Tropical Storm Melissa was churning over the sultry waters of the southern Caribbean Sea early Wednesday and is expected to take a slow turn northward through the end of the week, eventually becoming a hurricane.
Hurricane watches cover southern Haiti, including Port-au-Prince, while a tropical storm watch is in effect for Jamaica.
There's still a chance that Melissa remains far enough south and west to spare the islands of the worst impacts, instead dumping most of its rain over the ocean and veering toward Central America. Track forecasts for Melissa continue to be more uncertain than normal because of the weak steering currents.
Although direct impacts from Melissa are unlikely in the United States, people along the East Coast should keep an eye on the storm - especially if it lingers in the Caribbean Sea for a long time, as that could lead to a more unusual storm track next week.
As of Wednesday morning, Melissa had winds of 50 mph and was crawling west-northwest at 2 mph, about 305 miles south of Port-au-Prince, Haiti.
The storm was traversing exceptionally warm ocean waters, in the upper 80s, which would normally fuel elevated concerns for rapid intensification. But the system is lopsided, knocked off-kilter by disruptive shear, or changing winds with height. That shear has blown most of the convection, or thunderstorm activity, east of Melissa's low-level center.
Forecasters call that pattern the "Caribbean graveyard"; it has spelled the demise of many hurricanes. That harsh shear, coupled with somewhat dry mid-level air on the west side of the system, are limiting how much Melissa can strengthen. Even five days from now, the National Hurricane Center forecasts the storm will be at a Category 1 strength.
But the longer Melissa remains over ocean waters with such extreme heat content, the higher the chance that the storm will intensify.
Melissa could bring significant and prolonged impacts to the northern Caribbean islands because of its forecast slow movement.
Meteorologists have high confidence in a very slow west-northwestward or northwestward movement in the coming days. In fact, Melissa may even stall. Ordinarily, a parked hurricane would weaken itself by churning up cooler ocean waters below. But that won't be the case here.
Why? Because there is an incredible amount of heat even below the sea surface. At 575 feet below the surface, water temperatures of more than 78 degrees have been observed. So even if Melissa remains stagnant and upwells water from below, it simply will be feeding on additional warm water.
By Saturday, following an anticipated multiday stall, there are two diverging scenarios on where Melissa may go.
A northward turn would bring the storm closer to Jamaica, eastern Cuba or Haiti. Torrential tropical rains would lash Hispaniola for two or three days, leading to totals of 20 to 30 inches in the highest peaks. Disastrous flooding and mudslides would ensue, particularly in Haiti, where rampant deforestation overlapping with socioeconomic challenges yield exceptional societal vulnerability.
But this scenario would require a slightly stronger storm in the short-term. If Melissa is able to strengthen to a greater extent in the next day or two, it would sprout taller thunderstorms, which would tap into southerly winds aloft and blow the system north.
Picture a sailboat hoisting its sails. Once the sails are up, they catch the wind and sailboat is blown - the same premise applies here.
That's less likely, however, because Melissa has factors working against a shorter-term strengthening.
A westward track is perhaps more likely at this point. Melissa may be slower to organize over the next 3 or 4 days, continuing westward as it slips south of Jamaica. Then it could undergo rapid or extreme rapid intensification into a high-end hurricane by Sunday night or Monday.
While that would yield a much stronger or even top-tier hurricane, it's unclear where the storm would go by early next week.
This is the more likely scenario at this point - but uncertainties will be ironed out, and the forecast refined, in the days ahead.