exceeded by intensity in the 20th century only by the 1982-83 and 1997-98 ones.

Whatever its eventual strength, though, this year's El Nino may have another impact – putting to rest any remaining doubts about a "hiatus" in global warming, Timmermann says.

El Ninos tend to lift global surface temperatures by 0.1-0.2 degrees, and the first five months of 2015 are running 0.09 degrees above the previous record set in 2010 when the most recent El Nino was maturing, NOAA said last month.

"For this year, 2015, we're going to have record-breaking global mean surface temperatures unless there's a volcanic eruption happening soon," Timmermann predicts.


Source: 3 July, 2015, The Sydney Morning Herald