Monthly mean SLP anomalies are analyzed from the 1958--1997 record covering the Mediterranean Basin. From point-correlation technique, a significant winter anomalous SLP oscillation between North Africa (NA) and West Asia (WA) or NAWA, is identified. Insight into the inter-annual variability of NAWA is obtained from the detrended and composited patterns. During P/N, positive/negative values of the index, higher/lower SLP values over the Mediterranean and lower/higher values east of the Caspian Sea are displayed respectively. In both cases, maximum SLP gradients are found over the Eastern Mediterranean (EM). During P/N phases, decrease/increase in winter rainfall amounts and cooler/warmer temperatures are found and could be associated with enhanced northerlies/southeasterlies over the EM. The original and undetrended NAWA indices display mostly P phases during the second half of the period. The regional trend of NAWA index could explain increased drought processes in the EM after the late 70s, in relation with northern hemispheric circulation.