Invest 94L, a tropical wave which is located about 250 miles or so to the southwest of the Cape Verde Islands, is of significant concern to me and I will say that right up front. Latest analysis early this morning shows that shower and thunderstorm activity is gradually becoming more consolidated and is slowly increasing. Additionally, the 850 millibar vorticity chart shows that the amount of spin associated with 94L is also slowly increasing.
Invest 94L is currently tracking to the west at a forward speed of 15 to 20 mph and I expect this westward track to continue right into a majority of next week. As for strengthening, I think we will see gradual intensification and this system seems destined to become Tropical Storm Isaac by either Sunday night or during the day Monday. Beyond that, environmental conditions are favorable for strengthening throughout much of next week and I do feel confident enough to say that I think this will become a hurricane by about the middle part of next week.
The latest GFS model guidance has shifted further west with the overall track of 94L and forecasts it to significantly impact Barbados and much of the Lesser Antilles with hurricane conditions from Thursday afternoon through Thursday night and into Friday morning. After that, the GFS model forecasts future Isaac to impact Puerto Rico with hurricane conditions by next Saturday. From there, the longer range GFS model seems to suggest a track north and then northeast about halfway between the US East Coast and Bermuda during the week of August 27th.
The latest European model guidance has a much weaker system that never really closes off into a storm. This leads to a Caribbean cruiser by late next week into next weekend. Right now, given the presentation of how 94L looks and that the overall pattern in the Atlantic Basin is favorable for an intensifying tropical cyclone, I think the European model guidance forecast seems unlikely and I’m leaning much more towards the stronger GFS model forecast.
So, here are my thoughts on Invest 94L: I do think that this system poses an eventual threat to the Lesser Antilles. Given the fact that the ridge of high pressure to the north of 94L is fairly strong, I see no evidence of a turn to the northwest before it reaches the Lesser Antilles. Additionally, the fact that the intensity guidance is insistent on significant strengthening to not only hurricane strength, but major hurricane strength leads me to believe that all interests in the Lesser Antilles, as well as Barbados should closely monitor the progress of this system for you may have a hurricane knocking on your door by Thursday.
~ Rob Lightbrown, Crown Weather Services
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