#AU #Outlook #Corp National temperature & rainfall for September to November 2013 National temperature outlook for September to November: Warmer spring days more likely for most of the tropics and Tasmania. The chances of the spring maximum temperature exceeding the long-term median maximum temperature are greater than 60% over the tropical north, the western WA coastline, and Tasmania (see map above). Such odds mean that for every ten years with similar climate patterns to those currently observed, about six to eight spring periods would be expected to be warmer than average over these areas, while about two to four years would be cooler. Conversely, there is a 30 to 40% chance of warmer than normal days over southern NSW, northern and central Victoria and far southeastern parts of SA. In other words, there is a 60 to 70% chance of cooler than normal days over these areas. The chance that the average minimum temperature for spring will exceed the long-term median minimum temperature is in excess of 60% over the northern half of the continent, extending through western WA, central SA and Tasmania. Probabilities exceed 80% over the tropical northern coasts, the far southwest and Tasmania. Over the rest of the country, the chances of warmer or cooler night-time temperatures are roughly equal. Climate influences The negative Indian Ocean Dipole (IOD) event that has been influencing Australian climate since mid-May has weakened over the past four weeks. Despite this, sea surface temperature patterns continue to be consistent with a negative dipole event. The majority of climate models expect this negative IOD event to persist until mid-spring. A negative IOD during the winter-spring period increases the chances of above normal rainfall, and thus cloud amount, over southern Australia. Increased cloudiness reduces sunshine hours, and hence daytime temperatures, over inland Australia, while over parts of northern Australia it increases the chance of higher humidity. The tropical Pacific has remained ENSO-neutral since mid-2012. The dynamical seasonal outlook model suggests ENSO-neutral conditions will remain for the rest of 2013. This means there is no strong shift in the odds from the tropical Pacific, and is reflected to some degree in the temperature outlook, with much of the southern half of the country having odds close to 50% for maximum temperatures. Warmer than normal sea surface temperatures currently surround much of Australia. Warmer sea surface temperatures will tend to influence air temperatures in those areas closer to the coast Summary Warmer spring days are more likely over most of northern Australia, coastal WA, and Tasmania, while cooler days are more likely across central and northwest Victoria. Warmer nights more likely over the northern half of the continent, coastal WA and Tasmania. Climate influences include a weakening negative Indian Ocean Dipole, a neutral-to-cool tropical Pacific, and locally warm sea surface temperatures Outlook accuracy for maximum temperatures is moderate to high over Australia excluding parts of WA, with minimum temperature accuracy moderate to high over most of southern and eastern parts of Australia. National rainfall outlook for September to November: The chance of exceeding the median rainfall for spring is more than 60% over most of southeast Australia and the Top End of the NT. The chance rises to more than 70% over central Victoria. Such odds mean that for every ten years with similar climate patterns to those currently observed, about six to seven spring periods would be expected to be wetter than average over these areas, while about two to three would be drier. Odds suggest a less than 40% chance of above average rainfall over southern parts of the Kimberley in WA. In other words, the chance of below normal rainfall is greater than 60%. The chance of receiving a wetter or drier than normal spring is roughly equal (i.e., close to 50%) over the remainder of the country. Climate influences: The negative Indian Ocean Dipole (IOD) event that has been influencing Australian climate since mid-May has weakened over the past four weeks. Despite this, sea surface temperature patterns continue to be consistent with a negative dipole event. The majority of climate models expect this negative IOD event to persist until mid-spring. A negative IOD during winter-spring increases the chances of above-average rainfall over southern Australia, while over parts of northern Australia it increases the chance of higher humidity. This is reflected in the rainfall outlook, with most of southeast Australia expecting above normal rainfall. The tropical Pacific has remained ENSO-neutral since mid-2012. The dynamical seasonal outlook model suggests ENSO-neutral conditions will remain for the rest of 2013. This means there is no strong shift in the odds from the tropical Pacific, and is reflected to some degree in the rainfall outlook, with much of the country having odds close to 50%. Warmer than normal sea surface temperatures currently surround much of western and southern Australia. Warmer sea surface temperatures can provide more moisture to the atmosphere, which in combination with the right weather systems (e.g. interactions with fronts or northwest cloudbands) may result in increased rainfall. Bureau climatologists continually monitor the climate for any significant developments, with information on the likelihood of El Niño/La Niña and IOD events available fortnightly at the ENSO Wrap-Up. For a summary of Pacific and Indian Ocean outlooks, please see the Climate Model Summary. Summary: A wetter than normal season is more likely for southeast Australia and the Top End of the NT The chances of a wetter or drier than normal season are roughly equal over Queensland, most of South Australia, most of Western Australia and the rest of the NT Climate influences include a weakening negative Indian Ocean Dipole, a neutral-to-cool tropical Pacific, and locally warm sea surface temperatures Outlook accuracy is moderate over most of Australia, except for parts of western WA and western and northern parts of SA
Posted on: Wed, 28 Aug 2013 02:05:05 +0000
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