• Bryan Norcross

Developing disturbance to bring strong winds, coastal flooding, and heavy rain to parts of the South

Disturbance #1 is an elongated area of lower pressure stretching across the Caribbean from the Dominican Republic to Venezuela. This system, combined a strong dip in the jet stream, is already causing heavy rain over Puerto Rico and the surrounding islands. Flood Watches are in effect there due to forecasts of persistent rain over the next few days.


The dip in the jet stream is forecast to break off into a large upper-level disturbance that will meander in the vicinity of the Bahamas over the next several days. This system combined with the nascent low pressure over the Caribbean are expected to create a non-tropical low-pressure system in the vicinity of Puerto Rico in a day or two.


This evolutionary process is the same one that creates nor'easters farther north, but it's happening in the tropics.



As we've already seen a few times this year, when non-tropical low-pressure systems track over warm tropical ocean water, they can evolve into systems with tropical characteristics – a subtropical depression or storm if non-tropical aspects remain, and a tropical depression or storm if they don't.


The upper-level disturbance will create a donut of steering winds which should pull the low-pressure system out of the Caribbean and then arc it in the direction of Florida.


The most impactful component of this event appears less likely to be related to the evolving disturbance itself, although we'll keep an eye on that. But this whole combo system will create a broad general area of low pressure over the Bahamas. A strong high-pressure system moving off the New England coast is going to try to fill in that low pressure. The result is likely to be strong winds along the Southeast coast and perhaps part of the Mid-Atlantic coast as well.


Winds gusting over 40 mph will push ocean water toward the coast and into bays and harbors just as the full moon is creating extra-high tides. Significant coastal flooding is possible toward the middle of next week.


Exactly where the strongest push of air off the ocean will occur remains to the seen, but it will probably be over a very large area hundreds of miles from wherever the disturbance develops and tracks.


Everybody from the Mid-Atlantic south to Florida, and especially in the Carolinas, should be aware of potential bad weather and coastal flooding next Tuesday and Wednesday, plus or minus. The timing and details are subject to change.


It appears the disturbance will get involved with a coming cold front later next week and be absorbed.


On the uncertainty scale, the coastal effects over a large part of the central and southern East Coast appear likely due to the influence of the strong high-pressure system to the north. The exact evolution of the disturbance itself, and whether it is of much consequence as a storm system in the Bahamas or Florida is an open question.



Farther north, Disturbance #2 is another non-tropical low-pressure system over the ocean east of Bermuda. Over the weekend, it might acquire some tropical characteristics and add to the hurricane season's statistics. In any case, it won't be a threat to land.


In the southern Gulf of Mexico, Tropical Depression Lisa is on its last legs. It will become a remnant area of low pressure soon and not be of further consequence.


Nothing else is imminent, but the autumn ocean is always full of non-tropical low-pressure systems. As long as the water is warm, and in many cases unusually warm, systems will have to be watched.