Low off Southeast US looks to become a Tropical Storm before moving inland early Saturday. Wind, rain, and storm surge impacts expected. #PTC16 11aEDT 21Sept2023 #NCwx #VAwx

The area off the Southeast US coast has been designated as #PTC16 - Potential Tropical Cyclone Sixteen. This allows the NHC to issue cone map, Tropical Storm & Storm Surge Watch/Warnings even though a system hasn’t formed yet for advanced lead time and communication purposes. Advisories will begin at 11aEDT 21Sept2023

Don't be caught off guard!
While NHC has 40% chance of developing sub-tropical characteristics, there's still going to be a Low pressure forming along the Southeast US coast bringing impactful gusty winds, heavy rain & coastal flooding this weekend. 21Sept2023 #NCwx #VAwx

Hurricane #Nigel finally has more of a classic hurricane look to it Tuesday morning, albeit with an incredibly distinct large eye. NHC forecasting system to turn out to sea before Bermuda (currently about 650miles (1,040km) ESE of Bermuda). 19Sept2023

Now Tropical Storm Nigel.

While nothing concrete at this time, there are some slight hints in models of some Southeast US coast tropical development mischief possible for next weekend. 16Sept2023

Fairly good agreement in models for #TD15 to head Northwest in general direction of Bermuda, then turn out to sea. 16Sept2023

Tropical Storm #Margot still making loops West of The Azores in the Atlantic. Not in great shape with wind shear and dry air around it. 16Sept2023

65mph(100km/h) Post Tropical Cyclone #Lee in the Bay of Fundy just South of Saint John. 830pEDT/930pADT 16Sept2023

Another sunrise satellite view of #Lee Saturday morning.

Post-Tropical Cyclone #Lee (lost tropical characteristics but still hurricane like impacts) between Boston & Nova Scotia. About 2,400 no power MA, 17,000 Maine. 8aEDT 16Sept2023

Hurricane Sandy(2012) lessons learned: advisories/warnings continue after 'post-tropical' status.

Outer edge of Hurricane #Lee’s rain shield just East of Boston / Nantucket Friday evening. 835pEDT 15Sept2023

Tropical Depression Fifteen likely our next named Atlantic system (#TD15 was invest #97L). 11aEDT/AST 15Sept2023

Hurricane #Lee already looking extra-tropical (losing it’s Tropical Cyclone characteristics but still may be a powerful Hurricane like system) Friday morning. Clouds and storms being pulled Northward. 15Sept2023

After Hurricane #Lee we have invest #97L in the Atlantic. Fairly good model agreement on heading generally in direction of Bermuda and possibly turn out to sea thereafter. This far out in time will still watch for potential changes to that. 14Sept2023

Hurricane #Lee Thursday afternoon 14Sept

Hurricane #Lee about 245miles (395km) WSW of #Bermuda (radar: http://www.weather.bm/tools/graphics.asp

@Agatha I think we’ll get there one day. There are a few groups out there trying to come up with something like that now, with impacts broken down into their own rating systems.

(Cont)
Are forecast storm positions from NHC improving? Cone getting smaller if they are?

Yes!

That improvement rate is slowing though. Improving the science of Hurricanes will help.

7-day cone? One day! NHC is testing in house now but error at that range still too great to publish.

(Cont)
The cone size is set so that 66% of the previous 5 year errors in storm center point positions falls within that area at each forecast point.
2023 cone represents 5yr average error(in miles) of:
12hr: 30
24hr: 45
36hr: 61
48hr: 77
60hr: 93
72hr: 114
96hr: 167
120hr: 236
(Cont)