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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 Central America for

May to July 2009

The trimester (MJJ) is usually characterized as a transition period between the dry  and wet season. While the greater part of  May is usually dry, several bouts of rains can occur towards the end of May. The transition to the wet season usually becomes complete by June.

Weather systems which can produce rainfall for the region are tropical waves and upper level tropical systems. A northward intrusion from the Inter tropical Convergence Zone(ITCZ) can  cause a sudden surge in rainfall especially over southern Belize.

Climate model forecasts from the International Research Institute (IRI) suggest the Nino 3.4 region of the eastern Pacific continues to be in the neutral phase of the ENSO cycle. Probabilities for the persistence of  this phase of the ENSO cycle remain near 80% during the trimester April-May-June(AMJ).Model forecasts suggest the  likely persistence of ENSO neutral conditions to the end of 2009. Sea surface temperatures(SST) over the tropical Atlantic continue to be slightly below normal. The trend is for  the SST to remain below normal during the trimester MJJ.

Tropical cyclone forecasts issued by the pair of Professor Gary/Klotzbach from Colorado State University (CSU) as of April suggest an average hurricane season. The current forecast calls for twelve(12) tropical storms of which six(6) will become hurricanes and two(2) become intense hurricanes. The two scientists also prepared a list of analogous years. These  years are previous hurricane seasons where atmospheric conditions appeared similar to that of 2009.The current analogous years are:1951,1968,1976,1985 and 2001.Another seasonal forecast for the 2009 hurricane season issued by the Tropical Storm Risk(TSR) group from the University of London suggests fifteen(15) named storms, of which eight(8) will become hurricanes and four(4)intense hurricanes.

Precipitation    

Tercile probability forecasts for the country are all suggesting rainfall amounts to be in the Normal (N) range with a  strong tendency for  rainfall to reach the Above Normal(AN) category this trimester. This scenario will be most probable over northern and central Belize. Rainfall amounts in the north and west will range between 150-170mm with a peak near  200-220mm for central Belize. In the south rainfall amounts will peak near 500mm.

Analogous years

Analogous years considered for this seasonal forecast are based on values similar to 2009 for the Oceanic Niño Index(ONI) for the Niño-3.4 region .These years are: 1990,1980,1979,1961 and 1952.

Prepared by: Frank Tench Jnr. (weather forecaster)

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