21 September 2023

Monitoring two new disturbances as Nigel exits the scene

Activity in the Atlantic has been relatively uneventful for the middle of September, so since my previous post on Friday, Lee did of course make landfall in Nova Scotia, Margot dissipated, and Nigel became a hurricane.  Today, Nigel is heading for colder water and won't be around much longer, but there are two areas of interest to keep an eye on.  The next two names are Ophelia and Philippe.

I'll start with Nigel.  It was upgraded to a hurricane on Monday morning and tracked north through the middle of the Atlantic.  It reached Category 2 intensity for a while late Tuesday into Wednesday, but is now a Category 1 hurricane again, and expected to become an extratropical cyclone by Friday morning as it heads toward Iceland... two weeks after leaving the African coast.

The first area of interest to watch for development is a low pressure that is beginning to form along an old stalled-out cold front.  It's centered east of the Florida peninsula and has been designated as Potential Tropical Cyclone 16 by NHC on Thursday morning.  That means it still hasn't formed, but is expected to and warrants some tropical storm warnings.

It already has characteristics that are more subtropical than tropical, but either way, it would get named and NHC will issue advisories and forecast products for it.  The forecast brings it north to a landfall in North Carolina on Saturday morning as a (sub)tropical storm. Tropical storm force winds will likely arrive in eastern NC on Friday evening.  You can find the full suite of the latest forecast products at https://www.nhc.noaa.gov/graphics_at1.shtml?start#contents

Parts of North Carolina, Virginia, and Maryland could see 2-4 feet of the storm surge from this over the weekend, and the threat of flooding rain is increasing from North Carolina up into New England.

Much further east is an easterly wave that left the African coast on Tuesday.  It's located just southwest of Cabo Verde and is expected to track generally west-northwest for the next week or so, then its future path becomes harder to predict.

This is not an Invest yet, so we are limited to global models and their ensembles for guidance.  The two skillful ones we typically look at are the American (GFS) and European (ECMWF).  These two images below show the tracks from the GFS (top) and ECMWF (bottom) ensembles, ending next Friday evening. Although both of them are pretty consistent in bringing it up to hurricane intensity by Tuesday-ish, and both of them have a general tendency to turn it north by the time gets to 60°W-ish, the GFS ensemble does have more members that show a hurricane clipping the northeast Caribbean islands.  This is something we need to watch closely, because if that route starts looking more likely, it makes the northward turn less likely which has implications in the following days.

Again, the next two names are Ophelia and Philippe and it's not clear yet which of these two systems will become a tropical (or subtropical) cyclone first.

The Accumulated Cyclone Energy, ACE, is about 142% of average for the date.

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