Tropical Storm Erika is now centered about 300 miles east of the Lesser Antilles, and it is moving quickly to the west at 17 mph. As far as the next couple of days goes, Erika will continue to make its way into an environment that has a strong wind shear and dry air; both of which are inhibitors for strengthening of any tropical system.
This system will possibly face a lower magnitude of wind shear and dry air than Hurricane Danny did, but with counterproductive conditions and a potential track over land in the Caribbean can complicate the intensity and track forecasts.
The Air Force has been closely monitoring the situation, and data does indicate that the surface pressure has dropped and the convection has been pulsing near the center, which is typical behavior during the nighttime for a tropical cyclone.
Erika is a fast moving system, and it is predicted that it will arrive in the northern Leeward Islands Wednesday night or early on Thursday. Storm-force winds and heavy rain will be the greatest risks with Erika, and this has prompted some tropical storm warnings to be issued for the northern Leeward Islands. This is the second time in less than three days that a tropical storm will make its way into the Leeward Islands, as Tropical Storm Danny did earlier this week.
More than likely, more tropical storm warnings will be issued throughout the day on Wednesday; especially if Erika continues to strengthen as predicted. No matter what track this storm takes, it will definitely bring the rain and wind to drought-stricken Puerto Rico, as well as the Virgin Islands by Thursday.
When talking about a longer term forecast, it is still uncertain due to the fact that this system has the potential to track over land in the Caribbean, will possible interact with some wind shear, and the fact that there is an upper-level flow near the eastern U.S as we move into next week.
The southern dip in the jet stream in the East that is responsible for the cooler dry air in the Midwest and Northeast would certainly curl any tropical system away from the U.S East Coast. Unfortunately, that pattern does not look like it is going to hold.
This southward dip will be replaced by a northward-migrating stream into eastern Canada and northern New England. Any leftovers of the southward dip will be much weaker and farther to the West, meaning that it will not impact Tropical Storm Erika much if at all.
There is also a Bermuda high taking place southwest of Bermuda, and this isn’t necessarily a pattern that will keep Erika away from U.S shores next week. If this system continues to strengthen as planned, it could get pulled to more of a northwestern track, and could be susceptible to a potential steering pattern.
If Erika starts to weaken, it would track farther to the west and south along the southern edge of the forecast path and may get broken up as it moves over land. Or, what could happen is that Erika downgrades to a tropical wave due to wind shear, as was Tropical Storm Danny.
We are still about five days out (or more) from any potential for Erika to hit the U.S East Coast. The average forecast track error of a National Hurricane Center five-day forecast is about 241 miles. It can also be difficult to track the intensity of tropical systems such as this, and we saw this exact situation with Danny.