Wednesday, 13 January 2010

What El Niño might bring

It might be abnormally cold on land in much of the northern hemisphere at the moment but it’s a warm old time in the world’s oceans. During the last four weeks, equatorial sea surface temperatures have been above-average across the Pacific and Indian Oceans and over large areas of the Northern Hemisphere subtropics including in the Atlantic.
The US National Oceanic and Atmospheric Administration provides the picture.
The NOAA’s National Weather Service sees the above average Pacific water temperatures as consistent with El Niño which is expected to exert a significant influence on the global weather and climate in the coming months. For the contiguous United States, potential El Niño impacts include above-average precipitation for the southern tier of the country, with below-average precipitation in the Pacific Northwest and in the Ohio and Tennessee Valleys. Below-average snowfall and above-average temperatures are most likely across the northern tier of states (excluding New England), while below-average temperatures are favored for the south-central and southeastern states.
As for Australia the Bureau of Meteorology sees better than 50% chance that some relief from hot weather is on the way for south eastern Australia. The national outlook for the March quarter (January-March) mean maximum temperatures, shows moderate to strong shifts in the odds favouring above average values in the west of WA and in a broad region covering much of northern and northeast Australia. In contrast, cooler than average daytime temperatures are indicated in the southeast of the country.
The chance that the average January-March maximum temperature will exceed the long-term median maximum temperature, is between 60 and 65% in western WA and between 60 and 90% northeast of a line from Derby in northern WA to Sydney (see map).
This means that for every ten years with ocean patterns like the current, about six to nine March quarters would be expected to be warmer than average over these areas, while about one to four would be cooler. In contrast, there is a 60 to 70% chance of cooler than normal days averaged across the season over Tasmania, Victoria and southern SA.
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