September 2019 - Warm End of September

[DoctorMu]

I hope the models converge soon.

They already did overnight, then quickly lost that consensus. That happens sometimes...especially when the steering currents collapse.

Yep. Dorian could have a forward speed around 4 mph for 2 days!
All the models converged on W Palm Beach yesterday. HRRR is splitting the difference.

[DoctorMu]

18Z GFS takes Dorian right along the coast with multiple landfalls.

Almost the same for CMC.

[DoctorMu]

Waaaaaaayyyyy too early to make any assumptions re: Dorian path. Small error leads to large differential consequences.



Hope for the best; expect the worst.

[srainhoutx]

Dorian now a Category 4 Hurricane.

[Andrew]

Interesting with the intensification occurring today Dorian is feeling the impacts of a weak upper-level ridge pushing it more west than Northwest/WNW. Could result in some interesting model runs if this West/WNW movement continues for a little bit longer especially with how close models already are with landfall.

[DoctorMu]

Dorian now a Category 4 Hurricane.

A fly in the ointment is that storms this powerful can impact steering conditions as high pressure overhead builds.

Incredibly dangerous as Dorian approaches even warmer water.

[MontgomeryCoWx]

Don’t jack up my Clemson/Charleston trip Dorian... you bastard!

[Cpv17]

Don’t jack up my Clemson/Charleston trip Dorian... you bastard!

Your Aggies will have to play leaps and bounds better just to stay in the game with Clemson. They looked horrible against a cupcake Texas State team. But it looks like your trip might be okay. Hoping for Dorian to go ots.

[srainhoutx]

The National Hurricane Center is monitoring a broad area of low pressure in the SE Gulf that is showing some signs of development as it nears the Western Gulf Labor Day and early next week. That SE Gulf broad low could bring heavy rain near the Coast and lower chances inland on Labor Day and next Tuesday. A word of caution regarding Major Hurricane Dorian and the models. A G-IV High Altitude recon mission did not fly yesterday afternoon and therefore no new data for the 00Z suite of guidance. There are missions schedule to fly today and beyond. The strength of the Bermuda Ridge has not been accurately sampled and those thinking that Florida is in the clear need to continue vigilance and prepare for a Major Hurricane Impact along the East Coast of Florida, Georgia, South Carolina and Eastern North Carolina.

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Sat Aug 31 2019

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Hurricane
Dorian, located a few hundred miles east of the northwestern
Bahamas.

1. A tropical wave located about midway between the coast of Africa
and the Cabo Verde Islands continues to produce a large area of
showers and a few thunderstorms. Environmental conditions appear
conducive for development of this system, and a tropical depression
could form next week while the system moves across the eastern
tropical Atlantic Ocean. Heavy rainfall is possible over portions
of the southern Cabo Verde Islands during the next few days, and
interests on those islands should monitor the progress of this
system.
* Formation chance through 48 hours...low...20 percent.
* Formation chance through 5 days...medium...60 percent.

2. A broad area of low pressure located over the southeastern Gulf of
Mexico is producing disorganized showers and thunderstorms. Some
gradual development of this system is possible during the next
several days while it moves slowly westward across the southern and
southwestern Gulf of Mexico.
* Formation chance through 48 hours...low...10 percent.
* Formation chance through 5 days...low...20 percent.

Forecaster Zelinsky

[srainhoutx]

Saturday morning Gulf Of Mexico tropical disturbance Update from Jeff:

A weak surface low has developed over the extreme SE Gulf of Mexico over the last 24 hours and is moving slowly westward. This is the same system that global forecast models have been showing attempting to develop into a weak tropical system in the Gulf of Mexico this weekend into next week. A review of overnight model guidance continues to hint at the potential for a weak system to develop and track generally westward or west-southwest across the south-central and then southwestern Gulf this week approaching the eastern Mexican coast late next week. This track is due to building high pressure over TX starting on Monday and Tuesday.

NHC gives the system a 20% chance of formation over the next 5 days. At this time any impacts along the TX coast would be an increase in moisture starting early next week and potentially increasing seas by mid week, but at the moment any direct impacts appear to stay south of the upper TX coast.

[srainhoutx]

Saturday morning Major Hurricane Dorian Update from Jeff:

Hurricane warnings are in effect for the northern Bahamas

Dorian becomes a powerful category 4 hurricane with 145mph sustained winds.

A rightward guidance trend yesterday and overnight suggests an increasing threat for impacts in GA, SC, and NC

Discussion:
Dorian is a well developed powerful hurricane with a clearly defined 12-15nm wide eye embedded within a ring of deep convective storms. The western side of the system may be ingesting some dry air and there may be a hint at weak shear as the western eyewall is more narrow in that area compared to the eastern side of the storm. The last USAF mission recorded significant pressure falls yesterday from 970mb in the morning to 946mb in the evening indicating rapid intensification with maximum sustained wind speeds increasing from 110mph yesterday morning to 145mph this morning. A new plane will be within Dorian shortly, but based on the satellite images this morning it appears Dorian is likely about the same intensity as when the last plane departed.

