When you see imagery depicting the MJO, which is basically an area of forcing/lifting in the tropics, there are four issues to check out before making any forecast on impacts in Canada and the U.S. One is strength of the convective field. Next is position. Thirdly, is there linkage to the polar westerlies? And, last but not least, is downwelling of the oceanic waters evident? Many times I come across comments in the weather business like, “we are in Phase 8…snow for Philly!” It is not that simple, and the sector diagrams that pop up on the Internet are usually of zero help to forecasting. And for people like traders in energy and agriculture, only add more confusion to the issue.
The position of the oscillation event often has limited relation to the tropical Atlantic Basin. We see struggling TS Philippe undergoing a merger with a circulation to its east, and being corrupted by a TUTT signature in the Caribbean Sea, As we have seen so many times this hurricane season, calls for a hyperactive, dangerous array of storms have been taken apart by shear, dry air, and oceanic cold pools. In an El Nino year, the westerlies aloft dominate, keeping the worst systems far away and ripping up those that get too near to the major population centers.
The Indian and Pacific Basins is a different story entirely. As of now the MJO is percolating with convection, but is incoherent, straddling the entire equatorial region. This may give rise to tropical systems. But most importantly, note the visible connection of the thunderstorms to the polar westerlies off around the International Dateline. A huge Kelvin wave in Southeast Asia looks to juice this linkage, giving rise to warm advection at higher latitudes. If the +PNA/-AO configuration (northern Canada ridging) develops, we will see chances for cooler weather in the eastern 2/3 of the USA by October 7-8, with the warmth redeveloping across the Intermountain Region.
Indeed, the 11-15 day period should take on a warm West vs. cool Central/East alignment, perhaps lasting through the middle of next month. Not wintry stuff, mind you; but that part of the forecast is far from settled.