The tropics are quite a mess this morning. That’s the best way to describe the scene across the Atlantic Basin. Here is a run down of what’s going on out there…
First up, Ida. This storm just keeps hanging on and taking a beating from various weather features that pass by and lash out. Steering currents remain weak but eventually Ida is expected to turn northeast and head further out in to the open Atlantic. It remains to be seen how strong it will become, some models indicate significant strengthening while others barely anything at all. It matters little really since Ida won’t be affecting any land areas.
Next we have a complex weather situation off the coast of the Southeast U.S. which has almost nothing tropical associated with it except for the fact that it’s over very warm water.
Basically we have a coastal trough of low pressure, or an elongated area of low pressure as opposed to a focused surface low, hanging around just offshore of the Carolinas and Virginia. The coastal trough alone is not a big problem but when we factor in these enormous areas of high pressure moving by to the north, then things get interesting.
Wind is created by the difference between areas of high and low pressure. I think we can all understand that concept pretty well. The greater the difference between high and low pressure, the stronger the wind. We call this a gradient, like going down a steep hill versus a gradual slope. Now imagine the wind blowing over a fairly long stretch of water, we call this a fetch. The more distance the wind blows from a certain direction over the water, the higher the waves become. This is important in understanding the situation along portions of the Southeast and Mid-Atlantic states over the next few days.
Global models indicate that the coastal trough will remain in place for the next few days with possible ripples of weak low pressure developing along the trough, moving northeast with time. This, in combination with strong Canadian high pressure in the Northeast, will help to squeeze the pressure gradient to the point where large waves will likely result and batter parts of the coastline.
We have already seen this in areas such as the NC Outer Banks where beach erosion at the times of high tide has been an ongoing issue. I think that it will only get worse as we head in to the weekend.
In addition to the rough surf and high waves, the chance for areas of heavy rain to develop is also on the table. With very warm water in the western Atlantic, there is plenty of fuel for low pressure to tap in to and dump several inches of rain across inland areas. It’s impossible to know which locations will receive the highest rain amounts but overall, it looks like a wet and unsettled weekend for portions of the Southeast and Mid-Atlantic.
Last but not least, the Gulf. The NHC has outlined an area of interest in the southern Gulf of Mexico where a broad area of low pressure is expected to develop sometime next week. Normally this would be cause for concern but this season, the incredible amount of wind shear in the atmosphere should limit any development that does take place. None of the reliable model guidance suggests anything more than a strung-out, sheared low pressure area to form. This would limit the impact from wind and surge but the chance for very heavy rain exists and we will want to monitor this region carefully as we in to early next week.
That’s it for now – I will post a video blog update later this afternoon.
M. Sudduth 1:15 PM ET Sept 23