Good evening! I wanted to post a (relatively) quick blog update tonight; not much has changed in the overall thinking with Tropical Storm Isaac since last night's update. While the storm is over some very warm water in the northern Caribbean -- and there is much warmer water to come to the west -- it is a poorly organized system with the mid level circulation separated from (several) low level circulations. In other words, while Isaac may look somewhat impressive on satellite, with lots of high, cold thunderstorm tops and better outflow, it's more bark than bite as the tilted nature of the system is preventing it from strengthening. There is also some dry air being ingested into the system; a recent upper air sounding (weather balloon data) found a lot of dry air between 12 and 16,000 feet over Puerto Rico. Northwest wind shear is helping to bring this dry air into the center of Isaac, further disrupting its attempt to organize.

There was a turn toward the west-northwest with the motion of the storm today and, as expected, it has slowed down. That west-northwest heading will continue though as long the storm remains relatively weak; remember from yesterday, a weaker storm will tend to track farther west while a stronger storm (earlier) will track farther north. The European model continues to show a very poorly organized system tracking across the south coast of Cuba and into the central Gulf where, ultimately, it becomes a significant hurricane. Meantime, the GFS (American) model shows a stronger storm earlier than tracks a bit offshore the west coast of Florida. The European track would be one that would not impact Florida very much aside from some breezy weather and above average tides for a couple of days while the GFS track (which we still favor) would bring more significant impacts to Florida in the form of squally weather with isolated severe storms (especially west) starting late Sunday through Tuesday. Any adjustment farther to the west though is a good thing for Florida, as it means less in the way of impact on the peninsula.

Tonight will be critical. A break is located in the the ridge north of Isaac; if Isaac can organize more overnight, it will tend to turn more toward the north and have a better chance of impacting Florida is a more significant way. If Isaac remains poorly organized, that will lend more support to the more westward European track. The hurricane hunters will continue to fly low level missions through Isaac every 6 hours. Earlier today, a NOAA Gulfstream plane sampled the upper atmosphere to the north and west of Isaac and this additional data will go into our computer models that start running at 8pm/Thursday. This will give us a much better idea on the future track of Isaac; tonight is critical!

Brian Monahan