While La Nina may be in a weakening phase, the ENSO state remains the dominant forcing parameter for the 500 MB weather pattern as the MJO remains basically in a neutral state. There are some signs of a period of very weak phases in phase 3 today and phase 1 by August 17th, but the signal is so weak that La Nina’s influence will mask any shift. With tropical forcing in this state, the Subtropical jet stream should remain weak throughout the middle of August, if not longer. This would suggest that once the Sahara dust dissipates, there won’t be any other inhibiting factors for developing activity in the Tropical Atlantic.
As far as the 500 MB pattern over North America, with La Nina dominant and the MJO a non-factor, we’ll be keeping a careful eye on the EPO state for the rest of this Summer and into the Fall. The general idea I have right now is when the EPO goes negative, the trough over eastern Canada will dig south into the United States. When the EPO goes positive, the western Atlantic ridge will build to the East coast, and hot and humid conditions, like now, will build into the region. I expect this theme back and forth through this month and into September, although Polar air masses will become stronger each week.
