Persistent easterly winds leading to precipitation in the Atlantic Coast of Patagonia

The relationship between daily precipitation and unusually persistent easterly wind recorded at station level along the coast of Eastern Patagonia is examined. Easterly wind events that persist for more than 20 h (E) are infrequent in Comodoro Rivadavia (CMR); but in about 80% of the times they do occur daily precipitation exceeds 1 mm. Although 2‐day persistent easterlies (2E) occur only about 1% of the time in CMR they are associated with 20% of the >75% percentile rain events. The occurrence of precipitation days (P ≥ 1 mm) during 2E events (P1&2E) is far from randomness for most stations. For daily P1&2E events in CMR, the convergence of westward moisture flux from the Atlantic is the key. Its daily frequency shifts towards Niño (44%), followed by Neutral 35 (32%), and Niña (25%) conditions. The probability of null precipitation days with westerlies was higher than 95% on average among the stations. The tropospheric circulation anomalous conditions associated with P1&2E events are characterized by a blocking‐like flow along 80–90°W, with anticyclonic anomalies near 60°–70°S and cyclonic anomalies in the mid‐latitudes. The strength of the anomalies is given by the meridional gradient of tropospheric circulation anomalies, stronger during the Niño phase. A P1&2E event at CMR is linked to active slow‐moving weather systems linked to tropospheric Rossby waves triggered by upper‐level tropospheric mass divergence anomalies in low latitudes. The source and trajectory these Rossby waves are different through ENSO phases. We have found that heavy precipitation over subtropical eastern Argentina during Niño precede CMR P1&2E events by 10 to 8 days. Daily P1&2E events contribute substantially to the mean precipitation total from April to June. The differential influence of the ENSO phases through the seasons of year is evident in such a contribution.