Spatial variability of the Caribbean mid-summer drought and relation to north Atlantic high circulation

Abstract

Annual rainfall in the Caribbean exhibits a bimodal structure with two rainfall maxima (May-June and September-October) separated by what has been termed a mid-summer drought (MSD) (July-August). Despite general acceptance of the intensification and expansion of the North Atlantic High Pressure (NAHP) as the cause of the Caribbean MSD, it has been noted in several studies that the influence of the NAHP may not be consistent across the region. The purpose of this research is to better understand the Caribbean MSD by mapping the spatial co-variability of the Caribbean MSD and then determining the association between these spatial patterns and NAHP circulation. The spatial variability of the Caribbean MSD is identified through mapping of Principal Component Analysis (PCA) loadings of Caribbean MSD season rainfall time series. A correlation analysis was completed between monthly MSD region rainfall time series and measures of the NAHP to assess the degree of association between the spatial variability in the Caribbean MSD and NAHP circulation. The PCA identified six MSD regions, the northwestern Caribbean, the interior Caribbean, the eastern rim Caribbean, Coro Venezuela, Grantley Barbados, and a transition zone. The spatial pattern of the MSD regions suggests that the NAHP impacts the eastern Caribbean first and then progresses westward as the summer develops. In regard to the association between NAHP circulation and MSD region precipitation time series, correlation analysis indicates that overall, a modified Bermuda High Index (BHI) is a more effective tool in evaluating the association between the NAHP and Caribbean MSD as compared to the traditional indices, NAO EOF and BHI. Lagged correlations support previous findings that the winter preceding a particularly dry summer in the Caribbean is characterized by a strong pressure gradient on the southeastern flank of the NAHP; implying stronger Trade Winds, cooler sea surface temperatures, and reduced convective rainfall.

Impacts of Urban Development on Precipitation in the Tropical Maritime Climate of Puerto Rico

“…Wetter regions occur on the northern side of mountains that shield the southern drier region from Atlantic moisture. Precipitation in Puerto Rico shows a yearly cycle with a bimodal distribution (two maxima) peaking first in May as the wet season starts followed by the "Mid Summer Drought" [43] and then a second and biggest peak in October-November, consistent with patterns across Central America and the Caribbean Basin [25,33,36,39,44,45]. Mean annual temperatures range from 22 °C to 25 °C [42].…”

Climate impacts of recent multidecadal changes in Atlantic Ocean Sea Surface Temperature: a multimodel comparison

“…This co-incidence suggests that these minima may result from a saturation of the local precipitation response which is not seen in the other models. 2 The rainfall mid-summer minimum, or Mid Summer Drought (MSD), is thought to be a consequence of a westward extension of the North Atlantic Subtropical High (NASH) pressure system over the Caribbean region Gamble et al 2008). (1951:1960) and (1961:1990).…”

Cloud-to-ground lightning over Mexico and adjacent oceanic regions: a preliminary climatology using the WWLLN dataset

“…5b) starts in May and ends in December, the period that corresponds to the rainy season for this area. Annual rainfall over the Caribbean exhibits a bimodal structure with two rainfall maxima (May-June and September-October) separated by what was termed a mid-summer drought, occurring in July and August (Gamble et al, 2008;Magaña et al, 1999). The seasonal cycle of lightning, showed in the Fig.…”