Forecasting a tropical storm is very difficult until it matures and a steering pattern can be established. With Erika, we just don't know when that will be. The storm is disorganized and about 100 miles off track from the exact spot it was forecast to be just 24 hours prior. It's interesting to note, however, that the storm was still within the cone of uncertainty that was released at that time. As of the Thursday 5 pm advisory, Tropical Storm Erika was located west of Guadeloupe and southeast of Puerto, producing winds up to 45 mph and moving west-northwest at 15 mph. Forecasters with the National Hurricane Center have noted multiple times that confidence is very low on what Erika might do when and if the storm approaches Florida, saying "potential impacts for the Bahamas and beyond are unusually uncertain".
Not much has changed with the structure or strength of the storm, as it is still very disorganized. Visible satellite imagery and hurricane hunter data continued to indicate that the low-level center of circulation was well displaced from the thunderstorms and higher wind gusts. This was occurring because winds aloft are particularly strong and shearing those storms apart. Until the thunderstorms can persist near the center of the storm and wrap entirely around it, Erika will continue to be weak and prone to falling apart entirely.
Wind shear is presently preventing Erika from strengthening. If the storm moves over the mountainous islands of Puerto Rico and Hispaniola, the interaction with those land areas could significantly reduce its strength. However, if it can survive on its journey through the Greater Antilles, an environment much more favorable for strengthening awaits near The Bahamas. Water temperatures are very warm and the wind shear is expected to be much lighter in these areas when Erika potentially arrives Sunday. For these reasons, how strong Erika could be when it nears Florida ranges anywhere from a meager tropical storm like it is now, to potentially a formidable hurricane. While forecast tracks of tropical cyclones have improved in recent years, the intensity forecasts are still very challenging.
When (or if) Erika matures will play a huge role in where it moves. A weaker storm would tend to move more on a westward track, being steered by the trade winds out of the east. A stronger storm, however, would extend further up in to the atmosphere and be turned northwest by upper-level winds moving clockwise around an area of high pressure in the western Atlantic. Until the storm strengthens, though, it may tend to move further west (or left) of it's original forecast track. This would force it to move through or over the larger islands of the Greater Antilles and further complicate both the intensity and track forecast.
Needless to say, the situation is not any clearer than it was 24-hours ago. It may not be until the storm nears or passes through the island chain that we gain a better understanding of where Erika is moving and strong it could be at any given location along its way. That would be late Friday or Saturday. The Florida Public Radio Emergency Network will continue providing updates to all Florida public media stations, both on the air and online via each station's websites and social media accounts.