The IRI has prepared this experimental Climate Outlook for Australia for February - July 2013. Of relevance in the preparation of this outlook is a good likelihood that the western tropical Pacific SSTs will be slightly above average while the east-central and eastern parts will be slightly below average during all four lead times. Such tropical Pacific conditions are indicated in the SST predictions on which these climate forecasts are based (SSTs). See the IRI's ENSO update for a discussion on the ENSO outlook (see IRI Probabilistic ENSO forecast). Slightly above average SST is predicted over much of the equatorial Indian Ocean during the first two forecast periods, weakening for the 3rd and 4th periods. During the first forecast period, SSTs in the northern tropical Atlantic are predicted to be very slightly above average to the north of the equator, and near average along and south of the equator. During the last three forecast periods SSTs in most of the tropical Atlantic are predicted to be near average. (February-April 2013, March-May 2013, April-June 2013, May-July 2013).

METHODS -

This Outlook was prepared using the following procedures and information:

A) Coupled ocean-atmosphere model predictions of tropical Pacific SST covering the forecast period. Particularly heavy weighting has been given to predictions from the coupled model operated by the NOAA National Centers for Environmental Prediction, Climate Modeling Branch. This model suggests a continuation of near-average conditions during the first forecast season. The forecast for near-neutral conditions is consistent with some, but not all, numerical and statistical forecasts of central and eastern Pacific SSTs.

B) Forecasts of the tropical Indian ocean using a statistical model developed by the IRI.

C) Global atmospheric general circulation model (GCM) predictions of the atmospheric response to the present and predicted sea-surface temperature patterns.

D) Other sources of information include NASA's Seasonal to Interannual Prediction Project (GSFC-NASA) and also seasonal prediction research at COLA.

The procedures, models, and data used to derive this Climate Outlook may be somewhat different from those used by the national meteorological services in the region. Thus, this product may differ from the official forecasts issued in those areas. The Climate Outlook for February - July 2013 is dependent on the accuracy of the SST predictions. For the tropical Pacific, these predictions can be expected to provide useful information, but there is some uncertainty concerning the evolution of SSTs. Spread in global SST predictions is a source of uncertainty in the Outlook provided here. Note that even if perfectly accurate SST forecasts were possible, there would still be uncertainty in the climate forecast due to chaotic internal variability of the atmosphere. These uncertainties are reflected in the probabilities given in the forecast.

It is stressed that the current status of seasonal-to-interannual climate forecasting allows prediction of spatial and temporal averages, and does not fully account for all factors that influence regional and national climate variability. This Outlook is relevant only to seasonal time scales and relatively large areas; local variations should be expected, and variations within the 3-month season should also be expected. For further information concerning this and other guidance products, users are strongly advised to contact their National Meteorological Services.

OUTLOOK -

This Outlook covers four seasons: February-April 2013, March-May 2013, April-June 2013 and May-July 2013. Maps are given showing tercile probabilities of precipitation and temperature. The maps for precipitation indicate the probabilities that the seasonal precipitation will fall into the wettest third of the years (top number), the middle third of the years (middle number), or the driest third of the years (bottom number). The color shading indicates the probability of the most dominant tercile -- that is, the tercile having the highest forecast probability. The color bar alongside the map defines these dominant tercile probability levels. The upper side of the color bar shows the colors used for increasingly strong probabilities when the dominant tercile is the above-normal tercile, while the lower side shows likewise for the below-normal tercile. The gray color indicates an enhanced probability for the near-normal tercile (nearly always limited to 40%). As before, numbers and their associated histograms show the probabilities of the three terciles. In areas with lots of spatial detail, there may not be sufficient room on the map, to allow histograms for each region. In those cases, some idea of the probabilities may be gained from the color alone. A qualitative outlook of climatology ("C") indicates that there is no basis for favoring any particular category. Areas that are marked by "D" represent regions for which less than 3cm of precipitation typically occurs over the season. Otherwise, for example, in the case of the islands of Vanuatu in February-April 2013 (Map A), there is a 40% probability that the precipitation will be in the wettest third of the years, a 35% chance it will be in the near-normal third of the years, and a 25% chance that the precipitation will be in the driest third of the years.

