WxWatcher007

I think there’s a good chance this keeps trending a little stronger. The 50kt opening bid by the NHC is a nod to those stronger global runs. Looks pretty wet here. Not sure how that’ll trend.

Homebrew delivers.

Going tropical as of that advisory.

I’ve seen this happen a few times recently with homebrew systems. Kind of surprised the NHC wasn’t higher given the cross guidance signal on the models, particularly in the last 24 hours.

I love it.

Agree. This looks like an uncommon SE homebrew in the sense that it’s forming on an old boundary and not getting shunted ENE out to sea. Atlantic ridging FTW. Might have some good gusts along the CT and LI coast with the gradient from the developing high to the north.

PTC 16 coming at 11am now. Escalated quickly lol.

PTC 16 coming at 11 now.

Special Tropical Weather Outlook...Corrected NWS National Hurricane Center Miami FL 1000 AM EDT Thu Sep 21 2023 Corrrected time in the product For the North Atlantic...Caribbean Sea and the Gulf of Mexico: Special outlook issued to raise probabilities and update discussion Active Systems: The National Hurricane Center is issuing advisories on Hurricane Nigel, located over the central subtropical Atlantic. Off the Southeastern United States Coast (AL99): Updated...A trough of low pressure located several hundred miles east of the Florida peninsula continues to produce a large area of disorganized showers and thunderstorms. A non-tropical low pressure system is expected to form within this area by early Friday, and there are increasing chances that this system could acquire some tropical or subtropical characteristics on Friday or early Saturday while it moves generally northward toward the coast of North Carolina. Regardless of tropical or subtropical development, this low is likely to bring tropical storm force winds, heavy rain, coastal flooding, and high surf to portions of the southeast and mid-Atlantic United States coastline on Friday and into the weekend. Tropical Storm watches or warnings could be required for this system as soon as later this morning. Additional information on this system, including storm and gale warnings, can be found in High Seas Forecasts and products from your local National Weather Service office. * Formation chance through 48 hours...medium...50 percent. * Formation chance through 7 days...medium...50 percent.

Wondered why they didn’t go higher earlier. Special Tropical Weather Outlook...Corrected NWS National Hurricane Center Miami FL 1000 AM EDT Thu Sep 21 2023 Corrrected time in the product For the North Atlantic...Caribbean Sea and the Gulf of Mexico: Special outlook issued to raise probabilities and update discussion Active Systems: The National Hurricane Center is issuing advisories on Hurricane Nigel, located over the central subtropical Atlantic. Off the Southeastern United States Coast (AL99): Updated...A trough of low pressure located several hundred miles east of the Florida peninsula continues to produce a large area of disorganized showers and thunderstorms. A non-tropical low pressure system is expected to form within this area by early Friday, and there are increasing chances that this system could acquire some tropical or subtropical characteristics on Friday or early Saturday while it moves generally northward toward the coast of North Carolina. Regardless of tropical or subtropical development, this low is likely to bring tropical storm force winds, heavy rain, coastal flooding, and high surf to portions of the southeast and mid-Atlantic United States coastline on Friday and into the weekend. Tropical Storm watches or warnings could be required for this system as soon as later this morning. Additional information on this system, including storm and gale warnings, can be found in High Seas Forecasts and products from your local National Weather Service office. * Formation chance through 48 hours...medium...50 percent. * Formation chance through 7 days...medium...50 percent.

It does, but the general trend has been stronger on the globals.

It’s homebrew/hybrid or nothing at all. MDR season is done as far as NE is concerned.

Now designated as Invest 99L.

Now designated as Invest 99L.

Look at SHIPS. This one looks legit on the guidance. GFS leads the way. We've had some good quick spin ups in recent years off the SE coast.

For those that care, I think this has a really good shot of becoming a named subtropical storm (Ophelia) and a decent shot of acquiring tropical characteristics right before a NC landfall. The guidance has continued to trend stronger and more organized with the low as it makes that final approach. GFS has led the way on this one, but if anything the Euro has become the wetter model here south of pike. 06z Euro wettest yet of those euro runs.

Forgot to add the other two images. SSTs are obviously warm and there is OHC near the coast that would support subtropical development and tropical designation near the coast if this system had enough time. In the whole scheme of things, the subtropical/tropical designation doesn't matter, but a tropical designation could mean a more organized rain shield and wind field into the coastal areas.

