If you’re like me, you’re tired of Isaac overstaying his welcome on our weather scene, as we’ve been talking about Isaac as a tropical disurbance, hurricane or remnant low for about 2 weeks. What was once Hurricane Isaac has split into two spinning pieces, one over the Ohio Valley and another over the Southeast. This has further complicated any efforts to forecast where rain will fall each of day, as the banding of moisture has become more disorganized with each passing day and also become largely diurnal, or surging with daytime heating and weakening with overnight cooling. Still, there is enough tropical moisture and rotation aloft for scattered showers and thunderstorms to pop up the next couple of days, and probably longer, with a few storms dumping heavy rain amounts and some storms maybe becoming severe, with localized damaging downburst winds the main threat. The chance for a widespread dump of general rain has passed, but just as has happened the last 3 days, some spots will get bonus rains while other spots get little or nothing.
While Isaac will be gradually absorbed into an eastern U.S. trough, it will be difficult to shake the current pattern of scattered tropical-enhanced showers and storms until a significant cold front can scour Isaac’s remains entirely out. That looks to happen this weekend, as a rather strong Canadian front pushes into the soupy air mass. This may increase showers and storms on Friday or Saturday as it pushes through, and will likely bring at least somewhat cooler weather by early next week, though how much cooler is a bit uncertain. The weather map for Sunday morning shows the front pushing through Virginia and the Carolinas, and it also shows what is likely to be Hurricane Leslie off the coast of the Northeast. Most likely, Leslie (a tropical storm as of Sunday night), after running over or close to Bermuda late this week, will get caught up in faster upper level flow and stay to the east of the U.S., possibly affecting Newfoundland. There is a small chance Leslie could get pulled inland by an upper-level trough over the East and affect New England. In any event, Leslie’s counterclockwise flow will help the flow of cooler, drier air from Canada southward toward us for a few days. Isaac, after 2 weeks strutting on our weather stage, will finally be forgotten.