Precipitation variations during the recent SST warming period in the Intra-Americas Region, 1982–2012

A recent warming trend of sea surface temperatures (SST) has been detected in the Intra-Americas Region (IAR) for the past 30 years (1982-2012), which could have potential implications for precipitation variation within the Caribbean and the surrounding region. The IAR, defined as the geographical region that includes the Caribbean, Mexico, Central America and parts of North and South America, is a region of distinct climatological activity. Using the National Oceanic and Atmospheric Administration (NOAA) Optimum Interpolated Sea Surface Temperature (OISST) product, 30-year trend analysis and linear regression was completed for the years 1982 - 2012. Time series of regional averages show that SSTs are increasing annually and seasonally for the IAR during the 1982-2012 period. Annual average trends reflect an increase in regional SSTs of 0.015 °C per year, slightly faster than the annual global rate of 0.011°C per year. The two Caribbean rainy seasons, the Early Rainfall Season (ERS) from April to July and the Late Rainfall Season (LRS) from August to November, reflect estimated trends at 0.01°C per year and 0.02°C per year respectively. Furthermore, sub-regional analysis revealed that SSTs increases are more pronounced in the Gulf of Mexico and North of South America during the ERS and LRS. Increases in SSTs during the LRS are of particular importance because temperatures during this season reach 26°C and above, which is the threshold for deep convection. Within this temperature range, the atmosphere becomes the principal modulator of thermal convection. In this way, SSTs influence Tropical precipitation.

The precipitation analysis, using the Global Precipitation Climatology Project (GPCP) monthly precipitation dataset, shows that the past 15 years (1995-2010) average precipitation for the LRS has been slightly above the climatology calculated from the year 1979 to 2010. Results suggest that the observed increases in SSTs may be connected to the changes in precipitation for the same period. SST daily anomalies reflect a larger warming trend over the past 15 years, which further suggests the significant influence that SSTs potentially have on precipitation. During the ERS, warming SSTs in the region North of South America and above the threshold for vertical convection were found to be highly cross-correlated (0.79) with precipitation. For the LRS, cross-correlation with precipitation and the SSTs near South America also show a high, positive cross-correlation (0.78), similar to ERS results. Our results show that the positive correlation is potentially marked by an increase in precipitation over the latter half of the period (1995-2010).