METEOROLOGICAL SERVICES DEPARTMENT

MINISTRY OF TRANSPORT AND COMMUNICATIONS

Prediction of the OND 2004 and JFM 2005 Rainfall for Zimbabwe

(OND Refers to the period October to December, and JFM denotes the period from January to March)

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Abstract:

This report gives a technical summary of the seasonal rainfall forecast for the 2004-05 early summer and late summer. Each period is made up of three months. The early summer, normally referred to as the first half of the season, covers the period October–to-December, inclusive, while late summer (also referred to as second half) spans from January to March. The forecasts presented here are based on a combination of statistical methods, numerical weather prediction models and expert judgement. With respect to statistical analyses, the results relate the three-month area-averaged rainfall over homogeneous rainfall zones in Zimbabwe to changes in sea surface temperatures. These sea surface temperatures have been found to have a bearing on the total rainfall amounts that fall over the country. This relationship, though, is not one-to- one. In other words, there are some instances when the two are totally unrelated. Three homogeneous zones were identified for each half. The zones are however specific to each half.

Results of the analyses show that there are higher chances for near-normal to above–normal rainfall occurring over Zimbabwe in the first half of the season (October to December 2004) but higher chances for below-normal to normal rainfall for the remainder of the season (i.e. January to March 2005).

Please note

The rainfall forecast comes against a backdrop of a weak El Nino that is developing in the equatorial pacific. The Department is monitoring this event and will issue regular updates. Another detailed and revised forecast for the period January-March 2004 will be issued in mid-December. In the meantime, the Department will start issuing its 10-day weather forecasts for the 2004-2005 season from mid- October.

Forecasts

The maps below summarize the rainfall forecast for each half of the season. The probabilities refer to the area-averaged rainfall and local variations are expected.  The forecasts are expressed in probabilistic terms, which give the probability of rainfall in a given zone being in any one of the three categories, namely the above normal, near normal and below normal categories.  The objective is to give the decision makers all probable scenarios so as to take care of all possible outcomes. For example, even if the forecast is for above normal rainfall, there are also chances, though low, of drought occurring.