Precipitation Outlook for the Caribbean
Background
The Precipitation Outlook for the Caribbean is prepared by the Caribbean Institute for Meteorology and Hydrology with contributions from some regional Meteorological Services.

The outlook is produced by combining objective input (dynamic climate model output) and subjective input (experience). Precipitation forecasts from several global climate models, in the form of anomalous precipitation as a percentage of average seasonal rainfall or of probabilities of above-, near-, or below normal rainfall, are used. Currently output from climate models from the International Research Institute for Climate Prediction (IRI), the United Kingdom meteorological Office (UKMO), and the European Centre for Medium-Range Weather Forecasts (ECMWF) are examined.

Precipitation probabilities are estimated for a number of sub-regions based on the model forecasts, the level of agreement between the different models, and a subjective confidence in the different predictions based on current conditions and a knowledge of the local climatic conditions. In addition, the probabilities provided by the various contributors are consulted to present a consistent forecast.

The precipitation outlook is issued in the form of a map of tercile probabilities showing regions having homogeneous forecast probabilities for below, near, and above normal precipitation. The terciles separate the possible outcomes into three categories (terciles) based on the historical precipitation record. The probabilities add up to 100.

Tercile probabilities separate the possible outcomes into three categories – terciles (thirds) - based on the historical precipitation record. The three categories are:

The tercile probabilities are presented in the form:

20

45

35

Percentage likelihood of above normal rainfall

Percentage likelihood of normal rainfall

Percentage likelihood of below normal rainfall

In this example, there is a 20% probability (chance) that the rainfall for the period will be in the upper tercile (wet), a 45% probability of being in the middle tercile (normal), and a 35% probability that the rainfall will be in the lower tercile (dry). Overall, this may be interpreted that the rainfall for this period is more likely to be normal to dry.

A few words of caution. This outlook is relevant only to seasonal time scales and relatively large areas; local variations should be expected, and variations within the 3-month period should also be expected. It is also emphasised that the boundaries between the subregions are only qualitatively defined, and should be considered as transition zones rather than sharp boundaries. Consequently users of this Outlook are strongly advised to contact their National Meteorological Services for interpretation of this Outlook and for additional guidance.

Disclaimer
The information contained herein is provided with the understanding that The Caribbean Institute for Meteorology and Hydrology makes no warranties, either expressed or implied, concerning the accuracy, completeness,reliability, or suitability of the Outlook. The information may be used freely by the public with appropriate acknowledgement of its source, but shall not be modified in content and then presented as original material.

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