Tropical Storm Erika is a mess today, barely holding itself together as it draws closer to Puerto Rico. Despite its ragged appearance, the storm is producing very heavy rain along its path; devastating flooding on the small island of Dominica killed at least four people last night. Erika is still a threat to Florida, and current forecasts show the storm closing in on the Sunshine State as a hurricane early next week.

As of the 5:00 PM EDT advisory, Tropical Storm Erika has 45 MPH winds as it moves toward the west-northwest, which puts its eventual track closer and closer to the tall mountains of Hispaniola and Puerto Rico. These islands have a nasty habit of destroying storms as they pass overhead, so there’s a real possibility that Erika won’t survive to the other side of the Greater Antilles. It’s such a short distance either way that it’s impossible to tell exactly what will happen until it actually happens.

The latest forecast shows the storm—assuming it survives—moving into the Bahamas and strengthening into a hurricane as it approaches Florida. The track uncertainty at this point is very high, so the storm could wind up anywhere from Cuba to the Carolinas or even out to sea. The forecast indicates general direction at this point—we’ll worry about its exact track this weekend. Anyone in or around the cone of uncertainty should be concerned, though, and it’s a good idea to start gathering supplies and revising plans just in case you come under threat.

Above is the probability of tropical storm force winds according to the National Hurricane Center—warmer colors indicate a higher risk of encountering tropical storm conditions over the next five days. This will change as Erika strengthens or weakens and as forecasters refine the track, but it gives you a good idea of the risk as it stands right now.

For its entire life, Erika’s looked like a storm that stumbled out of bed with the flu—save for a few rare occasions, its center of circulation has been completely removed from its thunderstorms, and the convection itself is throbbing between virtually nothing and deep torrents that reach the top of the troposphere.

The culprit behind the tropical storm continuous struggle is dry air and wind shear, the latter of which is having more of an effect these days. Wind shear prevents thunderstorms from organizing around the storm’s center of circulation, blowing them downstream and keeping the system from strengthening.

Weaker storms tap into a different current of winds than stronger storms, so Erika’s track is directly related to its strength. Since it’s stayed on the weaker side, the storm is caught in low-level easterly flow pushing the center farther and farther west than originally forecast.

Even though Erika is a marginal tropical storm at best, the system is a prolific rain producer. The small island of Dominica got stuck under the heaviest rain in the storm, producing devastating flash flooding that killed at least four people and caused untold amounts of damage. The Associated Press also reports that parts of the island received up to fifteen inches of rain last night, which is an incredible amount of water in such a short period of time. It doesn’t take a strong storm to create a disaster.

Puerto Rico is now in the line of fire for very heavy rain and gusty winds as the storm crosses the island tonight and tomorrow. Much of the island stands to see several inches of rain from the storm, and locations at the foot of hills and mountains could see much higher totals. The rain will help with the drought, but too much rain all at once will lead to life-threatening flash flooding and landslides—scenes like the one that played out in Dominica today would create a much larger disaster in Puerto Rico, and island that’s home to fifty times more people than the former.

The future of Tropical Storm Erika is highly uncertain. Don’t ignore the threat, even if you’re not in the cone of uncertainty. Keep a close eye on the forecasts, and make sure you’re prepared for this and any storms in the future. Gather food, water, batteries, candles, flashlights, fuel, medicine, first aid supplies, and cold hard cash now just in case the storm hits and you’re stuck without power or water for several days. If you do it now, you won’t be caught in the mad rush on grocery stores if/when the storm gets closer to land.

The next full forecast from the National Hurricane Center comes out at 11:00 PM EDT.

[Images: NOAA, author | Video: CBS News via YouTube]

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