Maps of temperature show expected probabilities that the seasonal temperatures will fall into the warmest third of the years, the middle third of the years, or the coldest third of the years (Map A). The numbers for each region on the temperature maps indicate the probabilities of temperatures to fall in each of the three categories, above-, near-, and below-normal.

An additional precipitation map is provided for the first season indicating probabilities for extreme precipitation anomalies. Extremes are defined as anomalies that fall within the top and bottom 15th percentile of the observed records. A priori, there is a 15% probability of being within the extremely wet category, and a 15% probability of being within the extremely dry category, leaving a 70% probability that the precipitation will not be extreme. The maps indicate areas of increased risk of extreme precipitation totals. Three levels of increased risk are defined: slightly enhanced risk, enhanced risk, and greatly enhanced risk. For slightly enhanced risk, there is a 25-40% probability that precipitation will be within the indicated extreme, i.e. wet or dry. This represents an approximate doubling of the climatological risk. For enhanced risk, there is a 40-50% probability that precipitation will be within the indicated extreme. This represents an approximate tripling of the climatological risk. For greatly enhanced risk, the probability that precipitation will be within the indicated extreme exceeds 50%, i.e. the indicated extreme is the most likely outcome. A similar map is provided in the first season indicating probabilities of extreme temperature anomalies.

Boundaries between sub-regions should be considered as transition zones, and their location considered to be only qualitatively correct.

February-April 2013 through May-July 2013

The following tables summarize the precipitation and temperature probability forecasts:

               Summary of PRECIPITATION forecast for Australia


       Leads 1, 2, 3, and 4 refer, respectively, to the upcoming seasons:
             Feb-Mar-Apr   Mar-Apr-May   Apr-May-Jun   May-Jun-Jul


           A non-enhanced probability for above or below normal is 33%.
  (There is a near-normal category whose non-enhanced probability is also 33%.)


        The following countries or regions out of the  6 in Australia
      have at least half of their area under a PRECIPITATION forecast for:


                           At least            At least                      
     Substantially         slightly            slightly         Substantially
       enhanced            enhanced            enhanced           enhanced
      probability         probability         probability        probability
      (>48%) for          (>38%) for          (>38%) for         (>48%) for
     below normal        below normal        above normal       above normal



                        NEW ZEALAND
                           lead 4      




               Summary of  TEMPERATURE  forecast for Australia


       Leads 1, 2, 3, and 4 refer, respectively, to the upcoming seasons:
             Feb-Mar-Apr   Mar-Apr-May   Apr-May-Jun   May-Jun-Jul


           A non-enhanced probability for above or below normal is 33%.
  (There is a near-normal category whose non-enhanced probability is also 33%.)


        The following countries or regions out of the  6 in Australia
      have at least half of their area under a  TEMPERATURE  forecast for:


                           At least            At least                      
     Substantially         slightly            slightly         Substantially
       enhanced            enhanced            enhanced           enhanced
      probability         probability         probability        probability
      (>48%) for          (>38%) for          (>38%) for         (>48%) for
     below normal        below normal        above normal       above normal



                                            NEW ZEALAND
                                            leads 3 and 4  


                                            AUSTR-Western
                                               lead 4      


                                          AUSTR-NorthernTerr
                                           leads 1,2 and 3 


                                           AUSTR-Queensland
                                            leads 3 and 4  


                                             AUSTR-South
                                          leads 1,2,3 and 4


                                          AUSTR-NSW-Vic-Tasm
                                            leads 3 and 4  






OBSERVED CLIMATOLOGY DATA for Feb-Mar-Apr,
Mar-Apr-May, Apr-May-Jun and May-Jun-Jul 



CLIMATOLOGICAL AVERAGE: 

Temperature -
View Seasonal Temperature Climatology

Precipitation - 
View Seasonal Precipitation Climatology,


TERCILE THRESHOLDS (33%-ile & 67%-ile): 

Temperature -
FMA,
MAM,
AMJ,
MJJ

Precipitation - 
FMA,
MAM,
AMJ,
MJJ


EXTREME THRESHOLDS (15%-ile & 85 %-ile): 

Temperature -
FMA,
MAM,
AMJ,
MJJ

Precipitation - 
FMA,
MAM,
AMJ,
MJJ





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