Climate Outlook - Rainfall & Temperature

AUSTRALIA AND INDONESIA April - September 1998

The IRI Experimental Forecast Division has prepared this Climate Forecast Outlook for Australia for April - September 1998. Of relevance in the preparation of this Outlook has been the strong El Niņo episode now subsiding in the tropical Pacific, and the expectation that warm El Niņo conditions will persist at least for the next few months. Also relevant to this outlook are warm sea surface temperature (SST) anomalies in the Indian ocean.

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 that warm anomalies will persist in the tropical Pacific through the forecast period.

B) Statistical predictions of the tropical Indian SST's.

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

D) Statistical analyses of the observed climate system over Australia and Indonesia.

E) Additional information available from the Department of Natural Resources , Queensland, Australia.

The procedures, models, and data used to derive this Climate Outlook may be somewhat different from those used by the national meteorological services in Australia. Thus, this product may differ from the official forecasts issued in those areas. This Outlook has been prepared in the time available, using all information that was reasonably accessible. Inclusion of other climate information and guidance requires further arrangements. The IRI is engaged in establishing such collaborative arrangements with the goal of improving its capability to provide the best and most complete global climate guidance. The Climate Outlook for April-September is dependent of the quality of the SST predictions. For the tropical Pacific, these predictions can be expected to provide useful information, but there is considerable spread in coupled model predictions concerning the evolution of SSTs. This spread in predictions is a primary source of uncertainty in the Outlook provided here, which assumes that tropical Pacific SSTs will continue to decline at a modest rate. Also, it is known that Indian ocean SST anomalies may play some role in modulating rainfall and temperature changes over Australia and Indonesia. Thus, the uncertainties in the Indian ocean SST values during the forecast period may lead to additional uncertainty over some parts of Australia and Indonesia.

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. For further information concerning this and other guidance products, users are strongly advised to contact their National Meteorological Services.

OUTLOOK -

This Outlook covers two seasons: April-June and July-September 1998. Maps are given showing expected probabilities of precipitation. The maps 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). An additional 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. 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. A qualitative outlook of climatology ("C") indicates that there is no basis for favoring any particular category. Otherwise, for example, in the case of the east coast in April-June 1998 (Map A), there is a 25% probability that the precipitation will be in the wettest third of the years, a 40% chance it will be in the near-normal third of the years, and a 35% chance that the precipitation will be in the driest third of the years. The numbers for each region on temperature maps indicate the probabilities of temperatures to fall in each of the three categories, above-, near-, and below- normal. Boundaries between sub-regions should be considered as transition zones, and their location considered to be only qualitatively correct. Boundaries between sub-regions should be considered as transition zones, and their location considered to be only qualitatively correct.

April-June 1998

PRECIPITATION

The map is dominated by the following main regions of enhanced probabilities of precipitation anomalies:

P.A) The region of elevated probabilities for normal to below-normal precipitation over the east coast of Australia.

P.B) The area indicating slight enhancement of probabilities for normal precipitation over the northern regions of Australia

P.C) Enhancement of probabilities for below-normal precipitation over the northern part of the west coast.

P.D) The region of elevated probabilities for normal to below-normal precipitation over the southern part of the west coast of Australia.

P.E) Enhanced probabilities for above-normal precipitation over the South Island of New Zealand.

P.F) Enhanced probabilities for below-normal precipitation over the North Island of New Zealand.




TEMPERATURE

The main features of the pattern of probabilities for temperature field are:

T.A) Highly enhanced probabilities for above-normal temperatures over Australia.

T.B) Enhanced probabilities for above-normal temperatures over the maritime sub-continent.

July - September 1998

PRECIPITATION

The main features of this season are as follows:

P.i) Enhanced probabilities for above-normal participation over the western half of Indonesia.

P.ii) Enhanced probabilities for above-normal participation over the east coast of Australia.

P.iii) Enhanced probabilities for above-normal precipitation over the South Island of New Zealand.

P.iv) Enhanced probabilities for below-normal precipitation over the North Island of New Zealand.

TEMPERATURE

The main features of the pattern of probabilities for temperature field are:

T.i) Enhanced probabilities for warm temperatures over Indonesia.

T.ii) Enhanced probabilities for warm temperatures over the east coast of Australia.

T.iii) Enhanced probabilities for near-normal temperatures over the New Zealand.

Cutoffs and Max/Min extremes for AMJ and JAS.

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