Isaac is back. Well, the partial remnants of the former hurricane, that is. After a seven-day trip over land in the central and southern part of the U.S., Isaac’s remnants have now moved back over the warm waters of the Gulf of Mexico, entering through Mobile Bay Wednesday morning. The boomerang-like path Isaac has taken is a result of weak steering currents over the central part of the country and a clockwise flow of air around high pressure over the Southern Plains. While it’s not unusual for a storm to make some wild turns and reverse directions, doing this after nearly a week over land is rare.
Thunderstorms with heavy rain continued to develop near Isaac’s remnants and have recently doused parts of the Florida panhandle with over five inches of rain in the past two days. This came after more than two dozen tornadoes that were spawned from the tropical system over the lower Mississippi River valley and parts of the Ohio Valley. Needless to say, Isaac’s post-landfall impact has already been significant. And, it may continue for several more days.
Upper-level winds are forecast to be weak enough to allow the remaining energy and moisture from Isaac to stall over the wam waters of the Gulf of Mexico. Environmental conditions appear marginally favorable for tropical development over the next 48 hours, and the National Hurricane Center has identified the disturbance as Invest 90L. Plenty of uncertainty exists in the forecast for what may become Tropical Storm Nadine over the coming days, so stay tuned for future updates.
Whether or not 90L (or Nadine) develops into a tropical cyclone may be a moot point. A cold front is forecast to pick the system up and steer it across the state of Florida over the weekend, at which time its window for strengthening would have closed. Either way, there are some certainties to our weekend forecast, which includes a good chance for showers and thunderstorms, with a few episodes of heavy rain possible. The arrival of our first fall cold front is also something we are now much more confident on. Forecast data suggests a a ridge of high pressure originating in Canada will move all the way into the Southeast U.S. by next Tuesday. High temperatures will likely fall into the lower 80s and overnight lows are forecast to dip well into the 60s by the middle of next week.