Tropical Storm Isaac formed from a strong easterly wave that left the African coast back on August 16th. It became the season’s ninth Tropical Depression this past Tuesday morning, then just twelve hours later was upgraded to the season’s ninth Tropical Storm: Isaac. It has had a history of battling some dry air, which puts a brake on its strengthening, and today is no exception. While it is certainly more robust overall, some vertical shear and dry air are keeping it from getting very strong. As of 2pm this afternoon, the maximum sustained winds were 45mph, and it’s now passing over the island of Guadeloupe in the Leeward Islands.
There are some radar loops of Isaac already available here, and more will be added as it passes by other radar sites. It is also under near-constant reconnaissance by the NOAA and Air Force planes, so any changes in intensity will quickly be assimilated into the National Hurricane Center‘s analysis and forecast.
Model guidance continues to put southern Florida in the cross-hairs on Monday, after passing over Haiti and eastern Cuba. This solution has been consistent for a few days now, with some wobbles back and forth, but generally steady. If this is indeed the case, expect conditions to deteriorate during the day on Sunday, then Monday would be a potential landfall or at least the closest approach. If it doesn’t hit southern Florida head-on, that means it either went a little to the west and would travel up toward the northern Gulf coast, or it went a little east and would travel up toward the Carolinas. Both of those scenarios would give Isaac much more time over warm water to strengthen.
This map shows the cumulative probability of a location experiencing tropical storm force winds within the next five days given the most recent official forecast track. You can see that southern Florida is in the 20-30% bin, and that will increase as the storm gets closer. (The shaded areas on the right part of the image are for Tropical Depression 10, which isn’t going to be a concern.)
As it appears now, regardless of if Isaac hits the Miami area head-on, we can expect some adverse conditions – perhaps tropical storm, and perhaps even hurricane conditions. The exact path over the next 2-3 days will be a big factor in determining what we’ll get here. If the storm passes directly over Hispaniola and some of eastern Cuba, it will be weakened quite a bit. But in the 24 hours it has between Cuba and southern Florida, it could very well re-intensify. It would be prudent to use the next 3-4 days to prepare for the worst and hope for the best.
Brian McNoldy
Senior Research Associate
& Author of Tropical Atlantic Update
Follow Brian on Twitter: @BMcNoldy