The Caribbean is on high alert for what is expected to evolve into a slow-moving hurricane that will unleash feet of rain and destructive winds on a region that has largely avoided any tropical activity so far this Atlantic hurricane season.
AccuWeather meteorologists have been tracking this area of low pressure since early October, and on Monday evening, dubbed it a tropical rainstorm to raise public awareness of the growing threat to lives and property.
As of the late morning on Tuesday, the National Hurricane Center upgraded the system to Tropical Storm Melissa and will begin issuing advisories at 11 a.m. Eastern.
"The longer Melissa tracks to the west, the greater the chance of an impact on the U.S.," AccuWeather Chief Meteorologist Bernie Rayno said.
"The chances of a direct U.S. hit from Melissa are low right now, but it is still an option, should the tropical system make it into the western Caribbean," AccuWeather Lead Hurricane Expert Alex DaSilva added.
The U.S. concern for impacts will be in the Florida Peninsula, especially the lower portion of the Peninsula and the Keys. Strong westerly winds, driven by the jet stream, should prevent the storm from tracking into Texas, Louisiana and the panhandles of Mississippi, Alabama and Florida next week.
Satellite images early Tuesday morning revealed the storm was drifting to the west-northwest and appeared to be developing a center of circulation.
"There is some wind shear (disruptive breezes) that was holding the intensity of Melissa back right now and perhaps in the future," Rayno said. "However, water temperatures in the path of Melissa in the Caribbean are in the upper 80s F." The approximate minimum temperature for tropical development is 78-80 degrees Fahrenheit.
Steering breezes will sooner or later grab onto the storm in the Caribbean and pull it northward. Areas from Hispaniola to Cuba and Jamaica are the initial population centers that would be first affected by the storm's heavy rain, strong winds and building seas.
Even though Puerto Rico may be well east of the track of the Melissa's center, a plume of tropical moisture can still bring heavy rain and the risk of flash flooding and mudslides, which are the primary concerns for the Greater Antilles farther to the west.
The islands in the northern Caribbean that will be affected the most by the storm will highly depend on when the storm begins its turn to the north.
The AccuWeather RealImpact™ Scale for Hurricanes in the Caribbean due to Melissa is a two.
This scale, developed by AccuWeather, takes into account much more than the Saffir-Simpson Hurricane Wind Scale, which only measures wind intensity. The RealImpact™ Scale considers the economic impact, the population affected and the effects of wind, storm surge, mudslides and flooding rainfall.
The islands of Hispaniola and Cuba are mountainous, which will tend to lower the intensity of Melissa, but would also wring out excess moisture in the form of torrential rain. Slow movement and terrain effects could lead to feet of rain and life-threatening to catastrophic flooding and mudslides.
There is currently an extensive area where 4-8 inches of rain may fall with an AccuWeather Local StormMax™ of 24 inches.
Melissa may spend many days in the Caribbean. If the center manages to avoid land for a time, it could become a major hurricane.
Wind gusts from Melissa are expected to reach at least the intensity of a Category 1 hurricane on the Saffir-Simpson Hurricane Wind Scale in the Caribbean. The AccuWeather Local StormMax™ gust for the storm is currently 100 mph.
Many hours and days of strong winds can take a toll on trees, poorly constructed buildings and electrical power in the region.
Cruise, fishing and beach resort interests should take note, as conditions at sea and along the coast in the Caribbean may be stormy and dangerous for days, following a relatively tranquil summer and early autumn in the region.
If Melissa survives beyond the Greater Antilles, how well it survives will determine the magnitude of the impacts in the Bahamas and perhaps South Florida. Just as in the Caribbean, the magnitude of the impacts in these more northern areas will depend on the storm's track and ability to rebound.
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As for areas farther to the north along the U.S. East Coast, there is some risk of impacts, even if the center remains at sea. In one scenario, a non-tropical storm and front, associated with a dip in the jet stream, may work together to enhance rain, wind and seas along the Eastern Seaboard during the last few days of the month.
Even if the two features fail to interact directly and the tropical storm heads out to sea, there can still be a dose of heavy rain, wind and rough seas for a time along part of the U.S. East Coast near the end of October.