I've been on the Euro is not infallible train for years lol. Not what it used to be. Thread done

After the incredible pace of tropical activity in the MDR, we're reaching the homebrew portion of the 2023 Atlantic hurricane season. On cue, we have a potential system off the southeast coast that is being tracked by the NHC. 1. Western Atlantic: A trough of low pressure located several hundred miles east of the Florida peninsula is producing a large area of disorganized showers and thunderstorms. A non-tropical low pressure system is expected to form within this area by early Friday, and this system could acquire some subtropical characteristics on Friday or early Saturday while it moves generally northward toward the coast of North Carolina. Regardless of subtropical development, this low is likely to bring gusty winds to gale force, heavy rain, and high surf to portions of the Southeast and Mid-Atlantic United States on Friday and into the weekend. Additional information on this system, including storm and gale warnings, can be found in High Seas Forecasts and products from your local National Weather Service office. * Formation chance through 48 hours...low...30 percent. * Formation chance through 7 days...medium...40 percent. The guidance, which was split even yesterday on impacts and development of this low, looks to have coalesced into a forecast for an impactful event in North Carolina into the Mid-Atlantic, with reduced impacts possible even further up the coast. Particularly interesting is that the guidance has trended stronger with the potential low, increasing the odds that this becomes a subtropical storm, and introducing the possibility that it attains tropical characteristics before a landfall on Saturday. Let's take a closer look at the overall setup and potential in the region. First, this is a standard way to get subtropical or tropical genesis off the SE coast. A stalled frontal boundary is serving as a focal point for convective activity, which will allow for the formation of a non-tropical (baroclinic) low. Yesterday was when we first started seeing the strong convective bursting needed for the development of an eventual sub/tropical low, and it has continued into today as expected. Looking at the visible images so far today, you can see the robust convection off the SE coast, but there's still work to do in terms of organizing. To recap, for a tropical system, which is unlikely early on, you need to see persistent convection around a closed low that only acquires its energy from the ocean. For a subtropical system, convection can be removed from the center, but the system needs to essentially be a hybrid that acquires its energy from both the ocean and baroclinic (think nor'easter temperature contrast) sources. With guidance trending stronger, I think this one has a very good shot of becoming our next named storm, Ophelia. Frequently, we see these boundary systems develop and slide harmlessly OTS on a NE heading, but in this case, as the system develops, it will drift north/NNW around an Atlantic ridge. It's increasingly clear that the center of the system will landfall over eastern NC and then drift into the Mid-Atlantic, before getting shunted ENE and back offshore further north. Watch the Atlantic ridge build in first, drawing the system into the MA. Then another big ridge blocks it from continuing north and the low (or remnants) are driven eastward back offshore and eventually OTS off the New England coast. This track, and gradient between the low and high pressure to the north means rain and a lot of it, along with strong winds at the shoreline. Tropical storm force winds look likely at the shoreline, even far away from the low center. Rather than a smaller gif, I want to focus on two images from the GFS below. This is fascinating. The first, valid early tomorrow morning, has a 1008mb low that has developed. The exact pressure doesn't matter here really, just look at the depiction and trend with the second image. Friday morning this is a lopsided, but intensifying low. This is when it would be nearing subtropical designation. However, note what it looks like 24 hours later, early Saturday morning. This has shown up on a variety of models--the consolidation of the wind field right before landfall in NC. Look at the pressure drop as well which amounts to 15mb in 24 hours. It drops a little more in the next six hours as well. That tells me that as this approaches the coast and crosses the Gulf Stream, it may acquire enough tropical characteristics to be designated as tropical. This is a strong low depicted by the guidance, which enhances rainfall potential IMO as well. That will be something to watch closely, as we've seen a history of these SE lows spinning up quickly on final approach. The Bay and coastal areas should see water rise and strong winds that will make this impactful. With parts of the inland region in moderate to severe drought, any rain would be beneficial. It's still unclear how far inland the heavy rain gets, but this is the best chance this summer of significant rain further west. Which isn't saying much unfortunately. We'll see how the trends evolve, but a heavy rain event is looking increasingly likely across part of the region.

Is there any objection to me starting a thread for this event?

Yeah you could tell yesterday that the trend was upward. Once a low develops, it starts to intensify fairly quickly for how little time it has over water. I still think subtropical, but honesty if those model depictions verify it looks like it could become tropical right before landfall. 8am 1. Western Atlantic: A trough of low pressure located several hundred miles east of the Florida peninsula is producing a large area of disorganized showers and thunderstorms. A non-tropical low pressure system is expected to form within this area by early Friday, and this system could acquire some subtropical characteristics on Friday or early Saturday while it moves generally northward toward the coast of North Carolina. Regardless of subtropical development, this low is likely to bring gusty winds to gale force, heavy rain, and high surf to portions of the Southeast and Mid-Atlantic United States on Friday and into the weekend. Additional information on this system, including storm and gale warnings, can be found in High Seas Forecasts and products from your local National Weather Service office. * Formation chance through 48 hours...low...30 percent. * Formation chance through 7 days...medium...40 percent.

It has…struggled…

I disagree in part. Nino definitely lost during the last four weeks, but the MDR is more hostile than it was even a week ago, particularly with SAL. Not enough to keep that wave from developing, but it may stunt its development for a bit. I do think we’re transitioning to the western Caribbean and SE coast as we approach October but that’s not saying much because that’s climo. Will waves keep rolling off, yeah, but development is probably going to be more delayed or halted altogether, especially if shear picks up in the eastern Caribbean.

Canadian was pretty high impact. GFS as you said kind of slid everything south but it’s close. There’s still a lot of spread on this low’s intensity and progression for what’s essentially a short range forecast. It’s hard to lean against persistence—what rain event have we missed since July—but that high may keep us dry.