MIAMI – The broad area of low pressure well south of the Florida Keys came from an old cold front and an upper-air disturbance. It’s pulling moisture out of the tropics and slinging it into South Florida, propelled by the strong winds coming in from the ocean. A strong high-pressure area to the north is providing those winds and blocking the messy low from going anywhere fast.
But that’s all going to change later today. The high-pressure system will head east at the same time a stronger upper-air disturbance arrives from the Gulf to scoop up the messy low and push it toward the northern Bahamas. That new disturbance will start the process of energizing the low and beginning the organizing process.
The new upper disturbance is related to the system that caused torrential rain and violent weather across east Texas and Louisiana the last couple of days.
As the high-pressure system moves away, the winds should let up today across South Florida, even as the slowly organizing low-pressure system moves by just offshore. By tonight, the low should be pulling dry air over the state from the north as the center of the system tracks over the Bahamas, bringing in better weather.
There is a lot of concern on Abaco and Grand Bahama since people are living in mobile homes or homes covered in tarps and tents – the legacy of Hurricane Dorian. Everybody there should prepare the best they can for some periods of heavy rain and gusty winds, but the indications are that the winds won’t get much worse than they already have been, except perhaps in gusts.
The fact that the center of the developing system is forecast to track over or near the northern Bahamas does not mean that the worst weather will come there. As long as the system stays relatively disorganized – and it’s expected to only slowly organize during its trek over the Bahamas – the center is irrelevant to the weather. In disorganized systems, the worst weather is often on the periphery of the circulation.
Unlike in a hurricane where eyewall around the circulation center has the strongest winds and greatest effect, the gusty winds and heaviest rain in a disorganized system are more scattershot in the circulation. The main point is, don’t focus on the exact track of the system, as it won’t tell you where most of the cells or bands with the heaviest rain or the gustiest winds are going to be.
As the system is moving through or near the Bahamas, the atmospheric conditions are expected to become conducive for organization so that a decently organized circulation emerges into the open ocean off North Florida and the Southeast coast.
Since the system originated from non-tropical entities – the old front and the upper-level disturbances – it will likely start out as a hybrid system. We call those subtropical. Eventually, the remnants of those non-tropical components may wash out, but that’s uncertain. If winds in the circulation reach 40 mph while those legacy parts still exist, the system will be called Subtropical Storm Arthur.
Whatever happens, it says nothing about the hurricane season to come. In years when cold fronts come far south late in the spring, this is the kind of system that can emerge. When we get into the tropical season, we look to the Atlantic for storms to strengthen due to the warm ocean water.
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