Tropical Storm Danny May Become First Hurricane of 2015 on Path Toward Caribbean
By Alex Sosnowski, AccuWeather.com Senior Meteorologist
August 20, 2015; 6:41 AM ET
The system became a tropical depression on Tuesday morning and could become a hurricane on or before Friday as it continues to move through generally favorable atmospheric conditions in the short term.
The system moved westward across Africa during the first part of August and was moving westward this week over the south-central Atlantic Ocean at 10-15 mph (15-25 kph).
Satellite imagery of Tropical Storm Danny (Image/NOAA)
When a closed circulation near the sea surface has been confirmed, a tropical depression is born. When sustained winds around the circulation reach 39 mph (63 kph), a tropical depression is upgraded to a tropical storm. For a system to become a hurricane, sustained winds must reach 74 mph (119 kph).
Danny is currently about 1,200 miles east of Windward and Leeward islands just north of the equator.
Danny follows Ana, Bill and Claudette from earlier this season. None of the first three storms reached hurricane status. So, if Danny becomes a hurricane, then it would be the first of the 2015 Atlantic season.
Much of the islands in the Caribbean Sea are in drought and would trade the inconvenience and hazards that a modest tropical storm would bring for rainfall. Even a poorly organized tropical depression or storm could bring an uptick in drenching showers and thunderstorms, provided the system tracks close by.
The exact track of the system beyond several days is questionable at this point.
A general track to the west-northwest is most likely through this weekend, with Danny being guided along by the oval-shaped circulation of high pressure over the central Atlantic.
On that track and present speed, Danny is expected to cross the Windward or Leeward islands during Monday. Soon thereafter, Danny will enter the Caribbean.
A curve to the northwest and fluctuation in strength are also possibilities with Danny.
Should the system ramp up quickly to a hurricane, then a jog to the northwest would be a greater possibility.
Danny has some atmospheric parameters working for it and against it at this point.
Dry air just north of the storm will occasionally wrap in and result in fluctuation in strength and organization through the weekend. Too much dry air could wrap in and choke off the storm's moisture supply.
Waters along Danny's projected path are sufficiently warm to support further strengthening.
The tropical storm is currently passing through a zone where winds aloft are light, which favors development.
Strong winds aloft (wind shear) can prevent a tropical system from developing or cause an organized tropical system to weaken.
The winds aloft over Danny's path may strengthen next week.
According to AccuWeather Meteorologist Evan Duffey, wind shear has been strong over the Caribbean Sea during much of hurricane season thus far.
"The most likely time for Danny to strengthen is prior to crossing into the Caribbean, since beyond this point wind shear may be too hostile," Duffey said.
There are two other areas of concern in the Atlantic.
A significant area of disturbed weather is forecast to soon emerge off Africa later this week.
"Steering winds favor a more northwest track with this second system when compared to the existing tropical depression and potential impacts to land will likely be reduced, should it develop this weekend into next week," Duffey said.
A track into the central Atlantic, well away from land areas is most likely with the second system.
During El Nino, the number of named tropical systems in the Atlantic basin tends to be lower than average.
AccuWeather is forecasting eight tropical storms, four hurricanes and one major hurricane for the 2015 season with two to three landfalls in the United States. Ana and Bill made landfall in the U.S. during May and June respectively