Once again we are watching off the SE U.S. coastline for subtropical or tropical development, this time from invest 94L which came out of the Caribbean, didn’t develop there, but now has a good chance of becoming tropical storm Beryl sometime tomorrow. I haven’t been able to post here on this yet, but if you follow my facebook page, earlier this week we discussed briefly the setup that could lead to this, as improbable as it is to have two storms like this develop in May. Once again we have an upper trough over the SE U.S. that is moving out over the water and will eventually stack up vertically with the surface low, lowering the wind shear and allowing warm-core transition. The models are in good agreement on at least some development occurring, with the exception of the GFS which may have initialization issues. As a deep trough digs into the western U.S., the same trough that is dragging Hurricane Bud towards Mexico, the deep-layer ridge currently over the southern Mississippi Valley will propagate northeastward and block 94L from escaping out to sea. The SW to NE orientation of this ridge will force 94L to turn back towards the southwest and likely make landfall in northern Florida or Georgia, a rare place to get a tropical cyclone landfall, but this is a setup that can make it happen.
This storm is different than Alberto in that it is of more true tropical origin, and it is much larger. For this reason, the models are picking up on it better than they did with Alberto. There is a large moisture shield associated with the system which 94L will be able to tap into for the next couple of days, and low-level moisture over the southeast U.S. is at a higher level than it was when Alberto formed. Subsidence from the big ridge in the south has made the mid-levels quite dry, and dry air entrainment will likely be a limiting factor in 94L’s development, but I think not as limiting as it was with Alberto. 94L will be moving over 27C waters in the Gulf Stream before making it to the coast, which should allow it to strengthen into a moderate tropical storm of around 60mph, the same peak as Alberto, but in reality a stronger storm because of its size and larger pool of moisture. SSTs do drop off a bit in the shallow coastal waters, and this combined with dry air entrainment may cause 94L to weaken just before landfall. A wildcard to consider is that landfall will be occurring in that very curved portion of the SE U.S. coastline, and such curvature can enhance convergence into the core of a tropical cyclone and help spin it up as it nears the coast.
Overall, 94L has a high chance of becoming tropical storm Beryl likely sometime tomorrow, and will be making landfall on the U.S. coast, likely somewhere between Daytona Beach and Savanna, GA. The landfall location will be pinned down better once the system has developed and starts moving towards the coast. This will be a decent rain event for Florida all the way up through the Carolinas, as the system will be turning northeast eventually as the blocking ridge moves out of the way. We may even have to watch for some redevelopment if the center gets back out over the water off of the Carolinas before moving ENE out to sea. In general this system should bring mostly good things to the SE U.S. in the form of drought relief, but tropical storm conditions will affect those near the landfall location.
After 94L, the Atlantic should be quiet for at least the next couple of weeks, as the pressure pattern over North America is becoming unfavorable to support low-level convergence in the early-season tropical breeding grounds, and we should see a lull in activity until the 2nd half of June. I will talk more about that later.
We shall see what happens!