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The Precipitation Outlook for the Caribbean is prepared by the Caribbean Institute for Meteorology and Hydrology with contributions from the regional Meteorological Services and the Climate Research group at UWI, Mona.

The precipitation outlook provides probability distributions indicating the likelihood of below-, near-, or above normal rainfall for the various sub-regions of the Caribbean. For this purpose, ‘normal’ is defined as the climatological mean. The Outlook is generated through analysis of historical records throughout the region, data available from the global climate monitoring system, and computer models of the evolution of the global sea surface temperature field.

The outlook is produced by combining objective input (dynamic model output) and subjective input (experience). The process starts with an examination of the sea surface temperature and precipitation forecasts from the climate models. Currently the output from four climate models are examined; three - ECHAM, CCM3, NCEP - from the International Research Institute for Climate Prediction (IRI) and one from the United Kingdom meteorological Office (UKMO). Tercile probabilities are then estimated for a number of sub-regions based on:

• Forecast anomalous precipitation from the IRI models

• Probabilities from the UKMO model

• The level of agreement between the models

• Subjective confidence in the model forecasts based on current conditions in the region and knowledge of the local climatic conditions

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

• Above normal - wettest third of the record
  

• Near normal - middle third of the record
  

• Below normal - driest third of the record
  

The tercile probabilities are presented in the form:

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 emphasized that the boundaries between the sub regions 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

Precipitation Outlook for Caribbean April - June 2008

Precipitation Outlook for Central America for

August 2008 to October 2008

The trimester (ASO) is usually characterized as the second part of the rainy season. Most stations receive their most rainfall during the final two months (Sept, and Oct.) of the trimester. August for the greater part, represents a temporary lull in the rainy season.

The trimester (ASO) is also the most active part of the hurricane season,  with the peak period for tropical cyclones occurring around Sept. 10^th. The seasonal forecast from Colorado State University (CSU) is once again calling for an “above average” hurricane season. Together with seasonal forecasts from the National Oceanographic and Atmospheric Administration (NOAA) and the Tropical Storm Risk (TSR) group, all three groups have issued forecasts which tend to agree on an active hurricane season.

Climate model forecasts from the International Research Institute (IRI) suggest the Nino 3.4 region of the eastern Pacific remains in the neutral phase of the ENSO cycle. Probabilities for the persistence of the neutral phase of the ENSO cycle remain near 60% during the trimester (ASO).

Weather systems which can impact on the rainfall for the Caribbean and Central America are tropical waves, upper level lows and tropical cyclones. Tropical storm Arthur formed over northern Belize on May 31^st, before dissipating to a tropical depression the following day. The odds for another tropical cyclone to impact the Caribbean appear quite high. One or two cold fronts are also possible during the months of September and October.

Precipitation    

Rainfall patterns for the year suggest most stations have been receiving rainfall amounts near their normal values. Tercile probability forecasts for the country are all suggesting rainfall amounts in the Normal (N) range for this trimester. There is a slight probability for rainfall in the  north and the extreme south  to waver below normal(BN).Rainfall amounts will range from 168mm  in the north, between 200 and 250mm over inland and coastal areas and near 600mm in the south.

Analogous years

Analogous years considered for this seasonal forecast are based on values similar to 2008 for the Oceanic Niño Index(ONI) for the Niño-3.4 region .These years are 1976,1989 and 2000.

Prepared by: Frank Tench Jnr. (weather forecaster)

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