Satellite image of Emily, just south of Hispaniola Thursday morning. (NOAA)

5 P.M. Update: Emily has degenerated and been downgraded from a tropical storm to a low pressure trough. It is still expected to produce copious rainfall over Hispaniola and could regenerate if/when it moves open more open water. We’ll provide an update Friday.

Earlier: Tropical storm Emily, which has changed little in strength for two days, is closing in on the island of Hispaniola, which encompasses Dominican Republic and Haiti. At 11 a.m., it was positioned 90 miles south of Port Au Prince, Haiti. Heading west northwest at 5 mph, maximum sustained winds are 50 mph.

Tropical storm warnings are in effect for much of Hispaniola, a section of eastern Cuba, the southeastern and central Bahamas and the Turks and Caicos. A tropical storm watch covers the northwestern Bahamas.

For now, the primary concern with Emily is its potential impacts on Haiti where more than 600,000 people reside in tents following the January 2010 earthquake. The storm’s copious moisture and slow motion have led the National Hurricane Center to predict 6 to 12 inches there, with isolated amounts to 20 inches. Life threatening flash floods and mudslides are possible.

Through 10 a.m., no rain had fallen in Port Au Prince according to Miami Herald correspondent Jacqueline Charles, but it is expected to begin shortly.

What are Emily’s long-term prospects? Let’s begin by assessing its current health...

How does Emily look now?

Though Emily appears a little more structured this morning, with the clusters of thunderstorms closer to the low-level swirl than in recent days, it remains a disorganized tropical cyclone. The storm is apparently fighting destructive interference from a Saharan Air Layer just to its northeast (though perhaps not as much as in recent days), the rough terrain of Hispaniola, and an easterly trade wind that continues to push the low-level vortex westward faster than the thunderstorms.

Track forecast

Because Emily’s circulation appears to be concentrated at low levels, the easterly trade winds are largely controlling the storm motion for now. The northward turn, advertised by many of the track models, has not yet materialized.

The models that keep Emily a weak storm prefer a west-northwestward course for the next day or so before hinting at either a northward curve over Cuba or a more permanent west-northwestward track towards the eastern Gulf of Mexico (before ultimately hooking back to the east). This would put south Florida in Emily’s cross hairs.

Model track forecasts for Emily. Plot provided courtesy of Jonathan Vigh, Colorado State University. For more information about this graphic, click here.”

Regardless, one of the key players determining where Emily will go is how strong it’ll get. The latest track guidance appears split into two clusters; one that crosses western Hispaniola on a northwestward path toward the Bahamas, and another that continues Emily west-northwestward toward the Florida Keys.

If Emily passes south of Hispaniola today before making the turn, the likelihood of a Florida impact –as a weak system- meaningfully increases. Such a scenario would be a good thing for Haiti, reducing the rainfall output there.

Intensity forecast

Emily still has a lot of maturing to do before it can intensify much further. This is especially true given its proximity to the rough terrain of Hispaniola and Cuba, and the not-so-friendly environmental conditions around it. Given these observations, the weaker/more westward track over the next two days is a realistic outcome. And though the prognosis becomes exceedingly uncertain beyond that, the current trend suggests the southeast U.S.Coast, in particular Florida, is not out of the woods yet.

On a more north and easterly track, some models still indicate Emily could attain hurricane status - but that’s contigent on the storm surviving the treacherous trip over Hispaniola.

Impacts on the Southeast and mid-Atlantic U.S.

Under the southern track scenario, south Florida and the Keys would potentially contend with heavy rain, high surf, and gusty winds, but unlikely a destructive storm. If the storm turns to the northeast, the Atlantic coast from south Florida to the mid-Atlantic would most likely deal with elevated surf and some rip currents during the weekend and into early next week, rather than a direct hit. Around the mid-Atlantic, since a direct hit with rain and wind looks unlikely, no need to change beach plans at this point... but continue to stay tuned.

Here’s a video we just produced describing the scenarios for Emily...

Related: 2011 Hurricane Tracking Center