Important as a review, is the influence on summertime rainfall patterns in South America by a semi-permanent upper-level low pressure trough located off the Southeast coast of Brazil for most years in this decade. The just-issued ECMWF “monthlies” are forecasting the presence of this low-pressure system for early-to-middle summer.

Surprising is overall success of the GFS ENS skill score of forecasting the upper air pattern (using 500 MB anomalies) during the 16-30-day period across both North and South America for the past 30-day, 14-day, and 7-day intervals. Traditionally, the ECM “weeklies” are used to make a “first guess” at the expected weather during this timeframe. ECM rivaled GFS ENS for North America forecasts and finished second to GFS ENS in South America.

Last month, the “warm blob” returned to the Northeast Pacific. However, during September the “warm blob” has lost intensity and an atmospheric river (AR) storm track into Southwest Canada this week is likely to cause further erosion.

Tropical Disturbance 94L is located over the eastern Dominican Republic this morning. 94L is encountering westerly shear and the high terrain of the Dominican Republic inhibiting development. However, if the inner structure of the system can bypass the upper shear and orography effects, development is likely by early weekend in the Southeast Bahamas. NOAA/NHC indicates 80% chance of a tropical cyclone after 48 hours.