It looks like the United States and Gulf of Mexico are safe from whatever may develop from this disturbance, but the risk is increasing for places like Nicaragua, Honduras and Belize.
After a quiet start to hurricane season, a spurt of activity has brought this year’s activity closer in line with the average. Fiona and Ian contributed the most to making up the deficit in storminess, and the Atlantic basin is now only 20 percent behind the mean in terms of ACE, or Accumulated Cyclone Energy. That is a measure of how much energy storms harvest from warm ocean waters and expend on strong winds.
In addition to the fledgling storm near the Lesser Antilles, there is also a tropical depression a little under 500 miles west of the Cabo Verde Islands, but it is not expected to strengthen or receive a name.
Potential Caribbean system developing
As of midmorning Wednesday, the system over the Windward Islands was bringing heavy rain there and across northern Venezuela. Trinidad and Tobago were being soaked as well, with robust shower and thunderstorm activity blossoming from the tropical wave.
There were a few limiting factors to the storm. It lacks a “closed circulation.” That means winds are rotating, but they don’t make a complete circle.
That can be seen on scatterometer data — or measurements from a satellite-based instrument that ascertains wind speed and direction through the motion of clouds and ocean waves. We can see there does exist obvious curvature, but there is not a westward “wraparound” of wind. Until that happens, the system will not be declared a tropical depression.
Instead, what’s visible is an axis of vorticity, or spin. If a lobe of that spin along the wind shift line east of Trinidad and Tobago gets vertically stretched by a thunderstorm, it could become the de facto center. Then the storm would organize itself around that column of rotation, and likely become a tropical storm.
For the time being, the system is working against strong wind shear, or a disruptive change of wind and/or direction with height, to its north. That is conspiring to knock the storm off-kilter and hamper its organization. Wind shear is lesser to the south, which is why the storm may be hewing south and scraping along the South American coastline.
In the days ahead, it will probably escape that shear as it approaches the ABC Islands (Aruba, Bonaire and Curaçao) while gradually consolidating.
The National Hurricane Center pegs the disturbance as having an 80 percent chance of eventual development. Weather models indicate the system will probably become a tropical storm by the end of the week as it outruns shear.
Despite the recent passage of Ian, sea surface temperatures in the Caribbean are still very warm, and will be conducive to intensification. What’s different this time, however, is that the upper air pattern won’t be quite as conducive to rapid intensification.
With Ian, a clockwise-spinning high pressure system at the upper levels was present aloft to aid in the storm’s “outflow,” or exhaust; the more air that exits a storm from above, the more warm, humid air that can enter to fuel the storm. This time around, high pressure looks to be displaced to the north-northwest.
Still, the new system may eventually attempt to become a hurricane, with Julia being the next name on the list. Whatever it becomes should reach Nicaragua by Sunday into Monday. Rainfall totals of 12 to 24 inches are possible, especially in the higher terrain, where mudslides and flooding can be expected.
High pressure at the mid levels should keep the system shunted far enough south that it cannot turn north toward the Gulf of Mexico or Lower 48.