Interannual variability of the midsummer drought in Central America and the connection with sea surface temperatures

Abstract

Abstract. The midsummer drought (MSD) in Central America is characterised in order to create annual indexes representing the timing of its phases (start, minimum and end), and other features relevant for MSD forecasting such as the intensity and the magnitude. The MSD intensity is defined as the minimum rainfall detected during the MSD, meanwhile the magnitude is the total precipitation divided by the total days between the start and end of the MSD. It is shown that the MSD extends along the Pacific coast, however, a similar MSD structure was detected also in two stations in the Caribbean side of Central America, located in Nicaragua. The MSD intensity and magnitude show a negative relationship with Niño 3.4 and a positive relationship with the Caribbean low-level jet (CLLJ) index, however for the Caribbean stations the results were not statistically significant, which is indicating that other processes might be modulating the precipitation during the MSD over the Caribbean coast. On the other hand, the temporal variables (start, minimum and end) show low and no significant correlations with the same indexes.The results from canonical correlation analysis (CCA) show good performance to study the MSD intensity and magnitude, however, for the temporal indexes the performance is not satisfactory due to the low skill to predict the MSD phases. Moreover, we find that CCA shows potential predictability of the MSD intensity and magnitude using sea surface temperatures (SST) with leading times of up to 3 months. Using CCA as diagnostic tool it is found that during June, an SST dipole pattern upon the neighbouring waters to Central America is the main variability mode controlling the inter-annual variability of the MSD features. However, there is also evidence that the regional waters are playing an important role in the annual modulation of the MSD features. The waters in the PDO vicinity might be also controlling the rainfall during the MSD, however, exerting an opposite effect at the north and south regions of Central America.

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“…This pattern characterizes the midsummer drought phenomenon, which occurs throughout Central America (Maldonado et al. ). The seasonal curve of precipitation shows the midsummer drought followed by a larger spike of precipitation in the second part of the wet season, ending in late October or early November.…”

“…1). This pattern characterizes the midsummer drought phenomenon, which occurs throughout Central America (Maldonado et al 2016).…”

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“…The MSD intensification shows also a strong correlation with the iCLLJ and the iTAP (see Figure e,f); as the Pacific Ocean warms (see Figure g), and consequently the CLLJ intensifies (see Figure ), it leads to a reduction in precipitation during the MSD season in agreement with previous works (Small et al ., ; Amador, ; Rauscher et al ., ; Fuentes‐Franco et al ., ; Maldonado et al ., ). For an intensified (weakened) CLLJ we could expect an increase (decrease) of the MSD intensity.…”

“…For example, Maldonado et al . () suggest that the characteristics of the MSD may be better defined using daily data, because a MSD condition could occur within a month's period.…”

“…By using monthly data we recognize that this could limit the results of our work. For example, Maldonado et al (2016) suggest that the characteristics of the MSD may be better defined using daily data, because a MSD condition could occur within a month's period.…”