Track:
There has been some adjustment of the global track guidance and official NHC forecast to the right (east) overnight. Dorian has turned toward the WNW and this motion with a turn toward the west will continue for the next 24-36 hours bringing the core of Dorian into the northern Bahama Islands. The forward speed will slow and it is possible that Dorian stalls over the northern Bahamas, this is in response to the sub-tropical ridge north of the hurricane weakening and breaking down on its westward flank as a short wave trough moves across the Great Lakes into the NE US. This trough may be strong enough to grab Dorian and turn the hurricane NNW/N offshore the east FL coast and then a turn to the NNE off the SE US coast. Very small scale changes in the steering flow with Dorian by Monday and Tuesday could result in a landfall over eastern FL or the system remaining offshore. Direct impacts from Dorian are now possible into GA, SC, and NC based on the latest trends, but the eastern coast of FL is still within the error cone of the NHC track and many of the global model ensemble tracks still show direct impacts to the FL east coast. Given the collapse of defined steering currents over the northern Bahamas, uncertainty as to when Dorian turns toward the north is high.

Intensity:
Dorian is a powerful hurricane in an environment favorable for continued intensification. Powerful hurricanes in such environments tend to see intensity changes reflective of eyewall replacement cycles with a decrease in intensity as a new outer eyewall forms and then an increase in intensity as that outer eyewall contracts inward and the old inner eyewall dissolves. The most important factors of an eyewall replacement cycle is that the wind field tends to expand outward during such periods. Dorian is expected to impact the northern Bahamas as a powerful category 4 hurricane. As Dorian begins to turn NNW/N near the FL coast the interaction of the circulation with land and some increasing vertical wind shear will likely help weaken the system as it moves toward the SE US coast. Should Dorian make landfall in FL, the intensity forecast for the longer ranges is too high and would need to be reduced.

[srainhoutx]

Category 4 Major Hurricane Dorian this morning. Dorian is a small powerful Hurricane. Do not let that small size mislead you. Whoever experiences the inner core of Dorian will face almost certain destruction. I am really worried for the Northern areas of the Bahamas this morning.

[MontgomeryCoWx]

That is a tightly wrapped bowling ball

[srainhoutx]

We wish Josh a SAFE and successful intercept...

Josh Morgerman‏Verified account @iCyclone · 18m18 minutes ago
Goin' for it. Last flight into Abaco Islands #Bahamas before it shuts down. I passionately hate Island Roulette. But I hate standing on my hind legs for three days to lick the bland edges of an unraveling recurver even more. I may go down in flames on this chase. Oh well. #DORIAN

[Cpv17]

Florida is almost in the clear of this thing now. Crazy how much models have changed in the past 24-48 hours.

[Andrew]

While I don't think Florida is clear of this storm yet, for those who are interested I created a trend gif (click on the image below so it plays) of the GFS to show why models are trending east over the last day. Keep an eye on the trough over Quebec into the Northeast United States, because models have trended stronger and deeper making all the difference. In the previous couple of days, models have actually indicated a weak (relatively flat) ridge would setup over the SE United States this weekend behind the trough but that is no longer the case anymore. The trough is now much deeper and breaking down any attempt for a blocking pattern. This is why the speed of Dorian has increased slightly, but more importantly, it does not track as far west. This will be something we need to monitor going tomorrow and Monday to see if models continue this trend or start to walk back west some. It also shows the importance of increased sounding data and resolution and how much influence it can have.

[Cpv17]

While I don't think Florida is clear of this storm yet, for those who are interested I created a trend gif (click on the image below so it plays) of the GFS to show why models are trending east over the last day. Keep an eye on the trough over Quebec into the Northeast United States, because models have trended stronger and deeper making all the difference. In the previous couple of days, models have actually indicated a weak (relatively flat) ridge would setup over the SE United States this weekend behind the trough but that is no longer the case anymore. The trough is now much deeper and breaking down any attempt for a blocking pattern. This is why the speed of Dorian has increased slightly, but more importantly, it does not track as far west. This will be something we need to monitor going tomorrow and Monday to see if models continue this trend or start to walk back west some. It also shows the importance of increased sounding data and resolution and how much influence it can have.

What’s your gut telling you Andrew?

[Andrew]

While I don't think Florida is clear of this storm yet, for those who are interested I created a trend gif (click on the image below so it plays) of the GFS to show why models are trending east over the last day. Keep an eye on the trough over Quebec into the Northeast United States, because models have trended stronger and deeper making all the difference. In the previous couple of days, models have actually indicated a weak (relatively flat) ridge would setup over the SE United States this weekend behind the trough but that is no longer the case anymore. The trough is now much deeper and breaking down any attempt for a blocking pattern. This is why the speed of Dorian has increased slightly, but more importantly, it does not track as far west. This will be something we need to monitor going tomorrow and Monday to see if models continue this trend or start to walk back west some. It also shows the importance of increased sounding data and resolution and how much influence it can have.

What’s your gut telling you Andrew?

I think the Carolinas are more under the gun now but models continue to even shift away from the coast which is very good news. I know if this does miss land overall a lot of people are going to be upset about all the preparations being made for a miss but it goes to show why it is so important for upper air missions and increased sounding frequencies. With all that said, no one in the cone should let their guard down because we are still 3-5 days out from a potential landfall depending where you live. Overall, I like the trend and hope it continues.

[Cromagnum]

When I see other Mets on S2K posting upper level winds like this I don't see why the sharp turn north is in the cards. Seems like it would shoot the gap.

[srainhoutx]

48 hours without G-IV data likely impacted the ability to fully understand the upper air dynamics for Dorian. The G-IV is sampling now after some sort of incident that apparently did damage to the windshields of that aircraft.